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Piot, M. y R. von Glasow. "The chemistry influencing ODEs in the Polar Boundary Layer in spring: a model study". Atmospheric Chemistry and Physics Discussions 8, n.º 2 (16 de abril de 2008): 7391–453. http://dx.doi.org/10.5194/acpd-8-7391-2008.
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Abstract. Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic cycles involving reactive halogens are now recognized to be of main importance for Ozone Depletion Events (ODEs) in the Polar Boundary Layer (PBL). We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2, BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H4, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induced a shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. Cases with elevated mixing ratios of HONO, NO2, and RONO2 induced a shift to BrNO2/BrONO2. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). These shifts to HOBr/HBr also hindered the BrO self-reaction. In these cases, the ozone depletion was slowed down, where increases in H2O2 and HONO had the greatest effect. The tests with increased mixing ratios of C2H4 highlighted the decrease in HOx which reduced the production of HOBr from bromine radicals. In addition, the direct reaction of C2H4 with bromine atoms led to less available reactive bromine. The aerosol debromination was therefore strongly reduced. Ozone levels were highly affected by the chemistry of C2H4. Cl2-induced ozone depletions were found unrealistic compared to field measurements due to the rapid production of CH3O2, HOx, and ROOH which rapidly convert reactive chlorine to HCl in a "chlorine counter-cycle". This counter-cycle efficiently reduces the concentration of reactive halogens in the boundary layer. Depending on the relative bromine and chlorine mixing ratios, the production of CH3O2, HOx, and ROOH from the counter-cycle can significantly affect the bromine chemistry. Therefore, the presence of both bromine and chlorine in the air may unexpectedly lead to a slow down in ozone destruction. For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosols (Cl2 or BrCl) increased.
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Gil, Junsu, Meehye Lee, Jeonghwan Kim, Gangwoong Lee, Joonyoung Ahn y Cheol-Hee Kim. "Simulation model of Reactive Nitrogen Species in an Urban Atmosphere using a Deep Neural Network: RNDv1.0". Geoscientific Model Development 16, n.º 17 (13 de septiembre de 2023): 5251–63. http://dx.doi.org/10.5194/gmd-16-5251-2023.
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Abstract. Nitrous acid (HONO) plays an important role in the formation of ozone and fine aerosols in the urban atmosphere. In this study, a new simulation approach is presented to calculate the HONO mixing ratios using a deep neural technique based on measured variables. The Reactive Nitrogen Species using a Deep Neural Network (RND) simulation is implemented in Python. The first version of RND (RNDv1.0) is trained, validated, and tested with HONO measurement data obtained in Seoul, South Korea, from 2016 to 2021. RNDv1.0 is constructed using k-fold cross validation and evaluated with index of agreement, correlation coefficient, root mean squared error, and mean absolute error. The results show that RNDv1.0 adequately represents the main characteristics of the measured HONO, and it is thus proposed as a supplementary model for calculating the HONO mixing ratio in a polluted urban environment.
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Vakhrusheva, Tatyana V., Daria V. Grigorieva, Irina V. Gorudko, Alexey V. Sokolov, Valeria A. Kostevich, Vassili N. Lazarev, Vadim B. Vasilyev, Sergey N. Cherenkevich y Oleg M. Panasenko. "Enzymatic and bactericidal activity of myeloperoxidase in conditions of halogenative stress". Biochemistry and Cell Biology 96, n.º 5 (octubre de 2018): 580–91. http://dx.doi.org/10.1139/bcb-2017-0292.
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Myeloperoxidase (MPO), found mainly in neutrophils, is released in inflammation. MPO produces reactive halogen species (RHS), which are bactericidal agents. However, RHS overproduction, i.e., halogenative stress, can also damage host biomolecules, and MPO itself may be targeted by RHS. Therefore, we examined the susceptibility of MPO to inactivation by its primary products (HOCl, HOBr, HOSCN) and secondary products such as taurine monochloramine (TauCl) and taurine monobromamine (TauBr). MPO was dose-dependently inhibited up to complete inactivity by treatment with HOCl or HOBr. TauBr diminished the activity but did not eliminate it. TauCl had no effect. MPO became inactivated when producing HOCl or HOBr but not HOSCN. Taurine protected MPO against inactivation when MPO was catalyzing oxidation of Cl− to HOCl, whereas taurine failed to prevent inactivation when MPO was working with Br−, either alone or in combination with Cl−. SCN− interfered with HOCl-mediated MPO inhibition. UV–vis spectra showed that heme degradation is involved in HOCl- and HOBr-mediated MPO inactivation. A negative linear correlation between the remaining chlorinating activity of HOCl- or HOBr-modified MPO and Escherichia coli survival upon incubation with MPO/H2O2/Cl− was found. This study elucidated the possibility of MPO downregulation by MPO-derived RHS, which could counteract halogenative stress.
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Fang, Yuyu y Wim Dehaen. "Fluorescent Probes for Selective Recognition of Hypobromous Acid: Achievements and Future Perspectives". Molecules 26, n.º 2 (12 de enero de 2021): 363. http://dx.doi.org/10.3390/molecules26020363.
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Reactive oxygen species (ROS) have been implicated in numerous pathological processes and their homeostasis facilitates the dynamic balance of intracellular redox states. Among ROS, hypobromous acid (HOBr) has a high similarity to hypochlorous acid (HOCl) in both chemical and physical properties, whereas it has received relatively little attention. Meanwhile, selective recognition of endogenous HOBr suffers great challenges due to the fact that the concentration of this molecule is much lower than that of HOCl. Fluorescence-based detection systems have emerged as very important tools to monitor biomolecules in living cells and organisms owing to distinct advantages, particularly the temporal and spatial sampling for in vivo imaging applications. To date, the development of HOBr-specific fluorescent probes is still proceeding quite slowly, and the research related to this area has not been systematically summarized. In this review, we are the first to review the progress made so far in fluorescent probes for selective recognition and detection of HOBr. The molecular structures, sensing mechanisms, and their successful applications of these probes as bioimaging agents are discussed here in detail. Importantly, we hope this review will call for more attention to this rising field, and that this could stimulate new future achievements.
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Chai, Jiajue, David J. Miller, Eric Scheuer, Jack Dibb, Vanessa Selimovic, Robert Yokelson, Kyle J. Zarzana et al. "Isotopic characterization of nitrogen oxides (NO<sub><i>x</i></sub>), nitrous acid (HONO), and nitrate (<i>p</i>NO<sub>3</sub><sup>−</sup>) from laboratory biomass burning during FIREX". Atmospheric Measurement Techniques 12, n.º 12 (29 de noviembre de 2019): 6303–17. http://dx.doi.org/10.5194/amt-12-6303-2019.
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Abstract. New techniques have recently been developed and applied to capture reactive nitrogen species, including nitrogen oxides (NOx=NO+NO2), nitrous acid (HONO), nitric acid (HNO3), and particulate nitrate (pNO3-), for accurate measurement of their isotopic composition. Here, we report – for the first time – the isotopic composition of HONO from biomass burning (BB) emissions collected during the Fire Influence on Regional to Global Environments Experiment (FIREX, later evolved into FIREX-AQ) at the Missoula Fire Science Laboratory in the fall of 2016. We used our newly developed annular denuder system (ADS), which was verified to completely capture HONO associated with BB in comparison with four other high-time-resolution concentration measurement techniques, including mist chamber–ion chromatography (MC–IC), open-path Fourier transform infrared spectroscopy (OP-FTIR), cavity-enhanced spectroscopy (CES), and proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF). In 20 “stack” fires (direct emission within ∼5 s of production by the fire) that burned various biomass materials from the western US, δ15N–NOx ranges from −4.3 ‰ to +7.0 ‰, falling near the middle of the range reported in previous work. The first measurements of δ15N–HONO and δ18O–HONO in biomass burning smoke reveal a range of −5.3 ‰ to +5.8 ‰ and +5.2 ‰ to +15.2 ‰, respectively. Both HONO and NOx are sourced from N in the biomass fuel, and δ15N–HONO and δ15N–NOx are strongly correlated (R2=0.89, p<0.001), suggesting HONO is directly formed via subsequent chain reactions of NOx emitted from biomass combustion. Only 5 of 20 pNO3- samples had a sufficient amount for isotopic analysis and showed δ15N and δ18O of pNO3- ranging from −10.6 ‰ to −7.4 ‰ and +11.5 ‰ to +14.8 ‰, respectively. Our δ15N of NOx, HONO, and pNO3- ranges can serve as important biomass burning source signatures, useful for constraining emissions of these species in environmental applications. The δ18O of HONO and NO3- obtained here verify that our method is capable of determining the oxygen isotopic composition in BB plumes. The δ18O values for both of these species reflect laboratory conditions (i.e., a lack of photochemistry) and would be expected to track with the influence of different oxidation pathways in real environments. The methods used in this study will be further applied in future field studies to quantitatively track reactive nitrogen cycling in fresh and aged western US wildfire plumes.
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Meusel, Hannah, Alexandra Tamm, Uwe Kuhn, Dianming Wu, Anna Lena Leifke, Sabine Fiedler, Nina Ruckteschler et al. "Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus". Atmospheric Chemistry and Physics 18, n.º 2 (23 de enero de 2018): 799–813. http://dx.doi.org/10.5194/acp-18-799-2018.
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Abstract. Soil and biological soil crusts can emit nitrous acid (HONO) and nitric oxide (NO). The terrestrial ground surface in arid and semiarid regions is anticipated to play an important role in the local atmospheric HONO budget, deemed to represent one of the unaccounted-for HONO sources frequently observed in field studies. In this study HONO and NO emissions from a representative variety of soil and biological soil crust samples from the Mediterranean island Cyprus were investigated under controlled laboratory conditions. A wide range of fluxes was observed, ranging from 0.6 to 264 ng m−2 s−1 HONO-N at optimal soil water content (20–30 % of water holding capacity, WHC). Maximum NO-N fluxes at this WHC were lower (0.8–121 ng m−2 s−1). The highest emissions of both reactive nitrogen species were found from bare soil, followed by light and dark cyanobacteria-dominated biological soil crusts (biocrusts), correlating well with the sample nutrient levels (nitrite and nitrate). Extrapolations of lab-based HONO emission studies agree well with the unaccounted-for HONO source derived previously for the extensive CYPHEX field campaign, i.e., emissions from soil and biocrusts may essentially close the Cyprus HONO budget.
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Dyson, Joanna E., Graham A. Boustead, Lauren T. Fleming, Mark Blitz, Daniel Stone, Stephen R. Arnold, Lisa K. Whalley y Dwayne E. Heard. "Production of HONO from NO<sub>2</sub> uptake on illuminated TiO<sub>2</sub> aerosol particles and following the illumination of mixed TiO<sub>2</sub>∕ammonium nitrate particles". Atmospheric Chemistry and Physics 21, n.º 7 (16 de abril de 2021): 5755–75. http://dx.doi.org/10.5194/acp-21-5755-2021.
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Abstract. The rate of production of HONO from illuminated TiO2 aerosols in the presence of NO2 was measured using an aerosol flow tube system coupled to a photo-fragmentation laser-induced fluorescence detection apparatus. The reactive uptake coefficient of NO2 to form HONO, γNO2→HONO, was determined for NO2 mixing ratios in the range 34–400 ppb, with γNO2→HONO spanning the range (9.97 ± 3.52) × 10−6 to (1.26 ± 0.17) × 10−4 at a relative humidity of 15 ± 1 % and for a lamp photon flux of (1.63 ± 0.09) ×1016 photons cm−2 s−1 (integrated between 290 and 400 nm), which is similar to midday ambient actinic flux values. γNO2→HONO increased as a function of NO2 mixing ratio at low NO2 before peaking at (1.26 ± 0.17) ×10-4 at ∼ 51 ppb NO2 and then sharply decreasing at higher NO2 mixing ratios rather than levelling off, which would be indicative of surface saturation. The dependence of HONO production on relative humidity was also investigated, with a peak in production of HONO from TiO2 aerosol surfaces found at ∼ 25 % RH. Possible mechanisms consistent with the observed trends in both the HONO production and reactive uptake coefficient were investigated using a zero-dimensional kinetic box model. The modelling studies supported a mechanism for HONO production on the aerosol surface involving two molecules of NO2, as well as a surface HONO loss mechanism which is dependent upon NO2. In a separate experiment, significant production of HONO was observed from illumination of mixed nitrate/TiO2 aerosols in the absence of NO2. However, no production of HONO was seen from the illumination of nitrate aerosols alone. The rate of production of HONO observed from mixed nitrate/TiO2 aerosols was scaled to ambient conditions found at the Cape Verde Atmospheric Observatory (CVAO) in the remote tropical marine boundary layer. The rate of HONO production from aerosol particulate nitrate photolysis containing a photocatalyst was found to be similar to the missing HONO production rate necessary to reproduce observed concentrations of HONO at CVAO. These results provide evidence that particulate nitrate photolysis may have a significant impact on the production of HONO and hence NOx in the marine boundary layer where mixed aerosols containing nitrate and a photocatalytic species such as TiO2, as found in dust, are present.
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Zhang, Li, Qinyi Li, Tao Wang, Ravan Ahmadov, Qiang Zhang, Meng Li y Mengyao Lv. "Combined impacts of nitrous acid and nitryl chloride on lower-tropospheric ozone: new module development in WRF-Chem and application to China". Atmospheric Chemistry and Physics 17, n.º 16 (17 de agosto de 2017): 9733–50. http://dx.doi.org/10.5194/acp-17-9733-2017.
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Abstract. Nitrous acid (HONO) and nitryl chloride (ClNO2) – through their photolysis – can have profound effects on the nitrogen cycle and oxidation capacity of the lower troposphere. Previous numerical studies have separately considered and investigated the sources/processes of these compounds and their roles in the fate of reactive nitrogen and the production of ozone (O3), but their combined impact on the chemistry of the lower part of the troposphere has not been addressed yet. In this study, we updated the WRF-Chem model with the currently known sources and chemistry of HONO and chlorine in a new chemical mechanism (CBMZ_ReNOM), and applied it to a study of the combined effects of HONO and ClNO2 on summertime O3 in the boundary layer over China. We simulated the spatial distributions of HONO, ClNO2, and related compounds at the surface and within the lower troposphere. The results showed that the modeled HONO levels reached up to 800–1800 ppt at the surface (0–30 m) over the North China Plain (NCP), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) regions and that HONO was concentrated within a 0–200 m layer. In comparison, the simulated surface ClNO2 mixing ratio was around 800–1500 ppt over the NCP, YRD, and central China regions and was predominantly present in a 0–600 m layer. HONO enhanced daytime ROx (OH + HO2 + RO2) and O3 at the surface (0–30 m) by 2.8–4.6 ppt (28–37 %) and 2.9–6.2 ppb (6–13 %), respectively, over the three most developed regions, whereas ClNO2 increased surface O3 in the NCP and YRD regions by 2.4–3.3 ppb (or 5–6 %) and it also had a significant impact (3–6 %) on above-surface O3 within 200–500 m. The combined effects increased surface O3 by 11.5, 13.5, and 13.3 % in the NCP, YRD, and PRD regions, respectively. Over the boundary layer (0–1000 m), the HONO and ClNO2 enhanced O3 by up to 5.1 and 3.2 %, respectively, and their combined effect increased O3 by 7.1–8.9 % in the three regions. The new module noticeably improved O3 predictions at ∼ 900 monitoring stations throughout China by reducing the mean bias from −4.3 to 0.1 ppb. Our study suggests the importance of considering these reactive nitrogen species simultaneously into chemical transport models to better simulate the formation of summertime O3 in polluted regions.
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Yi, Hongming, Mathieu Cazaunau, Aline Gratien, Vincent Michoud, Edouard Pangui, Jean-Francois Doussin y Weidong Chen. "Intercomparison of IBBCEAS, NitroMAC and FTIR analyses for HONO, NO<sub>2</sub> and CH<sub>2</sub>O measurements during the reaction of NO<sub>2</sub> with H<sub>2</sub>O vapour in the simulation chamber CESAM". Atmospheric Measurement Techniques 14, n.º 8 (20 de agosto de 2021): 5701–15. http://dx.doi.org/10.5194/amt-14-5701-2021.
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Abstract. We report on applications of the ultraviolet-light-emitting-diode-based incoherent broadband cavity-enhanced absorption spectroscopy (UV-LED-IBBCEAS) technique for optical monitoring of HONO, NO2 and CH2O in a simulation chamber. Performance intercomparison of UV-LED-IBBCEAS with a wet chemistry-based NitroMAC sensor and a Fourier transform infrared (FTIR) spectrometer has been carried out on real-time simultaneous measurement of HONO, NO2 and CH2O concentrations during the reaction of NO2 with H2O vapour in CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber). The 1σ (signal-to-noise ratio (SNR) = 1) detection limits of 112 pptv for NO2, 56 pptv for HONO and 41 ppbv for CH2O over 120 s were found for the UV-LED-IBBCEAS measurement. On the contrary to many set-ups where cavities are installed outside the simulation chamber, we describe here an original in situ permanent installation. The intercomparison results demonstrate that IBBCEAS is a very well suitable technique for in situ simultaneous measurements of multiple chemically reactive species with high sensitivity and high precision even if the absorption bands of these species are overlapped. It offers excellent capacity for non-invasive optical monitoring of chemical reactions without any perturbation. For the application to simulation chambers, it has the advantage to provide a spatially integrated measurement across the reactor and hence to avoid point-sampling-related artefacts.
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Lane, Amanda E., Joanne T. M. Tan, Clare L. Hawkins, Alison K. Heather y Michael J. Davies. "The myeloperoxidase-derived oxidant HOSCN inhibits protein tyrosine phosphatases and modulates cell signalling via the mitogen-activated protein kinase (MAPK) pathway in macrophages". Biochemical Journal 430, n.º 1 (28 de julio de 2010): 161–69. http://dx.doi.org/10.1042/bj20100082.
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MPO (myeloperoxidase) catalyses the oxidation of chloride, bromide and thiocyanate by hydrogen peroxide to HOCl (hypochlorous acid), HOBr (hypobromous acid) and HOSCN (hypothiocyanous acid) respectively. Specificity constants indicate that SCN− is a major substrate for MPO. HOSCN is also a major oxidant generated by other peroxidases including salivary, gastric and eosinophil peroxidases. While HOCl and HOBr are powerful oxidizing agents, HOSCN is a less reactive, but more specific, oxidant which targets thiols and especially low pKa species. In the present study we show that HOSCN targets cysteine residues present in PTPs (protein tyrosine phosphatases) with this resulting in a loss of PTP activity for the isolated enzyme, in cell lysates and intact J774A.1 macrophage-like cells. Inhibition also occurs with MPO-generated HOCl and HOBr, but is more marked with MPO-generated HOSCN, particularly at longer incubation times. This inhibition is reversed by dithiothreitol, particularly at early time points, consistent with the reversible oxidation of the active site cysteine residue to give either a cysteine–SCN adduct or a sulfenic acid. Inhibition of PTP activity is associated with increased phosphorylation of p38a and ERK2 (extracellular-signal-regulated kinase 2) as detected by Western blot analysis and phosphoprotein arrays, and results in altered MAPK (mitogen-activated protein kinase) signalling. These data indicate that the highly selective targeting of some protein thiols by HOSCN can result in perturbation of cellular phosphorylation and altered cell signalling. These changes occur with (patho)physiological concentrations of SCN− ions, and implicate HOSCN as an important mediator of inflammation-induced oxidative damage, particularly in smokers who have elevated plasma levels of SCN−.
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Weber, Bettina, Dianming Wu, Alexandra Tamm, Nina Ruckteschler, Emilio Rodríguez-Caballero, Jörg Steinkamp, Hannah Meusel et al. "Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands". Proceedings of the National Academy of Sciences 112, n.º 50 (30 de noviembre de 2015): 15384–89. http://dx.doi.org/10.1073/pnas.1515818112.
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Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth’s nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a−1of NO-N and 0.6 Tg a−1of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.
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Roberts, T. J., R. S. Martin y L. Jourdain. "Reactive bromine chemistry in Mount Etna's volcanic plume: the influence of total Br, high-temperature processing, aerosol loading and plume–air mixing". Atmospheric Chemistry and Physics 14, n.º 20 (23 de octubre de 2014): 11201–19. http://dx.doi.org/10.5194/acp-14-11201-2014.
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Abstract. Volcanic emissions present a source of reactive halogens to the troposphere, through rapid plume chemistry that converts the emitted HBr to more reactive forms such as BrO. The nature of this process is poorly quantified, yet is of interest in order to understand volcanic impacts on the troposphere, and infer volcanic activity from volcanic gas measurements (i.e. BrO / SO2 ratios). Recent observations from Etna report an initial increase and subsequent plateau or decline in BrO / SO2 ratios with distance downwind. We present daytime PlumeChem model simulations that reproduce and explain the reported trend in BrO / SO2 at Etna including the initial rise and subsequent plateau. Suites of model simulations also investigate the influences of volcanic aerosol loading, bromine emission, and plume–air mixing rate on the downwind plume chemistry. Emitted volcanic HBr is converted into reactive bromine by autocatalytic bromine chemistry cycles whose onset is accelerated by the model high-temperature initialisation. These rapid chemistry cycles also impact the reactive bromine speciation through inter-conversion of Br, Br2, BrO, BrONO2, BrCl, HOBr. We predict a new evolution of Br speciation in the plume. BrO, Br2, Br and HBr are the main plume species near downwind whilst BrO and HOBr are present further downwind (where BrONO2 and BrCl also make up a minor fraction). BrNO2 is predicted to be only a relatively minor plume component. The initial rise in BrO / SO2 occurs as ozone is entrained into the plume whose reaction with Br promotes net formation of BrO. Aerosol has a modest impact on BrO / SO2 near-downwind (< ~6 km, ~10 min) at the relatively high loadings considered. The subsequent decline in BrO / SO2 occurs as entrainment of oxidants HO2 and NO2 promotes net formation of HOBr and BrONO2, whilst the plume dispersion dilutes volcanic aerosol so slows the heterogeneous loss rates of these species. A higher volcanic aerosol loading enhances BrO / SO2 in the (> 6 km) downwind plume. Simulations assuming low/medium and high Etna bromine emissions scenarios show that the bromine emission has a greater influence on BrO / SO2 further downwind and a modest impact near downwind, and show either complete or partial conversion of HBr into reactive bromine, respectively, yielding BrO contents that reach up to ~50 or ~20% of total bromine (over a timescale of a few 10 s of minutes). Plume–air mixing non-linearly impacts the downwind BrO / SO2, as shown by simulations with varying plume dispersion, wind speed and volcanic emission flux. Greater volcanic emission flux leads to lower BrO / SO2 ratios near downwind, but also delays the subsequent decline in BrO / SO2, and thus yields higher BrO / SO2 ratios further downwind. We highlight the important role of plume chemistry models for the interpretation of observed changes in BrO / SO2 during/prior to volcanic eruptions, as well as for quantifying volcanic plume impacts on atmospheric chemistry. Simulated plume impacts include ozone, HOx and NOx depletion, the latter converted into HNO3. Partial recovery of ozone occurs with distance downwind, although cumulative ozone loss is ongoing over the 3 h simulations.
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Roberts, James M., Chelsea E. Stockwell, Robert J. Yokelson, Joost de Gouw, Yong Liu, Vanessa Selimovic, Abigail R. Koss et al. "The nitrogen budget of laboratory-simulated western US wildfires during the FIREX 2016 Fire Lab study". Atmospheric Chemistry and Physics 20, n.º 14 (24 de julio de 2020): 8807–26. http://dx.doi.org/10.5194/acp-20-8807-2020.
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Abstract. Reactive nitrogen (Nr, defined as all nitrogen-containing compounds except for N2 and N2O) is one of the most important classes of compounds emitted from wildfire, as Nr impacts both atmospheric oxidation processes and particle formation chemistry. In addition, several Nr compounds can contribute to health impacts from wildfires. Understanding the impacts of wildfire on the atmosphere requires a thorough description of Nr emissions. Total reactive nitrogen was measured by catalytic conversion to NO and detection by NO–O3 chemiluminescence together with individual Nr species during a series of laboratory fires of fuels characteristic of western US wildfires, conducted as part of the FIREX Fire Lab 2016 study. Data from 75 stack fires were analyzed to examine the systematics of nitrogen emissions. The measured Nr ∕ total-carbon ratios averaged 0.37 % for fuels characteristic of western North America, and these gas-phase emissions were compared with fuel and residue N∕C ratios and mass to estimate that a mean (±SD) of 0.68 (±0.14) of fuel nitrogen was emitted as N2 and N2O. The Nr detected as speciated individual compounds included the following: nitric oxide (NO), nitrogen dioxide (NO2), nitrous acid (HONO), isocyanic acid (HNCO), hydrogen cyanide (HCN), ammonia (NH3), and 44 nitrogen-containing volatile organic compounds (NVOCs). The sum of these measured individual Nr compounds averaged 84.8 (±9.8) % relative to the total Nr, and much of the 15.2 % “unaccounted” Nr is expected to be particle-bound species, not included in this analysis. A number of key species, e.g., HNCO, HCN, and HONO, were confirmed not to correlate with only flaming or with only smoldering combustion when using modified combustion efficiency, MCE=CO2/(CO+CO2), as a rough indicator. However, the systematic variations in the abundance of these species relative to other nitrogen-containing species were successfully modeled using positive matrix factorization (PMF). Three distinct factors were found for the emissions from combined coniferous fuels: a combustion factor (Comb-N) (800–1200 ∘C) with emissions of the inorganic compounds NO, NO2, and HONO, and a minor contribution from organic nitro compounds (R-NO2); a high-temperature pyrolysis factor (HT-N) (500–800 ∘C) with emissions of HNCO, HCN, and nitriles; and a low-temperature pyrolysis factor (LT-N) (<500 ∘C) with mostly ammonia and NVOCs. The temperature ranges specified are based on known combustion and pyrolysis chemistry considerations. The mix of emissions in the PMF factors from chaparral fuels (manzanita and chamise) had a slightly different composition: the Comb-N factor was also mostly NO, with small amounts of HNCO, HONO, and NH3; the HT-N factor was dominated by NO2 and had HONO, HCN, and HNCO; and the LT-N factor was mostly NH3 with a slight amount of NO contributing. In both cases, the Comb-N factor correlated best with CO2 emission, while the HT-N factors from coniferous fuels correlated closely with the high-temperature VOC factors recently reported by Sekimoto et al. (2018), and the LT-N had some correspondence to the LT-VOC factors. As a consequence, CO2 is recommended as a marker for combustion Nr emissions, HCN is recommended as a marker for HT-N emissions, and the family NH3 ∕ particle ammonium is recommended as a marker for LT-N emissions.
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Abduvokhidov, Davronjon, Maksudbek Yusupov, Aamir Shahzad, Pankaj Attri, Masaharu Shiratani, Maria C. Oliveira y Jamoliddin Razzokov. "Unraveling the Transport Properties of RONS across Nitro-Oxidized Membranes". Biomolecules 13, n.º 7 (27 de junio de 2023): 1043. http://dx.doi.org/10.3390/biom13071043.
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The potential of cold atmospheric plasma (CAP) in biomedical applications has received significant interest, due to its ability to generate reactive oxygen and nitrogen species (RONS). Upon exposure to living cells, CAP triggers alterations in various cellular components, such as the cell membrane. However, the permeation of RONS across nitrated and oxidized membranes remains understudied. To address this gap, we conducted molecular dynamics simulations, to investigate the permeation capabilities of RONS across modified cell membranes. This computational study investigated the translocation processes of less hydrophilic and hydrophilic RONS across the phospholipid bilayer (PLB), with various degrees of oxidation and nitration, and elucidated the impact of RONS on PLB permeability. The simulation results showed that less hydrophilic species, i.e., NO, NO2, N2O4, and O3, have a higher penetration ability through nitro-oxidized PLB compared to hydrophilic RONS, i.e., HNO3, s-cis-HONO, s-trans-HONO, H2O2, HO2, and OH. In particular, nitro-oxidation of PLB, induced by, e.g., cold atmospheric plasma, has minimal impact on the penetration of free energy barriers of less hydrophilic species, while it lowers these barriers for hydrophilic RONS, thereby enhancing their translocation across nitro-oxidized PLB. This research contributes to a better understanding of the translocation abilities of RONS in the field of plasma biomedical applications and highlights the need for further analysis of their role in intracellular signaling pathways.
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Bourgeois, Ilann, Jeff Peischl, J. Andrew Neuman, Steven S. Brown, Hannah M. Allen, Pedro Campuzano-Jost, Matthew M. Coggon et al. "Comparison of airborne measurements of NO, NO2, HONO, NOy, and CO during FIREX-AQ". Atmospheric Measurement Techniques 15, n.º 16 (29 de agosto de 2022): 4901–30. http://dx.doi.org/10.5194/amt-15-4901-2022.
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Abstract. We present a comparison of fast-response instruments installed onboard the NASA DC-8 aircraft that measured nitrogen oxides (NO and NO2), nitrous acid (HONO), total reactive odd nitrogen (measured both as the total (NOy) and from the sum of individually measured species (ΣNOy)), and carbon monoxide (CO) in the troposphere during the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign. By targeting smoke from summertime wildfires, prescribed fires, and agricultural burns across the continental United States, FIREX-AQ provided a unique opportunity to investigate measurement accuracy in concentrated plumes where hundreds of species coexist. Here, we compare NO measurements by chemiluminescence (CL) and laser-induced fluorescence (LIF); NO2 measurements by CL, LIF, and cavity-enhanced spectroscopy (CES); HONO measurements by CES and iodide-adduct chemical ionization mass spectrometry (CIMS); and CO measurements by tunable diode laser absorption spectrometry (TDLAS) and integrated cavity output spectroscopy (ICOS). Additionally, total NOy measurements using the CL instrument were compared with ΣNOy (= NO + NO2 + HONO + nitric acid (HNO3) + acyl peroxy nitrates (APNs) + submicrometer particulate nitrate (pNO3)). Other NOy species were not included in ΣNOy as they either contributed minimally to it (e.g., C1–C5 alkyl nitrates, nitryl chloride (ClNO2), dinitrogen pentoxide (N2O5)) or were not measured during FIREX-AQ (e.g., higher oxidized alkyl nitrates, nitrate (NO3), non-acyl peroxynitrates, coarse-mode aerosol nitrate). The aircraft instrument intercomparisons demonstrate the following points: (1) NO measurements by CL and LIF agreed well within instrument uncertainties but with potentially reduced time response for the CL instrument; (2) NO2 measurements by LIF and CES agreed well within instrument uncertainties, but CL NO2 was on average 10 % higher; (3) CES and CIMS HONO measurements were highly correlated in each fire plume transect, but the correlation slope of CES vs. CIMS for all 1 Hz data during FIREX-AQ was 1.8, which we attribute to a reduction in the CIMS sensitivity to HONO in high-temperature environments; (4) NOy budget closure was demonstrated for all flights within the combined instrument uncertainties of 25 %. However, we used a fluid dynamic flow model to estimate that average pNO3 sampling fraction through the NOy inlet in smoke was variable from one flight to another and ranged between 0.36 and 0.99, meaning that approximately 0 %–24 % on average of the total measured NOy in smoke may have been unaccounted for and may be due to unmeasured species such as organic nitrates; (5) CO measurements by ICOS and TDLAS agreed well within combined instrument uncertainties, but with a systematic offset that averaged 2.87 ppbv; and (6) integrating smoke plumes followed by fitting the integrated values of each plume improved the correlation between independent measurements.
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Hoch, D. J., J. Buxmann, H. Sihler, D. Pöhler, C. Zetzsch y U. Platt. "An instrument for measurements of BrO with LED-based Cavity-Enhanced Differential Optical Absorption Spectroscopy". Atmospheric Measurement Techniques 7, n.º 1 (27 de enero de 2014): 199–214. http://dx.doi.org/10.5194/amt-7-199-2014.
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Abstract. The chemistry of the troposphere and specifically the global tropospheric ozone budget is affected by reactive halogen species such as bromine monoxide (BrO) or chlorine monoxide (ClO). Especially BrO plays an important role in the processes of ozone destruction, disturbance of NOx and HOx chemistry, oxidation of dimethyl sulfide (DMS), and the deposition of elementary mercury. In the troposphere BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer. For a better understanding of these processes, field measurements as well as reaction chamber studies are performed. In both cases instruments with high spatial resolution and high sensitivity are necessary. A Cavity-Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument with an open path measurement cell was designed and applied. For the first time, a CE-DOAS instrument is presented using an UV LED in the 325–365 nm wavelength range. In laboratory studies, BrO as well as HONO, HCHO, O3, and O4 could be reliably determined at detection limits of 20 ppt for BrO, 9.1 ppb for HCHO, 970 ppt for HONO, and 91 ppb for O3, for five minutes integration time. The best detection limits were achieved for BrO (11 ppt), HCHO (5.1 ppb), HONO (490 ppt), and O3 (59 ppb) for integration times of 81 minutes or less. Comparison with established White system (WS) DOAS and O3 monitor measurements demonstrate the reliability of the instrument.
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Hoch, D. J., J. Buxmann, H. Sihler, D. Pöhler, C. Zetzsch y U. Platt. "A novel instrument for measurements of BrO with LED based Cavity-Enhanced Differential Optical Absorption Spectoscopy". Atmospheric Measurement Techniques Discussions 6, n.º 4 (2 de julio de 2013): 6047–96. http://dx.doi.org/10.5194/amtd-6-6047-2013.
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Abstract. The chemistry of the troposphere and specifically the global tropospheric ozone budget is affected by reactive halogen species like Bromine monoxide (BrO) or Chlorine monoxide (ClO). Especially BrO plays an important role in the processes of ozone destruction, disturbance of NOx and HOx chemistry, oxidation of DMS, and the deposition of elementary mercury. In the troposphere BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer. For a better understanding of these processes field measurements as well as reaction-chamber studies are performed. In both cases instruments with high spatial resolution and high sensitivity are necessary. A Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument with an open path measurement cell was designed and applied. For the first time, a CE-DOAS instrument is presented using an UV-LED in the 325–365 nm wavelength range. In laboratory studies, BrO as well as HONO, HCHO, O3, and O4, could be reliable determined at detection limits of 20 ppt for BrO, 9.1 ppb for HCHO, 970 ppt for HONO, and 91 ppb for O3, for five minutes integration time, respectively. The best detection limits were achieved for BrO (11 ppt), HCHO (5.1 ppb), HONO (490 ppt), and O3 (59 ppb) for integration times of 81 min or less. Comparison with established White-System DOAS and O3 monitor demonstrate the reliability of the instrument.
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Roberts, T. J., R. S. Martin y L. Jourdain. "Reactive bromine chemistry in Mt. Etna's volcanic plume: the influence of total Br, high temperature processing, aerosol loading and plume-air mixing". Atmospheric Chemistry and Physics Discussions 14, n.º 5 (3 de marzo de 2014): 5445–94. http://dx.doi.org/10.5194/acpd-14-5445-2014.
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Abstract. Volcanic emissions present a source of reactive halogens to the troposphere, through rapid plume chemistry that converts the emitted HBr to more reactive forms such as BrO. The nature of this process is poorly quantified, yet is of interest to understand volcanic impacts on the troposphere, and infer volcanic activity from volcanic gas measurements (i.e. BrO / SO2 ratios). Recent observations from Etna report an initial increase and subsequent plateau or decline in BrO / SO2 ratios with distance downwind. We present daytime PlumeChem model simulations that reproduce and explain the reported trend in BrO / SO2 at Etna including the initial rise and subsequent plateau. Through suites of model simulations we also investigate the influences of volcanic aerosol loading, bromine emission, and plume-air mixing rate on the downwind plume chemistry. Emitted volcanic HBr is converted into reactive bromine by autocatalytic bromine chemistry cycles whose onset is accelerated by the model high-temperature initialisation. These rapid chemistry cycles also impact the reactive bromine speciation through inter-conversion of Br, Br2, BrO, BrONO2, BrCl, HOBr. Formation of BrNO2 is also discussed. We predict a new evolution of Br-speciation in the plume, with BrO, Br2, Br and HBr as the main plume species in the near downwind plume whilst BrO, and HOBr are present in significant quantities further downwind (where BrONO2 and BrCl also make up a minor fraction). The initial rise in BrO / SO2 occurs as ozone is entrained into the plume whose reaction with Br promotes net formation of BrO. Aerosol has a modest impact on BrO / SO2 near-downwind (< 6 km) at the relatively high loadings considered. The subsequent decline in BrO / SO2 occurs as entrainment of oxidants HO2 and NO2 promotes net formation of HOBr and BrONO2, whilst the plume dispersion dilutes volcanic aerosol so slows the heterogeneous loss rates of these species. A higher volcanic aerosol loading enhances BrO / SO2 in the (> 6 km) downwind plume. Simulations assuming low/medium and high Etna bromine emissions scenarios show the bromine emission has a greater influence on BrO / SO2 further downwind and a modest impact near downwind, and show either complete or partial conversion of HBr into reactive bromine, respectively, yielding BrO contents that reach up to ∼50% or ∼20% of total bromine (over a timescale of a few 10's of minutes). Plume-air mixing (which in our model with fixed plume dimensions is inversely related to the volcanic emission flux) non-linearly impacts the downwind BrO / SO2. A slower rate of plume-air mixing (or greater volcanic emission flux) leads to lower BrO / SO2 ratios near downwind, but also delays the subsequent decline in BrO / SO2, thus yields higher BrO / SO2 ratios further downwind. We highlight the important role of plume chemistry models for the interpretation of observed changes in BrO / SO2 during/prior to volcanic eruptions, as well as for quantifying volcanic plume impacts on atmospheric chemistry. Simulated plume impacts include ozone, HOx and NOx depletion, the latter converted into HNO3. Partial recovery of ozone concentrations occurs with distance downwind (as BrO concentrations decline), although cumulative ozone loss is ongoing over the 3 h simulations. We suggest plume BrNO2 may be less prevalent than previous model predictions. We highlight additional reactions for BrNO2 (and alternative pathways via BrONO) which likely reduce in-plume BrNO2 prevalence. We also highlight uncertainty in volcanic NOx emissions that might be lower than previously assumed (i.e., equilibrium NOx), due to the slow rate of N2 oxidation. The atmospheric : magmatic gas ratio, VA : VM, in equilibrium model representations of the near vent plume is presently poorly defined. Using a revised equilibrium model methodology, lower VA : VM become suitable (e.g. VA : VM = 98 : 2, 95 : 5), which also yield a lower estimate for volcanic NOx, although uncertainties to such equilibrium model representations of near-vent plume chemistry and especially NOx formation are emphasized.
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Toyota, K., J. C. McConnell, R. M. Staebler y A. P. Dastoor. "Air–snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 1: In-snow bromine activation and its impact on ozone". Atmospheric Chemistry and Physics 14, n.º 8 (25 de abril de 2014): 4101–33. http://dx.doi.org/10.5194/acp-14-4101-2014.
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Abstract. To provide a theoretical framework towards a better understanding of ozone depletion events (ODEs) and atmospheric mercury depletion events (AMDEs) in the polar boundary layer, we have developed a one-dimensional model that simulates multiphase chemistry and transport of trace constituents from porous snowpack and through the atmospheric boundary layer (ABL) as a unified system. This paper constitutes Part 1 of the study, describing a general configuration of the model and the results of simulations related to reactive bromine release from the snowpack and ODEs during the Arctic spring. A common set of aqueous-phase reactions describes chemistry both within the liquid-like layer (LLL) on the grain surface of the snowpack and within deliquesced "haze" aerosols mainly composed of sulfate in the atmosphere. Gas-phase reactions are also represented by the same mechanism in the atmosphere and in the snowpack interstitial air (SIA). Consequently, the model attains the capacity of simulating interactions between chemistry and mass transfer that become particularly intricate near the interface between the atmosphere and the snowpack. In the SIA, reactive uptake on LLL-coated snow grains and vertical mass transfer act simultaneously on gaseous HOBr, a fraction of which enters from the atmosphere while another fraction is formed via gas-phase chemistry in the SIA itself. A "bromine explosion", by which HOBr formed in the ambient air is deposited and then converted heterogeneously to Br2, is found to be a dominant process of reactive bromine formation in the top 1 mm layer of the snowpack. Deeper in the snowpack, HOBr formed within the SIA leads to an in-snow bromine explosion, but a significant fraction of Br2 is also produced via aqueous radical chemistry in the LLL on the surface of the snow grains. These top- and deeper-layer productions of Br2 both contribute to the release of Br2 to the atmosphere, but the deeper-layer production is found to be more important for the net outflux of reactive bromine. Although ozone is removed via bromine chemistry, it is also among the key species that control both the conventional and in-snow bromine explosions. On the other hand, aqueous-phase radical chemistry initiated by photolytic OH formation in the LLL is also a significant contributor to the in-snow source of Br2 and can operate without ozone, whereas the delivery of Br2 to the atmosphere becomes much smaller after ozone is depleted. Catalytic ozone loss via bromine radical chemistry occurs more rapidly in the SIA than in the ambient air, giving rise to apparent dry deposition velocities for ozone from the air to the snow on the order of 10−3 cm s−1 during daytime. Overall, however, the depletion of ozone in the system is caused predominantly by ozone loss in the ambient air. Increasing depth of the turbulent ABL under windy conditions will delay the buildup of reactive bromine and the resultant loss of ozone, while leading to the higher column amount of BrO in the atmosphere. During the Arctic spring, if moderately saline and acidic snowpack is as prevalent as assumed in our model runs on sea ice, the shallow, stable ABL under calm weather conditions may undergo persistent ODEs without substantial contributions from blowing/drifting snow and wind-pumping mechanisms, whereas the column densities of BrO in the ABL will likely remain too low in the course of such events to be detected unambiguously by satellite nadir measurements.
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Buxmann, Joelle, Sergej Bleicher, Ulrich Platt, Roland von Glasow, Roberto Sommariva, Andreas Held, Cornelius Zetzsch y Johannes Ofner. "Consumption of reactive halogen species from sea-salt aerosol by secondary organic aerosol: slowing down the bromine explosion". Environmental Chemistry 12, n.º 4 (2015): 476. http://dx.doi.org/10.1071/en14226.
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Environmental context Secondary organic aerosols together with sea-salt aerosols are a major contribution to global aerosols and influence the release of reactive halogens, which affect air quality and human health. In this study, the loss of reactive halogen species from simulated salt aerosols due to three different types of secondary organic aerosols was quantified in chamber experiments and investigated with the help of a numerical model. The loss rate can be included into chemistry models of the atmosphere and help to quantify the halogen budget in nature. Abstract The interaction between secondary organic aerosols (SOAs) and reactive bromine species (e.g. BrO, Br2, HOBr) coexisting in the environment is not well understood and not included in current chemistry models. The present study quantifies the quenching of bromine release from an artificial salt aerosol caused by SOAs from ozonolysis of three precursors (α-pinene, catechol or guaiacol) in a Teflon smog chamber and incorporates it into a chemical box model. The model simulations perform very well for a blank experiment without SOA precursor, capturing BrO formation, as detected by differential optical absorption spectrometry. A first-order BrO loss rate of 0.001s–1 on the surface of SOA represents the overall effective Brx (total inorganic bromine) loss included in the model. Generally, the model agrees with the maximum BrO mixing ratio in time and magnitude, with some disagreements in the exact shape. Formation of reactive OClO was observed in the presence of organics but could not be reproduced by the model. According to current knowledge, most inorganic chlorine would be in the form of HCl in the presence of organics, as predicted by the model. In order to reproduce the net effects of the presence of SOA, the effective uptake coefficients of reactive bromine on the SOA surface are estimated to be 0.01, 0.01 and 0.004 for α-pinene, catechol and guaiacol respectively. The uptake coefficient can now be incorporated into box models and even global models, where sinks for bromine species are thought to be inadequately represented.
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Voigt, C., U. Schumann, T. Jurkat, D. Schäuble, H. Schlager, A. Petzold, J. F. Gayet et al. "In-situ observations of young contrails – overview and selected results from the CONCERT campaign". Atmospheric Chemistry and Physics 10, n.º 18 (30 de septiembre de 2010): 9039–56. http://dx.doi.org/10.5194/acp-10-9039-2010.
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Abstract. Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. The Falcon was equipped with a set of instruments to measure the particle size distribution, shape, extinction and chemical composition as well as trace gas mixing ratios of sulfur dioxide (SO2), reactive nitrogen and halogen species (NO, NOy, HNO3, HONO, HCl), ozone (O3) and carbon monoxide (CO). During 12 mission flights over Europe, numerous contrails, cirrus clouds and a volcanic aerosol layer were probed at altitudes between 8.5 and 11.6 km and at temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. On 19 November 2008 the contrail from a CRJ-2 aircraft was penetrated in 10.1 km altitude at a temperature of 221 K. The contrail had mean ice crystal number densities of 125 cm−3 with effective radii reff of 2.6 μm. The presence of particles with r>50 μm in the less than 2 min old contrail suggests that natural cirrus crystals were entrained in the contrail. Mean HONO/NO (HONO/NOy) ratios of 0.037 (0.024) and the fuel sulfur conversion efficiency to H2SO4 (εS↓) of 2.9 % observed in the CRJ-2 contrail are in the range of previous measurements in the gaseous aircraft exhaust. On 31 October 2010 aviation NO emissions could have contributed by more than 40% to the regional scale NO levels in the mid-latitude lowest stratosphere. The CONCERT observations help to better quantify the climate impact from contrails and will be used to investigate the chemical processing of trace gases on contrails.
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Friedrich, Nils, Philipp Eger, Justin Shenolikar, Nicolas Sobanski, Jan Schuladen, Dirk Dienhart, Bettina Hottmann et al. "Reactive nitrogen around the Arabian Peninsula and in the Mediterranean Sea during the 2017 AQABA ship campaign". Atmospheric Chemistry and Physics 21, n.º 10 (18 de mayo de 2021): 7473–98. http://dx.doi.org/10.5194/acp-21-7473-2021.
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Abstract. We present shipborne measurements of NOx (≡ NO + NO2) and NOy (≡ NOx+ gas- and particle-phase organic and inorganic oxides of nitrogen) in summer 2017 as part of the expedition “Air Quality and climate change in the Arabian BAsin” (AQABA). The NOx and NOz (≡ NOy-NOx) measurements, made with a thermal dissociation cavity ring-down spectrometer (TD-CRDS), were used to examine the chemical mechanisms involved in the processing of primary NOx emissions and their influence on the NOy budget in chemically distinct marine environments, including the Mediterranean Sea, the Red Sea, and the Arabian Gulf, which were influenced to varying extents by emissions from shipping and oil and gas production. Complementing the TD-CRDS measurements, NO and NO2 data sets from a chemiluminescence detector (CLD) were used in the analysis. In all regions, we find that NOx is strongly connected to ship emissions, both via direct emission of NO and via the formation of HONO and its subsequent photolytic conversion to NO. The role of HONO was assessed by calculating the NOx production rate from its photolysis. Mean NO2 lifetimes were 3.9 h in the Mediterranean Sea, 4.0 h in the Arabian Gulf, and 5.0 h in the Red Sea area. The cumulative loss of NO2 during the night (reaction with O3) was more important than daytime losses (reaction with OH) over the Arabian Gulf (by a factor 2.8) and over the Red Sea (factor 2.9), whereas over the Mediterranean Sea, where OH levels were high, daytime losses dominated (factor 2.5). Regional ozone production efficiencies (OPEs; calculated from the correlation between Ox and NOz, where Ox= O3+ NO2) ranged from 10.5 ± 0.9 to 19.1 ± 1.1. This metric quantifies the relative strength of photochemical O3 production from NOx compared to the competing sequestering into NOz species. The largest values were found over the Arabian Gulf, consistent with high levels of O3 found in that region (10–90 percentiles range: 23–108 ppbv). The fractional contribution of individual NOz species to NOy exhibited a large regional variability, with HNO3 generally the dominant component (on average 33 % of NOy) with significant contributions from organic nitrates (11 %) and particulate nitrates in the PM1 size range (8 %).
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Wren, S. N., D. J. Donaldson y J. P. D. Abbatt. "Photochemical chlorine and bromine activation from artificial saline snow". Atmospheric Chemistry and Physics Discussions 13, n.º 5 (30 de mayo de 2013): 14163–93. http://dx.doi.org/10.5194/acpd-13-14163-2013.
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Abstract. The activation of reactive halogen species – particularly Cl2 – from sea ice and snow surfaces is not well understood. In this study, we used a photochemical snow reactor coupled to a chemical ionization mass spectrometer to investigate the production of Br2, BrCl and Cl2 from NaCl/NaBr-doped artificial snow samples. At temperatures above the NaCl-water eutectic, illumination of samples (λ > 310 nm) in the presence of gas phase O3 led to the accelerated release of Br2, BrCl and the release of Cl2 in a process that was significantly enhanced by acidity, high surface area and additional gas phase Br2. Cl2 production was only observed when both light and ozone were present. The total halogen release depended on [O3] and pre-freezing [NaCl]. Our observations support a "halogen explosion" mechanism occurring within the snowpack which is initiated by heterogeneous oxidation, and propagated by Br2 or BrCl photolysis and by recycling of HOBr and HOCl into the snowpack. Our study implicates an important role for active chemistry occurring within the interstitial air of aged (i.e., acidic) snow for halogen activation at polar sunrise.
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Wren, S. N., D. J. Donaldson y J. P. D. Abbatt. "Photochemical chlorine and bromine activation from artificial saline snow". Atmospheric Chemistry and Physics 13, n.º 19 (7 de octubre de 2013): 9789–800. http://dx.doi.org/10.5194/acp-13-9789-2013.
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Abstract. The activation of reactive halogen species – particularly Cl2 – from sea ice and snow surfaces is not well understood. In this study, we used a photochemical snow reactor coupled to a chemical ionization mass spectrometer to investigate the production of Br2, BrCl and Cl2 from NaCl/NaBr-doped artificial snow samples. At temperatures above the NaCl-water eutectic, illumination of samples (λ > 310 nm) in the presence of gas phase O3 led to the accelerated release of Br2, BrCl and the release of Cl2 in a process that was significantly enhanced by acidity, high surface area and additional gas phase Br2. Cl2 production was only observed when both light and ozone were present. The total halogen release depended on [ozone] and pre-freezing [NaCl]. Our observations support a "halogen explosion" mechanism occurring within the snowpack, which is initiated by heterogeneous oxidation and propagated by Br2 or BrCl photolysis and by recycling of HOBr and HOCl into the snowpack. Our study implicates this important role of active chemistry occurring within the interstitial air of aged (i.e. acidic) snow for halogen activation at polar sunrise.
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Galtier, Sandrine, Clément Pivard y Patrick Rairoux. "Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases". Remote Sensing 12, n.º 20 (20 de octubre de 2020): 3444. http://dx.doi.org/10.3390/rs12203444.
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The development of increasingly sensitive and robust instruments and new methodologies are essential to improve our understanding of the Earth’s climate and air pollution. In this context, Dual-Comb spectroscopy (DCS) has been successfully demonstrated as a remote laser-based instrument to probe infrared absorbing species such as greenhouse gases. We present here a study of the sensitivity of Dual-Comb spectroscopy to remotely monitor atmospheric gases focusing on molecules that absorb in the ultraviolet domain, where the most reactive molecules of the atmosphere (OH, HONO, BrO...) have their highest absorption cross-sections. We assess the achievable signal-to-noise ratio (SNR) and the corresponding minimum absorption sensitivity of DCS in the ultraviolet range. We propose a potential light source for remote sensing UV-DCS and discuss the degree of immunity of UV-DCS to atmospheric turbulences. We show that the characteristics of the currently available UV sources are compatible with the unambiguous identification of UV absorbing gases by UV-DCS.
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Cao, L., H. Sihler, U. Platt y E. Gutheil. "Numerical analysis of the chemical kinetic mechanisms of ozone depletion and halogen release in the polar troposphere". Atmospheric Chemistry and Physics Discussions 13, n.º 9 (13 de septiembre de 2013): 24171–222. http://dx.doi.org/10.5194/acpd-13-24171-2013.
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Abstract. In recent years, the role of halogen species (e.g. Br, Cl) in the troposphere of polar regions is investigated after the discovery of their importance for boundary layer ozone destruction in the polar spring. Halogen species take part in an auto-catalytic chemical cycle including key self reactions. In this study, several chemical reaction schemes are investigated, and the importance of specific reactions and their rate constants is identified by a sensitivity analysis. A category of heterogeneous reactions related to HOBr activate halogen ions from sea salt aerosols, fresh sea ice or snow pack, driving the "bromine explosion". In the Arctic, a small amount of NOx may exist, which comes from nitrate contained in the snow, and this NOx may have a strong impact on ozone depletion. The heterogeneous reaction rates are parameterized by considering the aerodynamic resistance, a reactive surface ratio, β, i.e. ratio of reactive surface area to total ground surface area, and the boundary layer height, Lmix. It is found that for β = 1, the ozone depletion process starts after five days and lasts for 40 h for Lmix = 200 m. Ozone depletion duration becomes independent of the height of the boundary layer for about β≥20, and it approaches a value of two days for β=100. The role of nitrogen and chlorine containing species on the ozone depletion rate is studied. The calculation of the time integrated bromine and chlorine atom concentrations suggests a value in the order of 103 for the [Br] / [Cl] ratio, which reveals that atomic chlorine radicals have minor direct influence on the ozone depletion. The NOx concentrations are influenced by different chemical cycles over different time periods. During ozone depletion, the reaction cycle involving the BrONO2 hydrolysis is dominant. A critical value of 0.002 of the uptake coefficient of the BrONO2 hydrolysis reaction at the aerosol and saline surfaces is identified, beyond which the existence of NOx species accelerate the ozone depletion event – for lower values, deceleration occurs.
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Liao, J., L. G. Huey, D. J. Tanner, S. Brooks, J. E. Dibb, J. Stutz, J. L. Thomas, B. Lefer, C. Haman y K. Gorham. "Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008". Atmospheric Chemistry and Physics Discussions 11, n.º 4 (26 de abril de 2011): 12725–62. http://dx.doi.org/10.5194/acpd-11-12725-2011.
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Abstract. The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring~2007 and summer~2008 to investigate the impact of halogens on HOx (=OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + ROx), ozone (O3), nitrogen oxide (NO), nitric acid (HNO2), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm−3 and 3.0 × 106 molec cm−3 in spring 2007, and 4.2 × 108 molec cm−3 and 4.1 × 106 molec cm−3 in summer~2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly change the predictions. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2+RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.
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Morin, S., R. Sander y J. Savarino. "Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species". Atmospheric Chemistry and Physics Discussions 10, n.º 12 (14 de diciembre de 2010): 30405–51. http://dx.doi.org/10.5194/acpd-10-30405-2010.
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Abstract. The isotope anomaly (Δ17O) of secondary atmospheric species such as nitrate (NO3−) or hydrogen peroxyde (H2O2) has potential to provide useful constrains on their formation pathways. Indeed, the Δ17O of their precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ17O in the atmosphere. Interpreting variations of Δ17O in secondary species requires an in-depth understanding of the Δ17O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. We present results from numerical simulations carried out using the atmospheric chemistry box model (CAABA/MECCA) to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NOx and HOx. Δ17O was propagated from ozone to other species (NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the classical mass-balance equation, through the implementation of various sets of hypotheses pertaining to the transfer of Δ17O during chemical reactions. The model confirms that diurnal variations in Δ17O of NOx are well predicted by the photochemical steady-state relationship during the day, but that at night a different approach must be employed (i.e. "fossilization" of the Δ17O of NOx as soon as the photolytical lifetime of NOx drops below ca. 5 min). We quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H2O2 under the various environmental conditions analyzed, which is of particular relevance to larger-scale implementations of Δ17O where high computational costs cannot be afforded.
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Toyota, K., J. C. McConnell, R. M. Staebler y A. P. Dastoor. "Air-snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 1: In-snow bromine activation and its impact on ozone". Atmospheric Chemistry and Physics Discussions 13, n.º 8 (5 de agosto de 2013): 20341–418. http://dx.doi.org/10.5194/acpd-13-20341-2013.
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Abstract. To provide a theoretical framework towards better understanding of ozone depletion events (ODEs) and atmospheric mercury depletion events (AMDEs) in the polar boundary layer, we have developed a one-dimensional model that simulates multiphase chemistry and transport of trace constituents from porous snowpack and through the atmospheric boundary layer (ABL) as a unified system. In this paper, we describe a general configuration of the model and the results of simulations related to reactive bromine release from the snowpack and ODEs during the Arctic spring. The model employs a chemical mechanism adapted from the one previously used for the simulation of multiphase halogen chemistry involving deliquesced sea-salt aerosols in the marine boundary layer. A common set of aqueous-phase reactions describe chemistry both in the liquid-like (or brine) layer on the grain surface of the snowpack and in "haze" aerosols mainly composed of sulfate in the atmosphere. The process of highly soluble/reactive trace gases, whether entering the snowpack from the atmosphere or formed via gas-phase chemistry in the snowpack interstitial air (SIA), is simulated by the uptake on brine-covered snow grains and subsequent reactions in the aqueous phase while being traveled vertically within the SIA. A "bromine explosion", by which, in a conventional definition, HOBr formed in the ambient air is deposited and then converted heterogeneously to Br2, is a dominant process of reactive bromine formation in the top 1 mm (or less) layer of the snowpack. Deeper in the snowpack, HOBr formed within the SIA leads to an in-snow bromine explosion, but a significant fraction of Br2 is also produced via aqueous radical chemistry in the brine on the surface of the snow grains. These top- and deeper-layer productions of Br2 both contribute to the Br2 release into the atmosphere, but the deeper-layer production is found to be more important for the net outflux of reactive bromine. Although ozone is removed via bromine chemistry, it is also among the key species that control both the conventional and in-snow bromine explosions. On the other hand, aqueous-phase radical chemistry initiated by photolytic OH formation in the liquid-like layer is also a significant contributor to the in-snow source of Br2 and can operate without ozone, whereas the delivery of Br2 to the atmosphere becomes much smaller after ozone is depleted. Catalytic ozone loss via bromine radicals occurs more rapidly in the SIA than in the ambient air, giving rise to apparent dry deposition velocities for ozone from the air to the snow on the order of 10−3 cm s-1 under sunlight. Overall, however, the depletion of ozone in the system is caused predominantly by ozone loss in the ambient air. Increasing depth of the turbulent ABL under windy conditions will delay the build-up of reactive bromine and the resultant loss of ozone, while leading to the higher column amount of BrO in the atmosphere. If moderately saline and acidic snowpack is as prevalent as assumed in our model runs on sea ice during the spring, the shallow, stable ABL under calm weather conditions may undergo persistent ODEs without substantial contributions from blowing/drifting snow and wind-pumping mechanisms, whereas the column densities of BrO in the ABL will likely remain too low during the course of such events to be detected unambiguously by satellite nadir measurements.
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Morin, S., R. Sander y J. Savarino. "Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species". Atmospheric Chemistry and Physics 11, n.º 8 (19 de abril de 2011): 3653–71. http://dx.doi.org/10.5194/acp-11-3653-2011.
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Abstract. The isotope anomaly (Δ17O) of secondary atmospheric species such as nitrate (NO3−) or hydrogen peroxide (H2O2) has potential to provide useful constrains on their formation pathways. Indeed, the Δ17O of their precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ17O in the atmosphere. Interpreting variations of Δ17O in secondary species requires an in-depth understanding of the Δ17O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. This article reviews and illustrates a series of basic concepts relevant to the propagation of the Δ17O of ozone to other reactive or secondary atmospheric species within a photochemical box model. We present results from numerical simulations carried out using the atmospheric chemistry box model CAABA/MECCA to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NOx and HOx. Using a simplified but realistic tropospheric gas-phase chemistry mechanism, Δ17O was propagated from ozone to other species (NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the mass-balance equations, through the implementation of various sets of hypotheses pertaining to the transfer of Δ17O during chemical reactions. The model results confirm that diurnal variations in Δ17O of NOx predicted by the photochemical steady-state relationship during the day match those from the explicit treatment, but not at night. Indeed, the Δ17O of NOx is "frozen" at night as soon as the photolytical lifetime of NOx drops below ca. 10 min. We introduce and quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H2O2, which is of particular relevance to larger-scale simulations of Δ17O where high computational costs cannot be afforded.
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Voigt, C., U. Schumann, T. Jurkat, D. Schäuble, H. Schlager, A. Petzold, J. F. Gayet et al. "In-situ observations of young contrails – overview and selected results from the CONCERT campaign". Atmospheric Chemistry and Physics Discussions 10, n.º 5 (17 de mayo de 2010): 12713–63. http://dx.doi.org/10.5194/acpd-10-12713-2010.
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Abstract. Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. Thereby the Falcon was equipped with a set of instruments to measure particle properties such as the particle size distribution, shape, extinction, chemical composition as well as trace gas concentrations of sulfur dioxide (SO2), reactive nitrogen and halogen species (NO, NOy, HNO3, HONO, HCl), ozone (O3) and carbon monoxide (CO). During 12 mission flights over Western Europe numerous contrails and cirrus clouds were probed at altitudes between 8.5 and 11.6 km and temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. Further we investigate in detail the contrail from a CRJ-2 aircraft detected on 19 November 2008 in 10.1 km altitude. The contrail with an age of 1 to 2 min had average ice crystal concentrations of 128 cm−3 in the size range 0.4
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Liao, J., L. G. Huey, D. J. Tanner, N. Brough, S. Brooks, J. E. Dibb, J. Stutz et al. "Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008". Atmospheric Chemistry and Physics 11, n.º 16 (23 de agosto de 2011): 8577–91. http://dx.doi.org/10.5194/acp-11-8577-2011.
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Abstract. The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring 2007 and summer 2008 to investigate the impact of halogens on HOx (= OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + RO2), ozone (O3), nitrogen oxide (NO), nitric acid (HNO3), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm−3 and 3.0 × 106 molec cm−3 in spring 2007, and 4.2 × 108 molec cm−3 and 4.1 × 106 molec cm−3 in summer 2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly improve the ratio of OH to HO2 + RO2 and the correlation between predictions and observations. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2 + RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.
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Ramsay, Robbie, Chiara F. Di Marco, Matthias Sörgel, Mathew R. Heal, Samara Carbone, Paulo Artaxo, Alessandro C. de Araùjo et al. "Concentrations and biosphere–atmosphere fluxes of inorganic trace gases and associated ionic aerosol counterparts over the Amazon rainforest". Atmospheric Chemistry and Physics 20, n.º 24 (15 de diciembre de 2020): 15551–84. http://dx.doi.org/10.5194/acp-20-15551-2020.
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Abstract. The Amazon rainforest presents a unique, natural laboratory for the study of surface–atmosphere interactions. Its alternation between a near-pristine marine-influenced atmosphere during the wet season and a vulnerable system affected by periodic intrusions of anthropogenic pollution during the dry season provides an opportunity to investigate some fundamental aspects of boundary-layer chemical processes. This study presents the first simultaneous hourly measurements of concentrations, fluxes, and deposition velocities of the inorganic trace gases NH3, HCl, HONO, HNO3, and SO2 as well as their water-soluble aerosol counterparts NH4+, Cl−, NO2-, NO3- and SO42- over the Amazon. Species concentrations were measured in the dry season (from 6 October to 5 November 2017), at the Amazon Tall Tower Observatory (ATTO) in Brazil, using a two-point gradient wet-chemistry instrument (GRadient of AErosols and Gases Online Registration, GRAEGOR) sampling at 42 and 60 m. Fluxes and deposition velocities were derived from the concentration gradients using a modified form of the aerodynamic gradient method corrected for measurement within the roughness sub-layer. Findings from this campaign include observations of elevated concentrations of NH3 and SO2 partially driven by long-range transport (LRT) episodes of pollution and the substantial influence of coarse Cl− and NO3- particulate on overall aerosol mass burdens. From the flux measurements, the dry season budget of total reactive nitrogen dry deposition at the ATTO site was estimated as −2.9 kg N ha-1a-1. HNO3 and HCl were deposited continuously at a rate close to the aerodynamic limit. SO2 was deposited with an average daytime surface resistance (Rc) of 28 s m−1, whilst aerosol components showed average surface deposition velocities of 2.8 and 2.7 mm s−1 for SO42- and NH4+, respectively. Deposition rates of NO3- and Cl− were higher at 7.1 and 7.8 mm s−1, respectively, reflecting their larger average size. The exchange of NH3 and HONO was bidirectional, with NH3 showing emission episodes in the afternoon and HONO in the early morning hours. This work provides a unique dataset to test and improve dry deposition schemes for these compounds for tropical rainforest, which have typically been developed by interpolation from conditions in temperate environments. A future campaign should focus on making similar measurements in the wet season in order to provide a complete view of the annual pattern of inorganic trace gas and coarse aerosol biosphere–atmosphere exchange over tropical rainforest.
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Stockwell, C. E., R. J. Yokelson, S. M. Kreidenweis, A. L. Robinson, P. J. DeMott, R. C. Sullivan, J. Reardon, K. C. Ryan, D. W. T. Griffith y L. Stevens. "Trace gas emissions from combustion of peat, crop residue, domestic biofuels, grasses, and other fuels: configuration and Fourier transform infrared (FTIR) component of the fourth Fire Lab at Missoula Experiment (FLAME-4)". Atmospheric Chemistry and Physics 14, n.º 18 (16 de septiembre de 2014): 9727–54. http://dx.doi.org/10.5194/acp-14-9727-2014.
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Abstract. During the fourth Fire Lab at Missoula Experiment (FLAME-4, October–November 2012) a large variety of regionally and globally significant biomass fuels was burned at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The particle emissions were characterized by an extensive suite of instrumentation that measured aerosol chemistry, size distribution, optical properties, and cloud-nucleating properties. The trace gas measurements included high-resolution mass spectrometry, one- and two-dimensional gas chromatography, and open-path Fourier transform infrared (OP-FTIR) spectroscopy. This paper summarizes the overall experimental design for FLAME-4 – including the fuel properties, the nature of the burn simulations, and the instrumentation employed – and then focuses on the OP-FTIR results. The OP-FTIR was used to measure the initial emissions of 20 trace gases: CO2, CO, CH4, C2H2, C2H4, C3H6, HCHO, HCOOH, CH3OH, CH3COOH, glycolaldehyde, furan, H2O, NO, NO2, HONO, NH3, HCN, HCl, and SO2. These species include most of the major trace gases emitted by biomass burning, and for several of these compounds, this is the first time their emissions are reported for important fuel types. The main fire types included African grasses, Asian rice straw, cooking fires (open (three-stone), rocket, and gasifier stoves), Indonesian and extratropical peat, temperate and boreal coniferous canopy fuels, US crop residue, shredded tires, and trash. Comparisons of the OP-FTIR emission factors (EFs) and emission ratios (ERs) to field measurements of biomass burning verify that the large body of FLAME-4 results can be used to enhance the understanding of global biomass burning and its representation in atmospheric chemistry models. Crop residue fires are widespread globally and account for the most burned area in the US, but their emissions were previously poorly characterized. Extensive results are presented for burning rice and wheat straw: two major global crop residues. Burning alfalfa produced the highest average NH3 EF observed in the study (6.63 ± 2.47 g kg−1), while sugar cane fires produced the highest EF for glycolaldehyde (6.92 g kg−1) and other reactive oxygenated organic gases such as HCHO, HCOOH, and CH3COOH. Due to the high sulfur and nitrogen content of tires, they produced the highest average SO2 emissions (26.2 ± 2.2 g kg−1) and high NOx and HONO emissions. High variability was observed for peat fire emissions, but they were consistently characterized by large EFs for NH3 (1.82 ± 0.60 g kg−1) and CH4 (10.8 ± 5.6 g kg−1). The variability observed in peat fire emissions, the fact that only one peat fire had previously been subject to detailed emissions characterization, and the abundant emissions from tropical peatlands all impart high value to our detailed measurements of the emissions from burning three Indonesian peat samples. This study also provides the first EFs for HONO and NO2 for Indonesian peat fires. Open cooking fire emissions of HONO and HCN are reported for the first time, and the first emissions data for HCN, NO, NO2, HONO, glycolaldehyde, furan, and SO2 are reported for "rocket" stoves: a common type of improved cookstove. The HCN / CO emission ratios for cooking fires (1.72 × 10−3 ± 4.08 × 10−4) and peat fires (1.45 × 10−2 ± 5.47 × 10−3) are well below and above the typical values for other types of biomass burning, respectively. This would affect the use of HCN / CO observations for source apportionment in some regions. Biomass burning EFs for HCl are rare and are reported for the first time for burning African savanna grasses. High emissions of HCl were also produced by burning many crop residues and two grasses from coastal ecosystems. HCl could be the main chlorine-containing gas in very fresh smoke, but rapid partitioning to aerosol followed by slower outgassing probably occurs.
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Marx, O., C. Brümmer, C. Ammann, V. Wolff y A. Freibauer. "TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen". Atmospheric Measurement Techniques Discussions 4, n.º 6 (19 de diciembre de 2011): 7623–55. http://dx.doi.org/10.5194/amtd-4-7623-2011.
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Abstract. The input and loss of plant available nitrogen (N) from/to the atmosphere can be an important factor for the productivity of ecosystems and thus for its carbon and greenhouse gas exchange. We present a novel converter for the measurement of total reactive nitrogen (TRANC: Total Reactive Atmospheric Nitrogen Converter), which offers the opportunity to quantify the sum of all airborne reactive nitrogen (Nr) compounds in high time resolution. The basic concept of the TRANC is the full conversion of total Nr to nitrogen monoxide (NO) within two reaction steps. Initially, reduced N compounds are being oxidised, and oxidised N compounds are thermally converted to lower oxidation states. Particulate N is being sublimated and oxidised or reduced afterwards. In a second step, remaining higher N oxides or those originated in the first step are catalytically converted to NO with carbon monoxide used as reduction gas. The converter is combined with a fast response chemiluminescence detector (CLD) for NO analysis and its performance was tested for the most relevant gaseous and particulate Nr species under both laboratory and field conditions. Recovery rates during laboratory tests for NH3 and NO2 were found to be 95 and 99%, respectively, and 97% when the two gases were combined. In-field longterm stability over an 11-month period was approved by a value of 91% for NO2. Effective conversion was also found for ammonium and nitrate containing particles. The recovery rate of total ambient Nr was tested against the sum of individual measurements of NH3, HNO3, HONO, NH4+, NO3−, and NOx using a combination of different well-established devices. The results show that the TRANC-CLD system precisely captures fluctuations in Nr concentrations and also matches the sum of all Nr compounds measured by the different single techniques. The TRANC features a specific design with very short distance between the sample air inlet and the place where the thermal and catalytic conversions to NO occur. This assures a short residence time of the sample air inside the instrument, and minimises wall sorption problems of water soluble compounds. The fast response time (half-value periods of 0.30 s were found during concentration step changes) and high accuracy in capturing the dominant Nr species enables the converter to be used in an eddy covariance setup. Although a source attribution of specific Nr compounds is not possible, the TRANC is a new reliable tool for permanent measurements of the net Nr flux between ecosystem and atmosphere at a relatively low maintenance and reasonable cost level allowing for diurnal, seasonal and annual investigations.
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Marx, O., C. Brümmer, C. Ammann, V. Wolff y A. Freibauer. "TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen". Atmospheric Measurement Techniques 5, n.º 5 (11 de mayo de 2012): 1045–57. http://dx.doi.org/10.5194/amt-5-1045-2012.
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Abstract. The input and loss of plant available nitrogen (reactive nitrogen: Nr) from/to the atmosphere can be an important factor for the productivity of ecosystems and thus for its carbon and greenhouse gas exchange. We present a novel converter for reactive nitrogen (TRANC: Total Reactive Atmospheric Nitrogen Converter), which offers the opportunity to quantify the sum of all airborne reactive nitrogen compounds (∑Nr) in high time resolution. The basic concept of the TRANC is the full conversion of all Nr to nitrogen monoxide (NO) within two reaction steps. Initially, reduced Nr compounds are being oxidised, and oxidised Nr compounds are thermally converted to lower oxidation states. Particulate Nr is being sublimated and oxidised or reduced afterwards. In a second step, remaining higher nitrogen oxides or those generated in the first step are catalytically converted to NO with carbon monoxide used as reduction gas. The converter is combined with a fast response chemiluminescence detector (CLD) for NO analysis and its performance was tested for the most relevant gaseous and particulate Nr species under both laboratory and field conditions. Recovery rates during laboratory tests for NH3 and NO2 were found to be 95 and 99%, respectively, and 97% when the two gases were combined. In-field longterm stability over an 11-month period was approved by a value of 91% for NO2. Effective conversion was also found for ammonium and nitrate containing particles. The recovery rate of total ambient Nr was tested against the sum of individual measurements of NH3, HNO3, HONO, NH4+, NO3−, and NOx using a combination of different well-established devices. The results show that the TRANC-CLD system precisely captures fluctuations in ∑Nr concentrations and also matches the sum of all individual Nr compounds measured by the different single techniques. The TRANC features a specific design with very short distance between the sample air inlet and the place where the thermal and catalytic conversions to NO occur. This assures a short residence time of the sample air inside the instrument, and minimises wall sorption problems of water soluble compounds. The fast response time (e-folding times of 0.30 to 0.35 s were found during concentration step changes) and high accuracy in capturing the dominant Nr species enables the converter to be used in an eddy covariance setup. Although a source attribution of specific Nr compounds is not possible, the TRANC is a new reliable tool for permanent measurements of the net ∑Nr flux between ecosystem and atmosphere at a relatively low maintenance and reasonable cost level allowing for diurnal, seasonal and annual investigations.
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Liao, J., L. G. Huey, E. Scheuer, J. E. Dibb, R. E. Stickel, D. J. Tanner, J. A. Neuman et al. "Characterization of soluble bromide measurements and a case study of BrO observations during ARCTAS". Atmospheric Chemistry and Physics 12, n.º 3 (2 de febrero de 2012): 1327–38. http://dx.doi.org/10.5194/acp-12-1327-2012.
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Abstract. A focus of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission was examination of bromine photochemistry in the spring time high latitude troposphere based on aircraft and satellite measurements of bromine oxide (BrO) and related species. The NASA DC-8 aircraft utilized a chemical ionization mass spectrometer (CIMS) to measure BrO and a mist chamber (MC) to measure soluble bromide. We have determined that the MC detection efficiency to molecular bromine (Br2), hypobromous acid (HOBr), bromine oxide (BrO), and hydrogen bromide (HBr) as soluble bromide (Br−) was 0.9±0.1, 1.06+0.30/−0.35, 0.4±0.1, and 0.95±0.1, respectively. These efficiency factors were used to estimate soluble bromide levels along the DC-8 flight track of 17 April 2008 from photochemical calculations constrained to in situ BrO measured by CIMS. During this flight, the highest levels of soluble bromide and BrO were observed and atmospheric conditions were ideal for the space-borne observation of BrO. The good agreement (R2 = 0.76; slope = 0.95; intercept = −3.4 pmol mol−1) between modeled and observed soluble bromide, when BrO was above detection limit (>2 pmol mol−1) under unpolluted conditions (NO<10 pmol mol−1), indicates that the CIMS BrO measurements were consistent with the MC soluble bromide and that a well characterized MC can be used to derive mixing ratios of some reactive bromine compounds. Tropospheric BrO vertical column densities (BrOVCD) derived from CIMS BrO observations compare well with BrOTROPVCD from OMI on 17 April 2008.
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Ma, Tianyi, Kunlun Huang y Nan Cheng. "Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control". International Journal of Molecular Sciences 24, n.º 17 (28 de agosto de 2023): 13342. http://dx.doi.org/10.3390/ijms241713342.
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Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.
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Toyota, K., J. C. McConnell, A. Lupu, L. Neary, C. A. McLinden, A. Richter, R. Kwok et al. "Synoptic-scale meteorological control on reactive bromine production and ozone depletion in the Arctic boundary layer: 3-D simulation with the GEM-AQ model". Atmospheric Chemistry and Physics Discussions 10, n.º 11 (5 de noviembre de 2010): 26207–78. http://dx.doi.org/10.5194/acpd-10-26207-2010.
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Abstract. Episodes of high bromine levels and surface ozone depletion in the springtime Arctic are simulated by an online air-quality model, GEM-AQ, with gas-phase and heterogeneous reactions of inorganic bromine species and a simple scheme of air-snowpack chemical interactions implemented for this study. Snowpack on sea ice is assumed to be the only source of bromine to the atmosphere and capable of converting relatively stable bromine species to photolabile Br2 via air-snowpack interactions. A "bromine explosion", by which Br− retained in the snowpack is autocatalytically released to the atmosphere as a result of dry deposition of HOBr and BrONO2, is assumed to occur on young, first-year (FY) sea ice (or its overlying snowpack), whereas the snowpack on old, multi-year (MY) sea ice and over land is assumed only to recycle a part (but up to 100%) of bromine reservoirs lost via dry deposition back to Br2. Model runs are performed for April 2001 at a horizontal resolution of approximately 100 km × 100 km in the Arctic. The model simulates temporal variations in surface ozone mixing ratios as observed at stations in the high Arctic and the synoptic-scale evolution of enhanced BrO column amounts ("BrO clouds") as seen from satellite reasonably well. The results strongly suggest: (1) a ubiquitous source of reactive bromine exists on the FY sea ice during the Arctic springtime; and (2) the timing of bromine release to the atmosphere is largely controlled by meteorological forcing on the transport of ozone to the near-surface air. Also, if the surface snowpack supplies most of the reactive bromine in the Arctic boundary layer, it should be capable of releasing reactive bromine at temperatures as high as −10 °C, particularly on the FY sea ice in the central and eastern Arctic Ocean. Dynamically-induced BrO column variability in the lowermost stratosphere appears to interfere with the use of satellite BrO column measurements for interpreting BrO variability in the lower troposphere but probably not to the extent of totally obscuring "BrO clouds" associated with the surface source of bromine in the high Arctic. Contrary to our original intention, the present air-snowpack interaction scheme yields a majority of atmospheric bromine input via Br2 release associated empirically with a dry deposition of ozone on the snow/ice surface under sunlight to represent a trigger of bromine explosion. This implies that the bromine explosion actually occurs in the interstitial air of snowpack and/or is accelerated by heterogeneous reactions on the surface of wind-blown snow in ambient air, both of which are missing in our model but could have been approximated by a parameter adjustment for the yield of Br2 from the trigger.
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Mushinski, Ryan M., Richard P. Phillips, Zachary C. Payne, Rebecca B. Abney, Insu Jo, Songlin Fei, Sally E. Pusede, Jeffrey R. White, Douglas B. Rusch y Jonathan D. Raff. "Microbial mechanisms and ecosystem flux estimation for aerobic NOyemissions from deciduous forest soils". Proceedings of the National Academy of Sciences 116, n.º 6 (18 de enero de 2019): 2138–45. http://dx.doi.org/10.1073/pnas.1814632116.
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Reactive nitrogen oxides (NOy; NOy= NO + NO2+ HONO) decrease air quality and impact radiative forcing, yet the factors responsible for their emission from nonpoint sources (i.e., soils) remain poorly understood. We investigated the factors that control the production of aerobic NOyin forest soils using molecular techniques, process-based assays, and inhibitor experiments. We subsequently used these data to identify hotspots for gas emissions across forests of the eastern United States. Here, we show that nitrogen oxide soil emissions are mediated by microbial community structure (e.g., ammonium oxidizer abundances), soil chemical characteristics (pH and C:N), and nitrogen (N) transformation rates (net nitrification). We find that, while nitrification rates are controlled primarily by chemoautotrophic ammonia-oxidizing archaea (AOA), the production of NOyis mediated in large part by chemoautotrophic ammonia-oxidizing bacteria (AOB). Variation in nitrification rates and nitrogen oxide emissions tracked variation in forest communities, as stands dominated by arbuscular mycorrhizal (AM) trees had greater N transformation rates and NOyfluxes than stands dominated by ectomycorrhizal (ECM) trees. Given mapped distributions of AM and ECM trees from 78,000 forest inventory plots, we estimate that broadleaf forests of the Midwest and the eastern United States as well as the Mississippi River corridor may be considered hotspots of biogenic NOyemissions. Together, our results greatly improve our understanding of NOyfluxes from forests, which should lead to improved predictions about the atmospheric consequences of tree species shifts owing to land management and climate change.
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Wang, Weihong, Michael J. Ezell, Pascale S. J. Lakey, Kifle Z. Aregahegn, Manabu Shiraiwa y Barbara J. Finlayson-Pitts. "Unexpected formation of oxygen-free products and nitrous acid from the ozonolysis of the neonicotinoid nitenpyram". Proceedings of the National Academy of Sciences 117, n.º 21 (11 de mayo de 2020): 11321–27. http://dx.doi.org/10.1073/pnas.2002397117.
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The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R1N)(R2N)C=CHNO2] pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant, such compounds may be oxidized on contact with air to form new products that have different toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of NPM by gas-phase ozone produces unexpected products, the majority of which do not contain oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations, occurred throughout the film. The rate constant derived for the O3−NPM reaction is 1 × 10−18cm3⋅s−1, and the diffusion coefficient of ozone in the thin film is 9 × 10−10cm2⋅s−1. These findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that known chemical mechanisms for individual moieties in such compounds cannot be extrapolated from simple alkenes. This is critical for guiding assessments of the environmental fates and impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future alternatives.
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Custard, K. D., C. R. Thompson, K. A. Pratt, P. B. Shepson, J. Liao, L. G. Huey, J. J. Orlando et al. "The NO<sub>x</sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer". Atmospheric Chemistry and Physics Discussions 15, n.º 6 (19 de marzo de 2015): 8329–60. http://dx.doi.org/10.5194/acpd-15-8329-2015.
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Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean–Atmosphere–Sea Ice–Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase radical chemistry, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr, with a concomitant, decreased net O3 loss rate. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.
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Custard, K. D., C. R. Thompson, K. A. Pratt, P. B. Shepson, J. Liao, L. G. Huey, J. J. Orlando et al. "The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer". Atmospheric Chemistry and Physics 15, n.º 18 (29 de septiembre de 2015): 10799–809. http://dx.doi.org/10.5194/acp-15-10799-2015.
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Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean – Atmosphere – Sea Ice – Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.
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Badia, Alba, Claire E. Reeves, Alex R. Baker, Alfonso Saiz-Lopez, Rainer Volkamer, Theodore K. Koenig, Eric C. Apel et al. "Importance of reactive halogens in the tropical marine atmosphere: a regional modelling study using WRF-Chem". Atmospheric Chemistry and Physics 19, n.º 5 (12 de marzo de 2019): 3161–89. http://dx.doi.org/10.5194/acp-19-3161-2019.
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Abstract. This study investigates the impact of reactive halogen species (RHS, containing chlorine (Cl), bromine (Br) or iodine (I)) on atmospheric chemistry in the tropical troposphere and explores the sensitivity to uncertainties in the fluxes of RHS to the atmosphere and their chemical processing. To do this, the regional chemistry transport model WRF-Chem has been extended to include Br and I, as well as Cl chemistry for the first time, including heterogeneous recycling reactions involving sea-salt aerosol and other particles, reactions of Br and Cl with volatile organic compounds (VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic iodine. The study focuses on the tropical east Pacific using field observations from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) campaign (January–February 2012) to evaluate the model performance. Including all the new processes, the model does a reasonable job reproducing the observed mixing ratios of bromine oxide (BrO) and iodine oxide (IO), albeit with some discrepancies, some of which can be attributed to difficulties in the model's ability to reproduce the observed halocarbons. This is somewhat expected given the large uncertainties in the air–sea fluxes of the halocarbons in a region where there are few observations of their seawater concentrations. We see a considerable impact on the inorganic bromine (Bry) partitioning when heterogeneous chemistry is included, with a greater proportion of the Bry in active forms such as BrO, HOBr and dihalogens. Including debromination of sea salt increases BrO slightly throughout the free troposphere, but in the tropical marine boundary layer, where the sea-salt particles are plentiful and relatively acidic, debromination leads to overestimation of the observed BrO. However, it should be noted that the modelled BrO was extremely sensitive to the inclusion of reactions between Br and the oxygenated VOCs (OVOCs), which convert Br to HBr, a far less reactive form of Bry. Excluding these reactions leads to modelled BrO mixing ratios greater than observed. The reactions between Br and aldehydes were found to be particularly important, despite the model underestimating the amount of aldehydes observed in the atmosphere. There are only small changes to the inorganic iodine (Iy) partitioning and IO when the heterogeneous reactions, primarily on sea salt, are included. Our model results show that tropospheric Ox loss due to halogens ranges between 25 % and 60 %. Uncertainties in the heterogeneous chemistry accounted for a small proportion of this range (25 % to 31 %). This range is in good agreement with other estimates from state-of-the-art atmospheric chemistry models. The upper bound is found when reactions between Br and Cl with VOCs are not included and, consequently, Ox loss by BrOx, ClOx and IOx cycles is high (60 %). With the inclusion of halogens in the troposphere, O3 is reduced by 7 ppbv on average. However, when reactions between Br and Cl with VOCs are not included, O3 is much lower than observed. Therefore, the tropospheric Ox budget is highly sensitive to the inclusion of halogen reactions with VOCs and to the uncertainties in current understanding of these reactions and the abundance of VOCs in the remote marine atmosphere.
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El Zein, A. y Y. Bedjanian. "Interaction of NO<sub>2</sub> with TiO<sub>2</sub> surface under UV irradiation: measurements of the uptake coefficient". Atmospheric Chemistry and Physics Discussions 11, n.º 10 (12 de octubre de 2011): 27861–85. http://dx.doi.org/10.5194/acpd-11-27861-2011.
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Abstract. The interaction of NO2 with TiO2 solid films was studied under UV irradiation using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The NO2 to TiO2 reactive uptake coefficient was measured from the kinetics of NO2 loss on TiO2 coated Pyrex rods as a function of NO2 concentration, irradiance intensity (JNO2 = 0.002–0.012 s−1), relative humidity (RH = 0.06–69%), temperature (T = 275–320 K) and partial pressure of oxygen (0.001–3 Torr). TiO2 surface deactivation upon exposure to NO2 was observed. The initial uptake coefficient of NO2 on illuminated TiO2 surface (with 90 ppb of NO2 and JNO2 ≅ 0.006 s−1) was found to be γ0 = (1.2 &pm; 0.4) × 10−4 (calculated using BET surface area) under dry conditions at T = 300 K. The steady state uptake, γ, was several tens of times lower than the initial one, independent of relative humidity, and was found to decrease in the presence of molecular oxygen. In addition, it was shown that γ is not linearly dependent on the photon flux and seems to level off under atmospheric conditions. Finally, the following expression for γ was derived, γ = 2.3 × 10−3 exp(−1910/T)/(1 + P0.36) (where P is O2 pressure in Torr), and recommended for atmospheric applications (for any RH, near 90 ppb of NO2 and JNO2 = 0.006 s−1). In addition, HONO, NO and N2O were found to be released into the gas phase as a result of the heterogeneous photoreaction of NO2 with TiO2 surface. Detailed study of the yield of these products is the subject of our current work.
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Wang, Xuan, Daniel J. Jacob, Sebastian D. Eastham, Melissa P. Sulprizio, Lei Zhu, Qianjie Chen, Becky Alexander et al. "The role of chlorine in global tropospheric chemistry". Atmospheric Chemistry and Physics 19, n.º 6 (29 de marzo de 2019): 3981–4003. http://dx.doi.org/10.5194/acp-19-3981-2019.
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Abstract. We present a comprehensive simulation of tropospheric chlorine within the GEOS-Chem global 3-D model of oxidant–aerosol–halogen atmospheric chemistry. The simulation includes explicit accounting of chloride mobilization from sea salt aerosol by acid displacement of HCl and by other heterogeneous processes. Additional small sources of tropospheric chlorine (combustion, organochlorines, transport from stratosphere) are also included. Reactive gas-phase chlorine Cl*, including Cl, ClO, Cl2, BrCl, ICl, HOCl, ClNO3, ClNO2, and minor species, is produced by the HCl+OH reaction and by heterogeneous conversion of sea salt aerosol chloride to BrCl, ClNO2, Cl2, and ICl. The model successfully simulates the observed mixing ratios of HCl in marine air (highest at northern midlatitudes) and the associated HNO3 decrease from acid displacement. It captures the high ClNO2 mixing ratios observed in continental surface air at night and attributes the chlorine to HCl volatilized from sea salt aerosol and transported inland following uptake by fine aerosol. The model successfully simulates the vertical profiles of HCl measured from aircraft, where enhancements in the continental boundary layer can again be largely explained by transport inland of the marine source. It does not reproduce the boundary layer Cl2 mixing ratios measured in the WINTER aircraft campaign (1–5 ppt in the daytime, low at night); the model is too high at night, which could be due to uncertainty in the rate of the ClNO2+Cl- reaction, but we have no explanation for the high observed Cl2 in daytime. The global mean tropospheric concentration of Cl atoms in the model is 620 cm−3 and contributes 1.0 % of the global oxidation of methane, 20 % of ethane, 14 % of propane, and 4 % of methanol. Chlorine chemistry increases global mean tropospheric BrO by 85 %, mainly through the HOBr+Cl- reaction, and decreases global burdens of tropospheric ozone by 7 % and OH by 3 % through the associated bromine radical chemistry. ClNO2 chemistry drives increases in ozone of up to 8 ppb over polluted continents in winter.
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Ge, Yao, Massimo Vieno, David S. Stevenson, Peter Wind y Mathew R. Heal. "A new assessment of global and regional budgets, fluxes, and lifetimes of atmospheric reactive N and S gases and aerosols". Atmospheric Chemistry and Physics 22, n.º 12 (28 de junio de 2022): 8343–68. http://dx.doi.org/10.5194/acp-22-8343-2022.
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Abstract. We used the EMEP MSC-W (European Monitoring and Evaluation Programme Meteorological Synthesizing Centre – West) model version 4.34 coupled with WRF (Weather Research and Forecasting) model version 4.2.2 meteorology to undertake a present-day (2015) global and regional quantification of the concentrations, deposition, budgets, and lifetimes of atmospheric reactive N (Nr) and S (Sr) species. These are quantities that cannot be derived from measurements alone. In areas with high levels of reduced Nr (RDN = NH3+ NH4+), oxidized Nr (OXN = NOx+ HNO3+ HONO + N2O5 + NO3-+ “Other OXN” species), and oxidized Sr (OXS = SO2+ SO42-), RDN is predominantly in the form of NH3 (NH4+ typically <20 %), OXN has majority gaseous species composition, and OXS predominantly comprises SO42- except near major SO2 sources. Most continental regions are now “ammonia rich”, more so than previously, which indicates that, although reducing NH3 emissions will decrease the RDN concentration, decreasing these emissions will have little effect on mitigating secondary inorganic aerosol (SIA). South Asia is the most ammonia-rich region. Coastal areas around East Asia, northern Europe, and the north-eastern United States are “nitrate rich” where NH4NO3 formation is limited by NH3. These locations experience transport of OXN from the adjacent continent and/or direct shipping emissions of NOx, but NH3 concentrations are lower. The least populated continental areas and most marine areas are “sulfate rich”. Deposition of OXN (57.9 TgN yr−1, 51 %) and RDN (55.5 TgN yr−1, 49 %) contribute almost equally to total nitrogen deposition. OXS deposition is 50.5 TgS yr−1. Globally, wet and dry deposition contribute similarly to RDN deposition; for OXN and OXS, wet deposition contributes slightly more. Dry deposition of NH3 is the largest contributor to RDN deposition in most regions except for the Rest of Asia area and marine sectors where NH3 emissions are small and RDN deposition is mainly determined by the transport and rainout of NH4+ (rather than rainout of gaseous NH3). Thus, reductions in NH3 would efficiently reduce the deposition of RDN in most continental regions. The two largest contributors to OXN deposition in all regions are HNO3 and coarse NO3- (via both wet and dry deposition). The deposition of fine NO3- is only important over East Asia. The tropospheric burden of RDN is 0.75 TgN, of which NH3 and NH4+ comprise 32 % (0.24 TgN; lifetime of 1.6 d) and 68 % (0.51 TgN; lifetime of 8.9 d) respectively. The lifetime of RDN (4.9–5.2 d) is shorter than that of OXN (7.6–7.7 d), which is consistent with a total OXN burden (1.20 TgN) almost double that of RDN. The tropospheric burden of OXS is 0.78 TgS with a lifetime of 5.6–5.9 d. Total nitrate burden is 0.58 TgN with fine NO3- only constituting 10 % of this total, although fine NO3- dominates in eastern China, Europe, and eastern North America. It is important to account for contributions of coarse nitrate to global nitrate budgets. Lifetimes of RDN, OXN, and OXS species vary by a factor of 4 across different continental regions. In East Asia, lifetimes for RDN (2.9–3.0 d), OXN (3.9–4.5 d), and OXS (3.4–3.7 d) are short, whereas lifetimes in the Rest of Asia and Africa regions are about twice as long. South Asia is the largest net exporter of RDN (2.21 TgN yr−1, 29 % of its annual emission), followed by the Euro_Medi region. Despite having the largest RDN emissions and deposition, East Asia has only small net export and is therefore largely responsible for its own RDN pollution. Africa is the largest net exporter of OXN (1.92 TgN yr−1, 22 %), followed by Euro_Medi (1.61 TgN yr−1, 26 %). Considerable marine anthropogenic Nr and Sr pollution is revealed by the large net import of RDN, OXN, and OXS to these areas. Our work demonstrates the substantial regional variation in Nr and Sr budgets and the need for modelling to simulate the chemical and meteorological linkages underpinning atmospheric responses to precursor emissions.
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Yokelson, R. J., T. Karl, P. Artaxo, D. R. Blake, T. J. Christian, D. W. T. Griffith, A. Guenther y W. M. Hao. "The Tropical Forest and fire emissions experiment: overview and airborne fire emission factor measurements". Atmospheric Chemistry and Physics Discussions 7, n.º 3 (23 de mayo de 2007): 6903–58. http://dx.doi.org/10.5194/acpd-7-6903-2007.
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Abstract. The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by uv absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on September 8. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3-4-fold increase in aerosol loading in the São Paulo area for several days.
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Yokelson, R. J., T. Karl, P. Artaxo, D. R. Blake, T. J. Christian, D. W. T. Griffith, A. Guenther y W. M. Hao. "The Tropical Forest and Fire Emissions Experiment: overview and airborne fire emission factor measurements". Atmospheric Chemistry and Physics 7, n.º 19 (9 de octubre de 2007): 5175–96. http://dx.doi.org/10.5194/acp-7-5175-2007.
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Abstract. The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by UV absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on 8 September. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3–4-fold increase in aerosol loading in the São Paulo area for several days.
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Twigg, M. M., C. F. Di Marco, S. Leeson, N. van Dijk, M. R. Jones, I. D. Leith, E. Morrison et al. "Water soluble aerosols and gases at a UK background site – Part 1: Controls of PM<sub>2.5</sub> and PM<sub>10</sub> aerosol composition". Atmospheric Chemistry and Physics 15, n.º 14 (23 de julio de 2015): 8131–45. http://dx.doi.org/10.5194/acp-15-8131-2015.
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Abstract. There is limited availability of long-term, high temporal resolution, chemically speciated aerosol measurements which can provide further insight into the health and environmental impacts of particulate matter. The Monitor for AeRosols and Gases (MARGA, Applikon B.V., NL) allows for the characterisation of the inorganic components of PM10 and PM2.5 (NH4+, NO3-, SO42-, Cl-, Na+, K+, Ca2+, Mg2+) and inorganic reactive gases (NH3, SO2, HCl, HONO and HNO3) at hourly resolution. The following study presents 6.5 years (June 2006 to December 2012) of quasi-continuous observations of PM2.5 and PM10 using the MARGA at the UK EMEP supersite, Auchencorth Moss, SE Scotland. Auchencorth Moss was found to be representative of a remote European site with average total water soluble inorganic mass of PM2.5 of 3.82 μg m−3. Anthropogenically derived secondary inorganic aerosols (sum of NH4+, NO3- and nss-SO42−) were the dominating species (63 %) of PM2.5. In terms of equivalent concentrations, NH4+ provided the single largest contribution to PM2.5 fraction in all seasons. Sea salt was the main component (73 %) of the PMcoarse fraction (PM10-PM2.5), though NO3- was also found to make a relatively large contribution to the measured mass (17 %) providing evidence of considerable processing of sea salt in the coarse mode. There was on occasions evidence of aerosol from combustion events being transported to the site in 2012 as high K+ concentrations (deviating from the known ratio in sea salt) coincided with increases in black carbon at the site. Pollution events in PM10 (defined as concentrations > 12 μg m−3) were on average dominated by NH4+ and NO3-, where smaller loadings at the site tended to be dominated by sea salt. As with other western European sites, the charge balance of the inorganic components resolved were biased towards cations, suggesting the aerosol was basic or more likely that organic acids contributed to the charge balance. This study demonstrates the UK background atmospheric composition is primarily driven by meteorology with sea salt dominating air masses from the Atlantic Ocean and the Arctic, whereas secondary inorganic aerosols tended to dominate air masses from continental Europe.