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1
Röckmann, T., S. Walter, B. Bohn, R. Wegener, H. Spahn, T. Brauers, R. Tillmann, E. Schlosser, R. Koppmann e F. Rohrer. "Isotope effect in the formation of H<sub>2</sub> from H<sub>2</sub>CO studied at the atmospheric simulation chamber SAPHIR". Atmospheric Chemistry and Physics 10, n.º 12 (16 de junho de 2010): 5343–57. http://dx.doi.org/10.5194/acp-10-5343-2010.
Resumo:
Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in the SAPHIR atmosphere simulation chamber under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only an indirect effect and cannot be effectively constrained. The molecular channel kinetic isotope effect KIEmol, the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) at surface pressure, is determined to be KIEmol=1.63−0.046+0.038. This is similar to the kinetic isotope effect for the total removal of HCHO from a recent relative rate experiment (KIEtot=1.58±0.03), which indicates that the KIEs in the molecular and radical photolysis channels at surface pressure (≈100 kPa) may not be as different as described previously in the literature.
2
Epstein, S. A., e S. A. Nizkorodov. "A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase". Atmospheric Chemistry and Physics Discussions 12, n.º 4 (19 de abril de 2012): 10015–58. http://dx.doi.org/10.5194/acpd-12-10015-2012.
Resumo:
Abstract. Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. We find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.
3
Cataldo, Franco, Giovanni Strazzulla e Susana Iglesias-Groth. "UV photolysis of polyynes at λ=254 nm and at λ>222 nm". International Journal of Astrobiology 7, n.º 2 (abril de 2008): 107–16. http://dx.doi.org/10.1017/s147355040800414x.
Resumo:
AbstractFor the first time the kinetic rate constants of the UV photolysis of polyynes C6H2, C8H2, C10H2, C12H2 and C14H2 under rigorously inert atmosphere have been determined in three different solvents: n-hexane, n-heptane and decalin. First- or pseudofirst-order kinetics appear suitable to describe the photolysis of these molecules and k values in the range between 3.0×10−3 s−1 and 4.6×10−3 s−1 have been determined. The unique exception is represented by C6H2 which photolyses more slowly with k=3.2×10−4 s−1. Two different UV sources have been used in the present study: a low-pressure mercury lamp having a monochromatic emission at 253.7 nm and a medium-to high-pressure lamp with a continuous emission between 222 nm and 580 nm. The results are of interest in the understanding, and also the modelling, of the fate of polyynes released by carbon-rich stars in the interstellar medium or the polyynes released by comets in their active phase.
4
Epstein, S. A., e S. A. Nizkorodov. "A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase". Atmospheric Chemistry and Physics 12, n.º 17 (12 de setembro de 2012): 8205–22. http://dx.doi.org/10.5194/acp-12-8205-2012.
Resumo:
Abstract. Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. For example, we find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.
5
Gálvez, Óscar, M. Teresa Baeza-Romero, Mikel Sanz e Alfonso Saiz-Lopez. "Photolysis of frozen iodate salts as a source of active iodine in the polar environment". Atmospheric Chemistry and Physics 16, n.º 19 (12 de outubro de 2016): 12703–13. http://dx.doi.org/10.5194/acp-16-12703-2016.
Resumo:
Abstract. Reactive halogens play a key role in the oxidation capacity of the polar troposphere. However, sources and mechanisms, particularly those involving active iodine, are still poorly understood. In this paper, the photolysis of an atmospherically relevant frozen iodate salt has been experimentally studied using infrared (IR) spectroscopy. The samples were generated at low temperatures in the presence of different amounts of water. The IR spectra have confirmed that, under near-ultraviolet–visible (UV–Vis) radiation, iodate is efficiently photolysed. The integrated IR absorption coefficient of the iodate anion on the band at 750 cm−1 has been measured to be A = 9.8 ± 0.5 × 10−17 cm molecule−1. The photolysis rate of the ammonium iodate salt was measured by monitoring the decay of ammonium or iodate IR bands (1430 and 750 cm−1 respectively) in the presence of a solar simulator. The absorption cross section of the liquid solutions of ammonium iodate at wavelengths relevant for the troposphere (250 to 400 nm) has been obtained and used to estimate the photolytic quantum yield for the frozen salt. Finally, using an atmospheric model, constrained with the experimental data, we suggest that the photolysis of iodate in frozen salt can potentially provide a pathway for the release of active iodine to the polar atmosphere.
6
Watanabe, Yasuto, e Kazumi Ozaki. "Relative Abundances of CO2, CO, and CH4 in Atmospheres of Earth-like Lifeless Planets". Astrophysical Journal 961, n.º 1 (1 de janeiro de 2024): 1. http://dx.doi.org/10.3847/1538-4357/ad10a2.
Resumo:
Abstract Carbon is an essential element for life on Earth, and the relative abundances of major carbon species (CO2, CO, and CH4) in the atmosphere exert fundamental controls on planetary climate and biogeochemistry. Here we employed a theoretical model of atmospheric chemistry to investigate diversity in the atmospheric abundances of CO2, CO, and CH4 on Earth-like lifeless planets orbiting Sun-like (F-, G-, and K-type) stars. We focused on the conditions for the formation of a CO-rich atmosphere, which would be favorable for the origin of life. Results demonstrated that elevated atmospheric CO2 levels trigger photochemical instability of the CO budget in the atmosphere (i.e., CO runaway) owing to enhanced CO2 photolysis relative to H2O photolysis. Higher volcanic outgassing fluxes of reduced C (CO and CH4) also tend to initiate CO runaway. Our systematic examinations revealed that anoxic atmospheres of Earth-like lifeless planets could be classified in the phase space of CH4/CO2 versus CO/CO2, where a distinct gap in atmospheric carbon chemistry is expected to be observed. Our findings indicate that the gap structure is a general feature of Earth-like lifeless planets with reducing atmospheres orbiting Sun-like (F-, G-, and K-type) stars.
7
Gálvez, O., M. T. Baeza-Romero, M. Sanz e A. Saiz-Lopez. "Photolysis of frozen iodate salts as a source of active iodine in the polar environment". Atmospheric Chemistry and Physics Discussions 15, n.º 19 (15 de outubro de 2015): 27917–42. http://dx.doi.org/10.5194/acpd-15-27917-2015.
Resumo:
Abstract. Reactive halogens play a key role in the oxidation capacity of the polar troposphere. However, sources and mechanisms, particularly those involving active iodine, are still poorly understood. In this paper, the photolysis of an atmospherically relevant frozen iodate salt has been experimentally studied using infrared (IR) spectroscopy. The samples were generated at low temperatures in the presence of different amounts of water. The IR spectra have confirmed that under near-UV/Vis radiation iodate is efficiently photolyzed. The integrated IR absorption coefficient of the iodate anion on the band at 750 cm−1 has been measured to be A = 9.5 × 10−17 cm molec−1. Using this value, a lower limit of the integrated absorption cross section of iodate, in an ammonium frozen salt, has been estimated for the first time at wavelengths relevant for tropospheric studies (σ = 1.1 × 10−20 cm2 nm molec−1 from 300 to 900 nm). According to this, we suggest that the photolysis of iodate in frozen salt can potentially provide a pathway for the release of active iodine to the polar atmosphere.
8
Peacock, Sarah, Travis S. Barman, Adam C. Schneider, Michaela Leung, Edward W. Schwieterman, Evgenya L. Shkolnik e R. O. Parke Loyd. "Accurate Modeling of Lyα Profiles and Their Impact on Photolysis of Terrestrial Planet Atmospheres". Astrophysical Journal 933, n.º 2 (1 de julho de 2022): 235. http://dx.doi.org/10.3847/1538-4357/ac77f2.
Resumo:
Abstract Accurately measuring and modeling the Lyα (Lyα; λ1215.67 Å) emission line from low-mass stars is vital for our ability to build predictive high energy stellar spectra, yet interstellar medium (ISM) absorption of this line typically prevents model-measurement comparisons. Lyα also controls the photodissociation of important molecules, like water and methane, in exoplanet atmospheres such that any photochemical models assessing potential biosignatures or atmospheric abundances require accurate Lyα host star flux estimates. Recent observations of three early M and K stars (K3, M0, M1) with exceptionally high radial velocities (>100 km s−1) reveal the intrinsic profiles of these types of stars as most of their Lyα flux is shifted away from the geocoronal line core and contamination from the ISM. These observations indicate that previous stellar spectra computed with the PHOENIX atmosphere code have underpredicted the core of Lyα in these types of stars. With these observations, we have been able to better understand the microphysics in the upper atmosphere and improve the predictive capabilities of the PHOENIX atmosphere code. Since these wavelengths drive the photolysis of key molecular species, we also present results analyzing the impact of the resulting changes to the synthetic stellar spectra on observable chemistry in terrestrial planet atmospheres.
9
Osajima, Josy Anteveli, Carla Cristina Schmitt Cavalheiro e Miguel Guillermo Neumann. "Changes in Molecular Weight of Poly(Styrenesulfonate) Initiated by Thioxanthone: Photolysis and Photo-Oxidation". Materials Science Forum 869 (agosto de 2016): 346–49. http://dx.doi.org/10.4028/www.scientific.net/msf.869.346.
Resumo:
The presence of dyes in colored polymers can cause a series of reactions that promote their photodegradation under irradiation. The aim of this study was to investigate the kinetic behavior of the photodegradation of poly (sodium 4-styrenesulfonate) (PSS) in aqueous solution or in the presence of thioxanthone (TX) under UV radiation in different atmospheres. These systems were monitored by SEC. The polydispersity decreased in all systems studied indicating that there was a breach of the polymer main chain. Only the PSS / TX / air atmosphere system peaked, which occured at 43h of irradiation. However, this system showed slower kinetics of polymeric scission due to the dye suppressing a transfer of energy from the triplet state to the polymer. The photodegradation of solutions of PSS / air atmosphere showed higher efficiency under ultraviolet radiation in relation to the PSS in the presence or absence of the dye under an inert atmosphere.
10
Moortgat, Geert K. "Important photochemical processes in the atmosphere". Pure and Applied Chemistry 73, n.º 3 (1 de janeiro de 2001): 487–90. http://dx.doi.org/10.1351/pac200173030487.
Resumo:
Among the many important roles played by ozone in the atmosphere is the role it plays in the generation of OH radicals, which are responsible for initiating the oxidation of a wide variety of atmospheric trace constituents. The OH production occurs dominantly from the formation of the excited O(1D) species in the UV photolysis of ozone, followed by the reaction of O(1D) with H2O vapor. The photochemistry of ozone is very complex, as the relatively weak bonds in ozone allow different states of the O and O2 photoproducts to be accessed. Recent detailed studies have now revealed that different photolysis channels are occurring in the 290375 nm spectral range, the region of importance for the generation of OH radicals in the lower atmosphere. The measured temperature-dependent quantum yields for the production of O(1D) atoms reflect the importance of the longer "wavelength tail" formation with regard to the enhanced OH production. Other significant atmospheric photolysis processes involving carbonyl compounds are reported. Direct photodissociation rates were measured in the outdoor photoreactor EUPHORE in Valencia and compared with model calculations. For most of the carbonyl compounds the effective quantum yields are significantly below unity.
11
Gen, Masao, Zhancong Liang, Ruifeng Zhang, Beatrix Rosette Go Mabato e Chak K. Chan. "Particulate nitrate photolysis in the atmosphere". Environmental Science: Atmospheres 2, n.º 2 (2022): 111–27. http://dx.doi.org/10.1039/d1ea00087j.
12
Prather, M. J. "Photolysis rates in correlated overlapping cloud fields: Cloud-J 7.3c". Geoscientific Model Development 8, n.º 8 (14 de agosto de 2015): 2587–95. http://dx.doi.org/10.5194/gmd-8-2587-2015.
Resumo:
Abstract. A new approach for modeling photolysis rates (J values) in atmospheres with fractional cloud cover has been developed and is implemented as Cloud-J – a multi-scattering eight-stream radiative transfer model for solar radiation based on Fast-J. Using observations of the vertical correlation of cloud layers, Cloud-J 7.3c provides a practical and accurate method for modeling atmospheric chemistry. The combination of the new maximum-correlated cloud groups with the integration over all cloud combinations by four quadrature atmospheres produces mean J values in an atmospheric column with root mean square (rms) errors of 4 % or less compared with 10–20 % errors using simpler approximations. Cloud-J is practical for chemistry–climate models, requiring only an average of 2.8 Fast-J calls per atmosphere vs. hundreds of calls with the correlated cloud groups, or 1 call with the simplest cloud approximations. Another improvement in modeling J values, the treatment of volatile organic compounds with pressure-dependent cross sections, is also incorporated into Cloud-J.
13
Prather, M. J. "Photolysis rates in correlated overlapping cloud fields: Cloud-J 7.3". Geoscientific Model Development Discussions 8, n.º 5 (27 de maio de 2015): 4051–73. http://dx.doi.org/10.5194/gmdd-8-4051-2015.
Resumo:
Abstract. A new approach for modeling photolysis rates (J values) in atmospheres with fractional cloud cover has been developed and implemented as Cloud-J – a multi-scattering eight-stream radiative transfer model for solar radiation based on Fast-J. Using observed statistics for the vertical correlation of cloud layers, Cloud-J 7.3 provides a practical and accurate method for modeling atmospheric chemistry. The combination of the new maximum-correlated cloud groups with the integration over all cloud combinations represented by four quadrature atmospheres produces mean J values in an atmospheric column with root-mean-square errors of 4% or less compared with 10–20% errors using simpler approximations. Cloud-J is practical for chemistry-climate models, requiring only an average of 2.8 Fast-J calls per atmosphere, vs. hundreds of calls with the correlated cloud groups, or 1 call with the simplest cloud approximations. Another improvement in modeling J values, the treatment of volatile organic compounds with pressure-dependent cross sections is also incorporated into Cloud-J.
14
Liu, Yuhan, Xuejiao Wang, Jing Shang, Weiwei Xu, Mengshuang Sheng e Chunxiang Ye. "The positive effect of formaldehyde on the photocatalytic renoxification of nitrate on TiO2 particles". Atmospheric Chemistry and Physics 22, n.º 17 (5 de setembro de 2022): 11347–58. http://dx.doi.org/10.5194/acp-22-11347-2022.
Resumo:
Abstract. Renoxification is the process of recycling NO3- / HNO3 into NOx under illumination and is mostly ascribed to the photolysis of nitrate. TiO2, a typical mineral dust component, is able to play a photocatalytic role in the renoxification process due to the formation of NO3 radicals; we define this process as “photocatalytic renoxification”. Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, may participate in the renoxification of nitrate-doped TiO2 particles. In this study, we established a 400 L environmental chamber reaction system capable of controlling 0.8 %–70 % relative humidity at 293 K with the presence of 1 or 9 ppm HCHO and 4 wt % nitrate-doped TiO2. The direct photolyses of both nitrate and NO3 radicals were excluded by adjusting the illumination wavelength so as to explore the effect of HCHO on the “photocatalytic renoxification”. It was found that NOx concentrations can reach up to more than 100 ppb for nitrate-doped TiO2 particles, while almost no NOx was generated in the absence of HCHO. Nitrate type, relative humidity and HCHO concentration were found to influence NOx release. It was suggested that substantial amounts of NOx were produced via the NO3-–NO3⚫–HNO3–NOx pathway, where TiO2 worked for converting “NO3-” to “NO3⚫ ”, that HCHO participated in the transformation of “NO3⚫ ” to “HNO3” through hydrogen abstraction, and that “HNO3” photolysis answered for mass NOx release. So, HCHO played a significant role in this “photocatalytic renoxification” process. These results were found based on simplified mimics for atmospheric mineral dust under specific experimental conditions, which might deviate from the real situation but illustrated the potential of HCHO to influence nitrate renoxification in the atmosphere. Our proposed reaction mechanism by which HCHO promotes photocatalytic renoxification is helpful for deeply understanding atmospheric photochemical processes and nitrogen cycling and could be considered for better fitting atmospheric model simulations with field observations in some specific scenarios.
15
Hodzic, A., S. Madronich, P. S. Kasibhatla, G. Tyndall, B. Aumont, J. L. Jimenez, J. Lee-Taylor e J. Orlando. "Organic photolysis reactions in tropospheric aerosols: effect on secondary organic aerosol formation and lifetime". Atmospheric Chemistry and Physics Discussions 15, n.º 6 (17 de março de 2015): 8113–49. http://dx.doi.org/10.5194/acpd-15-8113-2015.
Resumo:
Abstract. This study presents the first modeling estimates of the potential effect of gas- and particle-phase organic photolysis reactions on the formation and lifetime of secondary organic aerosols (SOA). Typically only photolysis of smaller organic molecules (e.g. formaldehyde) for which explicit data exist is included in chemistry-climate models. Here, we specifically examine the photolysis of larger molecules that actively partition between the gas and particle phases. The chemical mechanism generator GECKO-A is used to explicitly model SOA formation from α-pinene, toluene, and C12 and C16 n-alkane reactions with OH at low- and high-NOx. Simulations are conducted for typical mid-latitude conditions and a solar zenith angle of 45° (permanent daylight). The results show that after four days of chemical aging under those conditions (equivalent to eight days in the summer mid-latitudes), gas-phase photolysis leads to a moderate decrease in SOA yields i.e ~15% (low-NOx) to ~45% (high-NOx) for α-pinene, ~15% for toluene, ~25% for C12-alkane, and ~10% for C16-alkane. The small effect on low volatility n-alkanes such as C16-alkane is due to the rapid partitioning of early-generation products to the particle phase where they are assumed to be protected from gas-phase photolysis. Minor changes are found in the volatility distribution of organic products and in oxygen to carbon ratios. The decrease in SOA mass seems increasingly more important after a day of chemical processing, suggesting that most laboratory experiments are likely too short to quantify the effect of gas-phase photolysis on SOA yields. Our results also suggest that many molecules containing chromophores are preferentially partitioned into the particle phase before they can be photolyzed in the gas-phase. Given the growing experimental evidence that these molecules can undergo in-particle photolysis, we performed sensitivity simulations using an estimated SOA photolysis rate of JSOA=4 x 10-4JNO2. Modeling results indicate that this photolytic loss rate would decrease SOA mass by 40–60% for most species after ten days of equivalent atmospheric aging at mid-latitudes in the summer. It should be noted that in our simulations we do not consider in-particle or aqueous-phase reactions which could modify the chemical composition of the particle, and thus the amount of photolabile species. The atmospheric implications of our results are significant for both the SOA global distribution and lifetime. GEOS-Chem global model results suggest that particle-phase photolytic reactions could be an important loss process for SOA in the atmosphere, removing aerosols from the troposphere on timescales (less than 7 days) that are comparable to wet deposition.
16
Hodzic, A., S. Madronich, P. S. Kasibhatla, G. Tyndall, B. Aumont, J. L. Jimenez, J. Lee-Taylor e J. Orlando. "Organic photolysis reactions in tropospheric aerosols: effect on secondary organic aerosol formation and lifetime". Atmospheric Chemistry and Physics 15, n.º 16 (20 de agosto de 2015): 9253–69. http://dx.doi.org/10.5194/acp-15-9253-2015.
Resumo:
Abstract. This study presents the first modeling estimates of the potential effect of gas- and particle-phase organic photolysis reactions on the formation and lifetime of secondary organic aerosols (SOAs). Typically only photolysis of smaller organic molecules (e.g., formaldehyde) for which explicit data exist is included in chemistry–climate models. Here, we specifically examine the photolysis of larger molecules that actively partition between the gas and particle phases. The chemical mechanism generator GECKO-A is used to explicitly model SOA formation from α-pinene, toluene, and C12 and C16 n-alkane reactions with OH at low and high NOx. Simulations are conducted for typical mid-latitude conditions and a solar zenith angle of 45° (permanent daylight). The results show that after 4 days of chemical aging under those conditions (equivalent to 8 days in the summer mid-latitudes), gas-phase photolysis leads to a moderate decrease in SOA yields, i.e., ~15 % (low NOx) to ~45 % (high NOx) for α-pinene, ~15 % for toluene, ~25 % for C12 n-alkane, and ~10 % for C16 n-alkane. The small effect of gas-phase photolysis on low-volatility n-alkanes such as C16 n-alkane is due to the rapid partitioning of early-generation products to the particle phase, where they are protected from gas-phase photolysis. Minor changes are found in the volatility distribution of organic products and in oxygen to carbon ratios. The decrease in SOA mass is increasingly more important after a day of chemical processing, suggesting that most laboratory experiments are likely too short to quantify the effect of gas-phase photolysis on SOA yields. Our results also suggest that many molecules containing chromophores are preferentially partitioned into the particle phase before they can be photolyzed in the gas phase. Given the growing experimental evidence that these molecules can undergo in-particle photolysis, we performed sensitivity simulations using an empirically estimated SOA photolysis rate of JSOA = 4 × 10−4 JNO2. Modeling results indicate that this photolytic loss rate would decrease SOA mass by 40–60 % for most species after 10 days of equivalent atmospheric aging at mid-latitudes in the summer. It should be noted that in our simulations we do not consider in-particle or aqueous-phase reactions which could modify the chemical composition of the particle and thus the quantity of photolabile species. The atmospheric implications of our results are significant for both the SOA global distribution and lifetime. GEOS-Chem global model results suggest that particle-phase photolytic reactions could be an important loss process for SOA in the atmosphere, removing aerosols from the troposphere on timescales of less than 7 days that are comparable to wet deposition.
17
Yoshida, Tatsuya, Shohei Aoki, Yuichiro Ueno, Naoki Terada, Yuki Nakamura, Kimie Shiobara, Nao Yoshida, Hiromu Nakagawa, Shotaro Sakai e Shungo Koyama. "Strong Depletion of 13C in CO Induced by Photolysis of CO2 in the Martian Atmosphere, Calculated by a Photochemical Model". Planetary Science Journal 4, n.º 3 (1 de março de 2023): 53. http://dx.doi.org/10.3847/psj/acc030.
Resumo:
Abstract The isotopic signature of atmospheric carbon offers a unique tracer for the history of the Martian atmosphere and the origin of organic matter on Mars. The photolysis of CO2 is known to induce strong isotopic fractionation of the carbon between CO2 and CO. However, its effects on the carbon isotopic compositions in the Martian atmosphere remain uncertain. Here, we develop a 1D photochemical model to consider the isotopic fractionation via photolysis of CO2, to estimate the vertical profiles of the carbon isotopic compositions of CO and CO2 in the Martian atmosphere. We find that CO is depleted in 13C compared with CO2 at each altitude, due to the fractionation via CO2 photolysis: the minimum value of the δ 13C in CO is about −170‰ under the standard eddy diffusion setting. This result supports the hypothesis that fractionated atmospheric CO is responsible for the production of the 13C-depleted organic carbon in the Martian sediments detected by the Curiosity Rover, through the conversion of CO into organic materials and their deposition on the surface. The photolysis and transport-induced fractionation of CO that we report here leads to a ∼15% decrease in the amount of inferred atmospheric loss when combined with the present-day fractionation of the atmosphere and previous studies of carbon escape to space. The fractionated isotopic composition of CO in the Martian atmosphere may be observed by ExoMars Trace Gas Orbiter and ground-based telescopes, and the escaping ion species produced by the fractionated carbon-bearing species may be detected by the Martian Moons eXploration mission in the future.
18
Fu, Qian, Xiao Yun Liu, Qi Xin Zhuang, Jun Qian e Zhe Wen Han. "Study on the Photo-Degradation and Photo-Stabilization of Poly(p-Phenylene Benzobisoxazole)". Advanced Materials Research 183-185 (janeiro de 2011): 201–5. http://dx.doi.org/10.4028/www.scientific.net/amr.183-185.201.
Resumo:
As a kind of rig-rod-like polymer, poly(p-phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO materials, however, is limited due to its low sunlight stability. In this study, photolysis of PBO films was studied by infrared spectroscopy and molecular mass determination. It found that at the beginning of photolysis, the I.V. values of PBO almost did not changed. Then, it underwent fast decrease stage. Moreover, PBO degrade slowly in N2 atmosphere than in air atmosphere. The most likely photo-degradation mechanism was put forward. Attempts to stabilize PBO from photolysis were also investigated. It found that heat treatment could alleviate photo-degradation speed of PBO. Traditional light stabilizers showed a marginal effect on photolysis of PBO, whereas ferrocene dimethanol behaved better effect on the photo-stabilization of PBO.
19
Xue, Likun, Rongrong Gu, Tao Wang, Xinfeng Wang, Sandra Saunders, Donald Blake, Peter K. K. Louie et al. "Oxidative capacity and radical chemistry in the polluted atmosphere of Hong Kong and Pearl River Delta region: analysis of a severe photochemical smog episode". Atmospheric Chemistry and Physics 16, n.º 15 (8 de agosto de 2016): 9891–903. http://dx.doi.org/10.5194/acp-16-9891-2016.
Resumo:
Abstract. We analyze a photochemical smog episode to understand the oxidative capacity and radical chemistry of the polluted atmosphere in Hong Kong and the Pearl River Delta (PRD) region. A photochemical box model based on the Master Chemical Mechanism (MCM v3.2) is constrained by an intensive set of field observations to elucidate the budgets of ROx (ROx = OH+HO2+RO2) and NO3 radicals. Highly abundant radical precursors (i.e. O3, HONO and carbonyls), nitrogen oxides (NOx) and volatile organic compounds (VOCs) facilitate strong production and efficient recycling of ROx radicals. The OH reactivity is dominated by oxygenated VOCs (OVOCs), followed by aromatics, alkenes and alkanes. Photolysis of OVOCs (except for formaldehyde) is the dominant primary source of ROx with average daytime contributions of 34–47 %. HONO photolysis is the largest contributor to OH and the second-most significant source (19–22 %) of ROx. Other considerable ROx sources include O3 photolysis (11–20 %), formaldehyde photolysis (10–16 %), and ozonolysis reactions of unsaturated VOCs (3.9–6.2 %). In one case when solar irradiation was attenuated, possibly by the high aerosol loadings, NO3 became an important oxidant and the NO3-initiated VOC oxidation presented another significant ROx source (6.2 %) even during daytime. This study suggests the possible impacts of daytime NO3 chemistry in the polluted atmospheres under conditions with the co-existence of abundant O3, NO2, VOCs and aerosols, and also provides new insights into the radical chemistry that essentially drives the formation of photochemical smog in the high-NOx environment of Hong Kong and the PRD region.
20
Lary, D. J. "Atmospheric pseudohalogen chemistry". Atmospheric Chemistry and Physics Discussions 4, n.º 5 (16 de setembro de 2004): 5381–405. http://dx.doi.org/10.5194/acpd-4-5381-2004.
Resumo:
Abstract. There are at least three reasons why hydrogen cyanide is likely to be significant for atmospheric chemistry. The first is well known, HCN is a product and marker of biomass burning. However, if a detailed ion chemistry of lightning is considered then it is almost certain than in addition to lightning producing NOx, it also produces HOx and HCN. Unlike NOx and HOx, HCN is long-lived and could therefore be a useful marker of lightning activity. Observational evidence is considered to support this view. Thirdly, the chemical decomposition of HCN leads to the production of small amounts of CN and NCO. NCO can be photolyzed in the visible portion of the spectrum yielding N atoms. The production of N atoms is significant as it leads to the titration of nitrogen from the atmosphere via N+N→N2. Normally the only modelled source of N atoms is NO photolysis which happens largely in the UV Schumann-Runge bands. However, NCO photolysis occurs in the visible and so could be involved in titration of atmospheric nitrogen in the lower stratosphere and troposphere. HCN emission inventories are worthy of attention. The CN and NCO radicals have been termed pseudohalogens since the 1920s. They are strongly bound, univalent, radicals with an extensive and varied chemistry. The products of the atmospheric oxidation of HCN are NO, CO and O3. N+CH4 and N+CH3OH are found to be important sources of HCN. Including the pseudohalogen chemistry gives a small increase in ozone and total reactive nitrogen (NOy).
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Nilsson, E. J. K., J. A. Schmidt e M. S. Johnson. "Pressure dependent isotopic fractionation in the photolysis of formaldehyde-d<sub>2</sub>". Atmospheric Chemistry and Physics 14, n.º 2 (20 de janeiro de 2014): 551–58. http://dx.doi.org/10.5194/acp-14-551-2014.
Resumo:
Abstract. The isotope effects in formaldehyde photolysis are the key link between the δD of methane emissions and the δD of atmospheric in situ hydrogen production. A few recent studies have suggested that a pressure dependence in the isotopic fractionation can partly explain enrichment of deuterium with altitude in the atmosphere. The mechanism and the extent of this pressure dependency is, however, not adequately described. In the present work D2CO and H2CO were photolyzed in a static reaction chamber at bath gas pressures of 50, 200, 400, 600 and 1000 mbar; these experiments compliment and extend our earlier work with HDCO vs. H2CO. The UV lamps used for photolysis emit light at wavelengths that primarily dissociate formaldehyde into molecular products, CO and H2 or D2. The isotope effect k(H2CO)/k(D2CO) = 3.16 ± 0.03 at 1000 mbar is in good agreement with results from previous studies. Similarly to what was previously shown for k(H2CO)/k(HDCO), the isotope effect decreased as pressure decreased. In addition, a model was constructed using RRKM theory to calculate the lifetime of excited formaldehyde on the S0 surface, to investigate its role in the observed pressure dependent photolytic fractionation of deuterium. The model shows that part of the fractionation is a result of competition between the isotopologue dependent rates of unimolecular dissociation and collisional relaxation. We suggest that the remaining fractionation is due to isotope effects in the rate of the non-radiative transition from S1 to S0, which are not considered in the present model.
22
Chan, H. G., M. D. King e M. M. Frey. "The impact of parameterising light penetration into snow on the photochemical production of NO<sub>x</sub> and OH radicals in snow". Atmospheric Chemistry and Physics Discussions 15, n.º 6 (23 de março de 2015): 8609–46. http://dx.doi.org/10.5194/acpd-15-8609-2015.
Resumo:
Abstract. Snow photochemical processes drive production of chemical trace gases, including nitrogen oxides (NO and NO2), and HOx radicals in snowpacks which are then released to the lower atmosphere. Coupled atmosphere–snow modelling on global scales requires simple parameterisations of actinic flux in snow to reduce computational cost. The disagreement between a physical radiative transfer method and a method based upon the e-folding depth of light-in snow is evaluated. In particular for the photolysis of the nitrate anion (NO3-), the nitrite anion (NO2-) and hydrogen peroxide (H2O2) within snow and photolysis of gas-phase nitrogen dioxide (NO2) within the snowpack interstitial air are considered. The emission flux from the snowpack is estimated as the depth-integrated photolysis rate, v, calculated (a) explicitly with a physical radiative transfer model (TUV), vTUV and (b) with a simple parameterisation based on e-folding depth, vze. The evaluation is based upon the deviation of the ratio of depth-integrated photolysis rate determined by the two methods,vTUV/vze, from unity. The disagreement in depth-integrated photolysis rate between the RT model and e-folding depth parameterisation depends primarily on the photolysis action spectrum of chemical species, solar zenith angle and optical properties of the snowpack, (scattering cross-section and a weak dependence on light absorbing impurity (black carbon) and density). For photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 the ratio vTUV/vze varies within the range of 0.82–1.35, 0.88–1.28 and 0.92–1.27 respectively. The e-folding depth parameterisation underestimates for small solar zenith angles and overestimates at solar zenith angles around 60°. A simple algorithm has been developed to improve the parameterisation which reduced the ratio vTUV/vze to 0.97–1.02, 0.99–1.02 and 0.99–1.03 for photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 respectively. The e-folding depth parameterisation may give acceptable results for the photolysis of the NO3- anion and H2O2 in cold polar snow with large solar zenith angles, but can be improved by a correction based on solar zenith angle.
23
Bohn, B., e H. Zilken. "Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber". Atmospheric Chemistry and Physics Discussions 4, n.º 5 (29 de outubro de 2004): 6967–7010. http://dx.doi.org/10.5194/acpd-4-6967-2004.
Resumo:
Abstract. In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain 74% and 67% of external values for photolysis frequencies j(NO2) (NO2+hν→NO+O(3P)) and j(O1D) (O3+hν→O2+O(1D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65–0.86 and 0.60–0.73, for j(NO2) and j(O1D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR.
24
Bohn, B., e H. Zilken. "Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber". Atmospheric Chemistry and Physics 5, n.º 1 (25 de janeiro de 2005): 191–206. http://dx.doi.org/10.5194/acp-5-191-2005.
Resumo:
Abstract. In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain fractions of 0.74 and 0.67 of external values for photolysis frequencies j(NO2) (NO2+hν→NO+O(3P)) and j(O1D) (O3+hν→O2+O(1D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65-0.86 and 0.60-0.73, for j(NO2) and j(O1D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR.
25
Laufs, Sebastian, e Jörg Kleffmann. "Investigations on HONO formation from photolysis of adsorbed HNO3 on quartz glass surfaces". Physical Chemistry Chemical Physics 18, n.º 14 (2016): 9616–25. http://dx.doi.org/10.1039/c6cp00436a.
26
Davankov, V. A. "The Riddle of Atmospheric Oxygen: Photosynthesis or Photolysis?" Russian Journal of Physical Chemistry A 95, n.º 10 (outubro de 2021): 1963–70. http://dx.doi.org/10.1134/s0036024421100046.
Resumo:
Abstract The stoichiometry of the photosynthetic reaction requires that the quantities of the end products (organic biomaterial and free oxygen) be equal. However, the correct balance of the amounts of oxygen and organic matter that could have been produced by green plants on the land and in the ocean since the emergence of unique oxygenic photosynthetic systems (no more than 2.7 billion years ago) is virtually impossible, since the vast majority of oxygen was lost in oxidizing the initially reducing matter of the planet, and the bulk of organic carbon is scattered in sedimentary rocks. In recent decades, convincing information has been obtained in favor of the large-scale photolysis of water molecules in the upper atmosphere with the scattering of light hydrogen into space and the retention of heavier oxygen by gravity. This process has been operating continuously since the formation of the Earth. It is accompanied by huge losses of water and the oxidation of salts of ferrous iron and sulfide sulfur in the oceans and methane in the atmosphere. The main stages of the evolution of the atmosphere and surface layers of the Earth’s crust are analyzed for the first time in this work by considering the parallel processes of photosynthesis and photolysis. Large-scale photolysis of water also provides consistent explanations for the main stages in the evolution of the nearest planets of our Solar System.
27
Liu, Jiangping, Sheng Li, Jiafa Zeng, Majda Mekic, Zhujun Yu, Wentao Zhou, Gwendal Loisel et al. "Assessing indoor gas phase oxidation capacity through real-time measurements of HONO and NOxin Guangzhou, China". Environmental Science: Processes & Impacts 21, n.º 8 (2019): 1393–402. http://dx.doi.org/10.1039/c9em00194h.
28
Zhong, Xuelian, Hengqing Shen, Min Zhao, Ji Zhang, Yue Sun, Yuhong Liu, Yingnan Zhang et al. "Nitrous acid budgets in the coastal atmosphere: potential daytime marine sources". Atmospheric Chemistry and Physics 23, n.º 23 (30 de novembro de 2023): 14761–78. http://dx.doi.org/10.5194/acp-23-14761-2023.
Resumo:
Abstract. Nitrous acid (HONO), a vital precursor of atmospheric hydroxyl radicals (OH), has been extensively investigated to understand its characteristics and formation mechanisms. However, discerning fundamental mechanisms across diverse environments remains challenging. This study utilizes measurements from Mount Lao, a coastal mountain in eastern China, and an observation-based chemical box model (OBM) to examine HONO budgets and their subsequent impacts on atmospheric oxidizing capacity. The model incorporates additional HONO sources, including direct emissions, heterogeneous conversions of NO2 on aerosol and ground surfaces, and particulate nitrate photolysis. The observed mean HONO concentration was 0.46 ± 0.37 ppbv. The updated model reproduced daytime HONO concentrations well during dust and photochemical pollution events. During dust events, daytime HONO formation was dominated by photo-enhanced heterogeneous reactions of NO2 on aerosol surfaces (> 50 %), whereas particulate nitrate photolysis (34 %) prevailed during photochemical pollution events. Nevertheless, the model uncovers a significant unidentified marine HONO source in a “sea case”, with its HONO production rate reaching up to 0.70 ppbv h−1 at noon. Without considering this unidentified source, an extraordinarily high photolysis coefficient of nitrate and/or a heterogeneous uptake coefficient of NO2 would be required to match observed HONO concentrations. This missing marine HONO source affected the peak O3 production rate and OH radical concentration by 36 % and 28 %, respectively, at the observation site. Given the limited HONO observation data in coastal and marine settings, the unidentified HONO source may cause an underestimation of the atmosphere's oxidizing capacity. This study highlights the necessity for further investigation of the role of HONO in atmospheric chemistry in coastal and marine environments.
29
Dusanter, S., D. Vimal e P. S. Stevens. "Technical note: Measuring tropospheric OH and HO<sub>2</sub> by laser-induced fluorescence at low pressure. A comparison of calibration techniques". Atmospheric Chemistry and Physics 8, n.º 2 (25 de janeiro de 2008): 321–40. http://dx.doi.org/10.5194/acp-8-321-2008.
Resumo:
Abstract. The hydroxyl radical (OH) is one of the most important oxidants in the atmosphere, as it is involved in many reactions that affect regional air quality and global climate change. Because of its high reactivity, measurements of OH radical concentrations in the atmosphere are difficult, and often require careful calibrations that rely on the production of a known concentration of OH at atmospheric pressure. The Indiana University OH instrument, based on the Fluorescence Assay by Gas Expansion technique (FAGE), has been calibrated in the laboratory using two different approaches: the production of OH from the UV-photolysis of water-vapor, and the steady-state production of OH from the reaction of ozone with alkenes. The former technique relies on two different actinometric methods to measure the product of the lamp flux at 184.9 nm and the photolysis time. This quantity derived from N2O actinometry was found to be 1.5 times higher than that derived from O2 actinometry. The water photolysis and ozone-alkene techniques are shown to agree within their experimental uncertainties (respectively 17% and 44%), although the sensitivities derived from the ozone-alkene technique were systematically lower by 40% than those derived from the water-vapor UV- photolysis technique using O2 actinometry. The agreement between the two different methods improves the confidence of the water-vapor photolysis method as an accurate calibration technique for HOx instruments. Because several aspects of the mechanism of the gas phase ozonolysis of alkenes are still uncertain, this technique should be used with caution to calibrate OH instruments.
30
Nizkorodov, S. A., J. D. Crounse, J. L. Fry, C. M. Roehl e P. O. Wennberg. "Near-IR photodissociation of peroxy acetyl nitrate". Atmospheric Chemistry and Physics Discussions 4, n.º 2 (1 de março de 2004): 1269–89. http://dx.doi.org/10.5194/acpd-4-1269-2004.
Resumo:
Abstract. Measurements of the C-H overtone transition strengths combined with estimates of the photodissociation cross sections for these transitions suggest that near-IR photodissociation of peroxy acetyl nitrate (PAN) is less significant (Jnear-IR≈3×10−8s−1 at noon) in the lower atmosphere than competing sinks resulting from unimolecular decomposition and ultraviolet photolysis. This is in contrast to the photochemical behavior of a related peroxy nitrate, pernitric acid (PNA), that undergoes rapid near-IR photolysis in the atmosphere with Jnear-IR≈10−5s−1 at noon (Roehl et al., 2002). This difference is attributed to the larger binding energy and larger number of vibrational degrees of freedom in PAN, which make 4νCH the lowest overtone excitation with a high photodissociation yield (as opposed to 2νOH in PNA).
31
Nizkorodov, S. A., J. D. Crounse, J. L. Fry, C. M. Roehl e P. O. Wennberg. "Near-IR photodissociation of peroxy acetyl nitrate". Atmospheric Chemistry and Physics 5, n.º 2 (10 de fevereiro de 2005): 385–92. http://dx.doi.org/10.5194/acp-5-385-2005.
Resumo:
Abstract. Measurements of the C-H overtone transition strengths combined with estimates of the photodissociation cross sections for these transitions suggest that near-IR photodissociation of peroxy acetyl nitrate (PAN) is less significant (Jnear-IR≈3x10-8s-1 at noon) in the lower atmosphere than competing sinks resulting from unimolecular decomposition and ultraviolet photolysis. This is in contrast to the photochemical behavior of a related peroxy nitrate, pernitric acid (PNA), that undergoes rapid near-IR photolysis in the atmosphere with Jnear-IR≈10-5s-1 at noon (Roehl et al., 2002). This difference is attributed to the larger binding energy and larger number of vibrational degrees of freedom in PAN, which make 4νCH the lowest overtone excitation with a high photodissociation yield (as opposed to 2νOH in PNA).
32
Peng, Zhe, Julia Lee-Taylor, Harald Stark, John J. Orlando, Bernard Aumont e Jose L. Jimenez. "Evolution of OH reactivity in NO-free volatile organic compound photooxidation investigated by the fully explicit GECKO-A model". Atmospheric Chemistry and Physics 21, n.º 19 (4 de outubro de 2021): 14649–69. http://dx.doi.org/10.5194/acp-21-14649-2021.
Resumo:
Abstract. OH reactivity (OHR) is an important control on the oxidative capacity in the atmosphere but remains poorly constrained in many environments, such as remote, rural, and urban atmospheres, as well as laboratory experiment setups under low-NO conditions. For an improved understanding of OHR, its evolution during oxidation of volatile organic compounds (VOCs) is a major aspect requiring better quantification. We use the fully explicit Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) model to study the OHR evolution in the NO-free photooxidation of several VOCs, including decane (an alkane), m-xylene (an aromatic), and isoprene (an alkene). Oxidation progressively produces more saturated and functionalized species. Total organic OHR (including precursor and products, OHRVOC) first increases for decane (as functionalization increases OH rate coefficients) and m-xylene (as much more reactive oxygenated alkenes are formed). For isoprene, C=C bond consumption leads to a rapid drop in OHRVOC before significant production of the first main saturated multifunctional product, i.e., isoprene epoxydiol. The saturated multifunctional species in the oxidation of different precursors have similar average OHRVOC per C atom. The latter oxidation follows a similar course for different precursors, involving fragmentation of multifunctional species to eventual oxidation of C1 and C2 fragments to CO2, leading to a similar evolution of OHRVOC per C atom. An upper limit of the total OH consumption during complete oxidation to CO2 is roughly three per C atom. We also explore the trends in radical recycling ratios. We show that differences in the evolution of OHRVOC between the atmosphere and an environmental chamber, and between the atmosphere and an oxidation flow reactor (OFR), can be substantial, with the former being even larger, but these differences are often smaller than between precursors. The Teflon wall losses of oxygenated VOCs in chambers result in large deviations of OHRVOC from atmospheric conditions, especially for the oxidation of larger precursors, where multifunctional species may suffer substantial wall losses, resulting in significant underestimation of OHRVOC. For OFR, the deviations of OHRVOC evolution from the atmospheric case are mainly due to significant OHR contribution from RO2 and lack of efficient organic photolysis. The former can be avoided by lowering the UV lamp setting in OFR, while the latter is shown to be very difficult to avoid. However, the former may significantly offset the slowdown in fragmentation of multifunctional species due to lack of efficient organic photolysis.
33
Dusanter, S., D. Vimal e P. S. Stevens. "Technical Note: Measuring tropospheric OH and HO<sub>2</sub> by laser-induced fluorescence at low pressure – a comparison of calibration techniques". Atmospheric Chemistry and Physics Discussions 7, n.º 5 (4 de setembro de 2007): 12877–926. http://dx.doi.org/10.5194/acpd-7-12877-2007.
Resumo:
Abstract. The hydroxyl radical (OH) is one of the most important oxidants in the atmosphere, as it is involved in many reactions that affect regional air quality and global climate change. Because of its high reactivity, measurements of OH radical concentrations in the atmosphere are difficult, and often require careful calibrations that rely on the production of a known concentration of OH at atmospheric pressure. The Indiana University OH instrument, based on the Fluorescence Assay by Gas Expansion technique (FAGE), has been calibrated in the laboratory using two different approaches: the production of OH from the UV-photolysis of water-vapor, and the steady-state production of OH from the reaction of ozone with alkenes. Both techniques are shown to agree within their experimental uncertainties, although the sensitivities derived from the ozone-alkene technique were systematically lower than those derived from the water-vapor UV-photolysis technique. The agreement between the two different methods improves the confidence of the water-vapor photolysis method as an accurate calibration technique for HOx instruments. Because several aspects of the mechanism of the gas phase ozonolysis of alkenes are still uncertain, this technique should be used with caution to calibrate OH instruments.
34
Díaz-de-Mera, Yolanda, Alfonso Aranda, Alberto Notario, Ana Rodríguez, Diana Rodríguez e Iván Bravo. "Photolysis study of fluorinated ketones under natural sunlight conditions". Physical Chemistry Chemical Physics 17, n.º 35 (2015): 22991–98. http://dx.doi.org/10.1039/c5cp03527a.
35
Chan, H. G., M. D. King e M. M. Frey. "The impact of parameterising light penetration into snow on the photochemical production of NO<sub><i>x</i></sub> and OH radicals in snow". Atmospheric Chemistry and Physics 15, n.º 14 (17 de julho de 2015): 7913–27. http://dx.doi.org/10.5194/acp-15-7913-2015.
Resumo:
Abstract. Snow photochemical processes drive production of chemical trace gases in snowpacks, including nitrogen oxides (NOx = NO + NO2) and hydrogen oxide radical (HOx = OH + HO2), which are then released to the lower atmosphere. Coupled atmosphere–snow modelling of theses processes on global scales requires simple parameterisations of actinic flux in snow to reduce computational cost. The disagreement between a physical radiative-transfer (RT) method and a parameterisation based upon the e-folding depth of actinic flux in snow is evaluated. In particular, the photolysis of the nitrate anion (NO3-), the nitrite anion (NO2-) and hydrogen peroxide (H2O2) in snow and nitrogen dioxide (NO2) in the snowpack interstitial air are considered. The emission flux from the snowpack is estimated as the product of the depth-integrated photolysis rate coefficient, v, and the concentration of photolysis precursors in the snow. The depth-integrated photolysis rate coefficient is calculated (a) explicitly with an RT model (TUV), vTUV, and (b) with a simple parameterisation based on e-folding depth, vze. The metric for the evaluation is based upon the deviation of the ratio of the depth-integrated photolysis rate coefficient determined by the two methods, vTUV/vze, from unity. The ratio depends primarily on the position of the peak in the photolysis action spectrum of chemical species, solar zenith angle and physical properties of the snowpack, i.e. strong dependence on the light-scattering cross section and the mass ratio of light-absorbing impurity (i.e. black carbon and HULIS) with a weak dependence on density. For the photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 the ratio vTUV/vze varies within the range of 0.82–1.35, 0.88–1.28, 0.93–1.27 and 0.91–1.28 respectively. The e-folding depth parameterisation underestimates for small solar zenith angles and overestimates at solar zenith angles around 60° compared to the RT method. A simple algorithm has been developed to improve the parameterisation which reduces the ratio vTUV/vze to 0.97–1.02, 0.99–1.02, 0.99–1.03 and 0.98–1.06 for photolysis of NO2, the NO2- anion, the NO3- anion and H2O2 respectively. The e-folding depth parameterisation may give acceptable results for the photolysis of the NO3- anion and H2O2 in cold polar snow with large solar zenith angles, but it can be improved by a correction based on solar zenith angle and for cloudy skies.
36
Lieberman, Aaron, Julietta Picco, Murat Onder e Cort Anastasio. "Technical Note: A technique to convert NO2 to NO2− with S(IV) and its application to measuring nitrate photolysis". Atmospheric Chemistry and Physics 24, n.º 7 (16 de abril de 2024): 4411–19. http://dx.doi.org/10.5194/acp-24-4411-2024.
Resumo:
Abstract. Nitrate photolysis is a potentially significant mechanism for “renoxifying” the atmosphere, i.e., converting nitrate into nitrogen oxides – nitrogen dioxide (NO2) and nitric oxide (NO) – and nitrous acid (HONO). Nitrate photolysis in the environment occurs through two channels which produce (1) NO2 and hydroxyl radical (⚫OH) and (2) nitrite (NO2-) and an oxygen atom (O(3P)). Although the aqueous quantum yields and photolysis rate constants of both channels have been established, field observations suggest that nitrate photolysis is enhanced in the environment. Laboratory studies investigating these enhancements typically only measure one of the two photo-channels, since measuring both channels generally requires separate analytical methods and instrumentation. However, measuring only one channel makes it difficult to assess whether secondary chemistry is enhancing one channel at the expense of the other or if there is an overall enhancement of nitrate photochemistry. Here, we show that the addition of S(IV), i.e., bisulfite and sulfite, can convert NO2 to NO2-, allowing for measurement of both nitrate photolysis channels with the same equipment. By varying the concentration of S(IV) and exploring method parameters, we determine the experimental conditions that quantitatively convert NO2 and accurately quantify the resulting NO2-. We then apply the method to a test case, showing how an ⚫OH scavenger in solution prevents the oxidation of NO2- to NO2 but does not enhance the overall photolysis efficiency of nitrate.
37
Volkamer, R., P. Sheehy, L. T. Molina e M. J. Molina. "Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective". Atmospheric Chemistry and Physics 10, n.º 14 (30 de julho de 2010): 6969–91. http://dx.doi.org/10.5194/acp-10-6969-2010.
Resumo:
Abstract. A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA). During spring of 2003 (MCMA-2003 field campaign) an extensive set of measurements was collected to quantify time-resolved ROx (sum of OH, HO2, RO2) radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1) was constrained by measurements of (1) concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO), formaldehyde (HCHO), ozone (O3), glyoxal (CHOCHO), and other oxygenated volatile organic compounds (OVOCs); (2) respective photolysis-frequencies (J-values); (3) concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated) and oxidants, i.e., OH- and NO3 radicals, O3; and (4) NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; the MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Daytime radical production is found to be about 10–25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: Oxygenated VOC other than HCHO about 33%; HCHO and O3 photolysis each about 20%; O3/alkene reactions and HONO photolysis each about 12%, other sources <3%. Nitryl chloride photolysis could potentially contribute ~15% additional radicals, while NO2* + water makes – if any – a very small contribution (~2%). The peak radical production of ~7.5 107 molec cm−3 s−1 is found already at 10:00 a.m., i.e., more than 2.5 h before solar noon. O3/alkene reactions are indirectly responsible for ~33% of these radicals. Our measurements and analysis comprise a database that enables testing of the representation of radical sources and radical chain reactions in photochemical models. Since the photochemical processing of pollutants in the MCMA is radical limited, our analysis identifies the drivers for ozone and SOA formation. We conclude that reductions in VOC emissions provide an efficient opportunity to reduce peak concentrations of these secondary pollutants, because (1) about 70% of radical production is linked to VOC precursors; (2) lowering the VOC/NOx ratio has the further benefit of reducing the radical re-cycling efficiency from radical chain reactions (chemical amplification of radical sources); (3) a positive feedback is identified: lowering the rate of radical production from organic precursors also reduces that from inorganic precursors, like ozone, as pollution export from the MCMA caps the amount of ozone that accumulates at a lower rate inside the MCMA. Continued VOC reductions will in the future result in decreasing peak concentrations of ozone and SOA in the MCMA.
38
Roman, Claudiu, Cecilia Arsene, Iustinian Gabriel Bejan e Romeo Iulian Olariu. "Investigations into the gas-phase photolysis and OH radical kinetics of nitrocatechols: implications of intramolecular interactions on their atmospheric behaviour". Atmospheric Chemistry and Physics 22, n.º 4 (17 de fevereiro de 2022): 2203–19. http://dx.doi.org/10.5194/acp-22-2203-2022.
Resumo:
Abstract. The Environmental Simulation Chamber made of Quartz from the University “Alexandru Ioan Cuza” (ESC-Q-UAIC), at Iasi, Romania, was used to investigate the gas-phase reaction rate coefficients for four nitrocatechols toward OH radicals under simulated atmospheric conditions. Employing relative rate techniques at a temperature of 298 ± 2 K and a total air pressure of 1 atm, the obtained rate coefficients (in 10−12 cm3 s−1) were as follows: k3NCAT = (3.41 ± 0.37) for 3-nitrocatechol and k5M3NCAT = (5.55 ± 0.45) for 5-methyl-3-nitrocatechol at 365 nm, using CH3ONO photolysis as OH radicals source and dimethyl ether and cyclohexane as reference compounds, and k4NCAT = (1.27 ± 0.19) for 4-nitrocatechol and k4M5NCAT = (0.92 ± 0.14) for 4-methyl-5-nitrocatechol at 254 nm using H2O2 as OH radicals source and dimethyl ether and methanol as reference compounds. The photolysis rates in the actinic region, scaled to atmospheric relevant conditions by NO2 photolysis, were evaluated for 3-nitrocatechol and 5-methyl-3-nitrocatechol: J3NCAT = (3.06 ± 0.16) × 10−4 s−1 and J5M3NCAT = (2.14 ± 0.18) × 10−4 s−1, respectively. The photolysis rate constants at 254 nm were measured for 4-nitrocatechol and 4-methyl-5-nitrocatechol and the obtained values are J4NCAT = (6.7 ± 0.1) × 10−5 s−1 and J4M5NCAT = (3.2 ± 0.3) × 10−5 s−1. Considering the obtained results, our study suggests that photolysis may be the main degradation process for 3-nitrocatechol and 5-methyl-3-nitrocatechol in the atmosphere, with a photolytic lifetime in the atmosphere of up to 2 h. Results are discussed in terms of the reactivity of the four nitrocatechols under investigation toward OH-radical-initiated oxidation and their structural features. The rate coefficient values of the nitrocatechols are also compared with those estimated from the structure-activity relationship for monocyclic aromatic hydrocarbons and assessed in relation to their gas-phase IR spectra. Additional comparison with similar compounds is also presented, underlining the implications toward possible degradation pathways and atmospheric behaviour.
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Xue, L. K., T. Wang, H. Guo, D. R. Blake, J. Tang, X. C. Zhang, S. M. Saunders e W. X. Wang. "Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: results from the Mt. Waliguan Observatory". Atmospheric Chemistry and Physics 13, n.º 17 (2 de setembro de 2013): 8551–67. http://dx.doi.org/10.5194/acp-13-8551-2013.
Resumo:
Abstract. The chemistry of the natural atmosphere and the influence by long-range transport of air pollution are key issues in the atmospheric sciences. Here we present two intensive field measurements of volatile organic compounds (VOCs) in late spring and summer of 2003 at Mt. Waliguan (WLG, 36.28° N, 100.90° E, 3816 m a.s.l.), a baseline station in the northeast part of the Qinghai-Tibetan Plateau. Most VOC species exhibited higher concentrations in late spring than in summer. A typical diurnal variation was observed with higher nighttime levels, in contrast to results from other mountainous sites. Five different air masses were identified from backward trajectory analysis showing distinct VOC speciation. Air masses originating from the central Eurasian continent contained the lowest VOC levels compared to the others that were impacted by anthropogenic emissions from China and the Indian subcontinent. A photochemical box model based on the Master Chemical Mechanism (version 3.2) and constrained by a full suite of measurements was developed to probe the photochemistry of atmosphere at WLG. Our results show net ozone production from in situ photochemistry during both late spring and summer. Oxidation of nitric oxide (NO) by the hydroperoxyl radical (HO2) dominates the ozone production relative to the oxidation by the organic peroxy radicals (RO2), and the ozone is primarily destroyed by photolysis and reactions with the HOx (HOx = OH + HO2) radicals. Ozone photolysis is the predominant primary source of radicals (ROx = OH + HO2 + RO2), followed by the photolysis of secondary oxygenated VOCs and hydrogen peroxides. The radical losses are governed by the self and cross reactions among the radicals. Overall, the findings of the present study provide insights into the background chemistry and the impacts of pollution transport on the pristine atmosphere over the Eurasian continent.
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Fromont, Emeline F., John P. Ahlers, Laura N. R. do Amaral, Rory Barnes, Emily A. Gilbert, Elisa V. Quintana, Sarah Peacock, Thomas Barclay e Allison Youngblood. "Atmospheric Escape From Three Terrestrial Planets in the L 98-59 System". Astrophysical Journal 961, n.º 1 (1 de janeiro de 2024): 115. http://dx.doi.org/10.3847/1538-4357/ad0e0e.
Resumo:
Abstract A critically important process affecting the climate evolution and potential habitability of an exoplanet is atmospheric escape, in which high-energy radiation from a star drives the escape of hydrogen atoms and other light elements from a planet’s atmosphere. L 98-59 is a benchmark system for studying such atmospheric processes, with three transiting terrestrial-sized planets receiving Venus-like instellations (4–25 S ⊕) from their M3 host star. We use the VPLanet model to simulate the evolution of the L 98-59 system and the atmospheric escape of its inner three small planets, given different assumed initial water quantities. We find that, regardless of their initial water content, all three planets accumulate significant quantities of oxygen due to efficient water photolysis and hydrogen loss. All three planets also receive enough strong X-ray and extreme-ultraviolet flux to drive rapid water loss, which considerably affects their developing climates and atmospheres. Even in scenarios of low initial water content, our results suggest that the JWST will be sensitive to observations of retained oxygen on the L 98-59 planets in its future scheduled observations, with planets b and c being the most likely targets to possess an extended atmosphere. Our results constrain the atmospheric evolution of these small rocky planets, and they provide context for current and future observations of the L 98-59 system to generalize our understanding of multiterrestrial planet systems.
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Hsu, Juno, Michael J. Prather, Philip Cameron-Smith, Alex Veidenbaum e Alex Nicolau. "A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5". Geoscientific Model Development 10, n.º 7 (3 de julho de 2017): 2525–45. http://dx.doi.org/10.5194/gmd-10-2525-2017.
Resumo:
Abstract. Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere.The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere.Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.
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Chen, J., e P. Zhang. "Photodegradation of perfluorooctanoic acid in water under irradiation of 254 nm and 185 nm light by use of persulfate". Water Science and Technology 54, n.º 11-12 (1 de dezembro de 2006): 317–25. http://dx.doi.org/10.2166/wst.2006.731.
Resumo:
The photodegradation of perfluorooctanoic acid (PFOA) in water using two types of low-pressure mercury lamps, one emitting 254 nm and the other emitting 254 nm and 185 nm, by use of persulfate (K2S2O8) as an oxidant was investigated. PFOA was significantly decomposed under irradiation of 185 nm light, while it was very slow and negligible under 254 nm light irradiation. This was due to its strong absorption of PFOA from deep UV-region to 220 nm and a weak absorption from 220–460 nm. The addition of K2S2O8 led to efficient PFOA decomposition and defluorination no matter what light irradiation. Sulfate radical anion (SO−4), generated by photolysis of K2S2O8, initiated the oxidation of PFOA. Under irradiation of 185 nm light, PFOA was jointly decomposed through 185 nm light photolysis and initiation of sulfate radical. However, under irradiation of 254 nm light, PFOA decomposition was only initiated by sulfate radical. PFOA decomposed and defluorinated much faster under oxygen atmosphere than under nitrogen atmosphere, which suggested that oxygen molecules played an important role in PFOA decomposition.
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He, Shuzhong, Zhongming Chen e Xuan Zhang. "Photochemical reactions of methyl and ethyl nitrate: a dual role for alkyl nitrates in the nitrogen cycle". Environmental Chemistry 8, n.º 6 (2011): 529. http://dx.doi.org/10.1071/en10004.
Resumo:
Environmental contextAlkyl nitrates are considered to be important intermediates in the atmospheric hydrocarbons–nitrogen oxides–ozone cycle, which significantly determines air quality and nitrogen exchange between the atmosphere and the Earth’s surfaces. The present laboratory study investigates reaction products of alkyl nitrates to elucidate their photochemical reaction mechanisms in the atmosphere. The results provide a better understanding of the role played by alkyl nitrates in the atmospheric environment. AbstractAlkyl nitrates (ANs) are important nitrogen-containing organic compounds and are usually considered to be temporary reservoirs of reactive nitrogen NOx (NO2 and NO) in the atmosphere, although their atmospheric fates are incompletely understood. Here a laboratory study of the gas-phase photolysis and OH-initiated reactions of methyl nitrate (CH3ONO2) and ethyl nitrate (C2H5ONO2), as models of atmospheric ANs, is reported with a focus on elucidating the detailed photochemical reaction mechanisms of ANs in the atmosphere. A series of intermediate and end products were well characterised for the first time from the photochemical reactions of methyl and ethyl nitrate conducted under simulated atmospheric conditions. Notably, for both the photolysis and OH-initiated reactions of CH3ONO2 and C2H5ONO2, unexpectedly high yields of HNO3 (photochemically non-reactive nitrogen) were found and also unexpectedly high yields of peroxyacyl nitrates (RC(O)OONO2, where R = H, CH3, CH3CH2,…) (reactive nitrogen) have been found as CH3C(O)OONO2 in the C2H5ONO2 reaction or proposed as HC(O)OONO2 in the CH3ONO2 reaction. Although the yields of HNO3 from the ANs under ambient conditions are likely variable and different from those obtained in the laboratory experiments reported here, the results imply that the ANs could potentially serve as a sink for reactive nitrogen in the atmosphere. The potential for this dual role of organic nitrates in the nitrogen cycle should be considered in the study of air quality and nitrogen exchange between the atmosphere and surface. Finally, an attempt was made to estimate the production of HNO3 and peroxyacyl nitrates derived from NOx by ANs as intermediates in the atmosphere.
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Saiz-Lopez, A., R. W. Saunders, D. M. Joseph, S. H. Ashworth e J. M. C. Plane. "Absolute absorption cross-section and photolysis rate of I<sub>2</sub>". Atmospheric Chemistry and Physics 4, n.º 5 (1 de setembro de 2004): 1443–50. http://dx.doi.org/10.5194/acp-4-1443-2004.
Resumo:
Abstract. Following recent observations of molecular iodine (I2) in the coastal marine boundary layer (MBL) (Saiz-Lopez and Plane, 2004), it has become important to determine the absolute absorption cross-section of I2 at reasonably high resolution, and also to evaluate the rate of photolysis of the molecule in the lower atmosphere. The absolute absorption cross-section (σ) of gaseous I2 at room temperature and pressure (295K, 760Torr) was therefore measured between 182 and 750nm using a Fourier Transform spectrometer at a resolution of 4cm-1 (0.1nm at λ=500nm). The maximum absorption cross-section in the visible region was observed at λ=533.0nm to be σ=(4.24±0.50)x10-18cm2molecule-1. The spectrum is available as supplementary material accompanying this paper. The photo-dissociation rate constant (J) of gaseous I2 was also measured directly in a solar simulator, yielding J(I2)=0.12±0.03s-1 for the lower troposphere. This is in excellent agreement with the value of 0.12±0.015s-1 calculated using the measured absorption cross-section, terrestrial solar flux for clear sky conditions and assuming a photo-dissociation yield of unity. A two-stream radiation transfer model was then used to determine the variation in photolysis rate with solar zenith angle (SZA), from which an analytic expression is derived for use in atmospheric models. Photolysis appears to be the dominant loss process for I2 during daytime, and hence an important source of iodine atoms in the lower atmosphere.
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Volkamer, R., P. M. Sheehy, L. T. Molina e M. J. Molina. "Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective". Atmospheric Chemistry and Physics Discussions 7, n.º 2 (19 de abril de 2007): 5365–412. http://dx.doi.org/10.5194/acpd-7-5365-2007.
Resumo:
Abstract. A detailed analysis of OH, HO2 and RO2 radical sources is presented for the near field photochemical regime inside the Mexico City Metropolitan Area (MCMA). During spring of 2003 (MCMA-2003 field campaign) an extensive set of measurements was collected to quantify time resolved ROx (sum of OH, HO2, RO2) radical production rates from day- and nighttime radical sources. The Master Chemical Mechanism (MCMv3.1) was constrained by measurements of (1) concentration time-profiles of photosensitive radical precursors, i.e., nitrous acid (HONO), formaldehyde (HCHO), ozone (O3), glyoxal (CHOCHO), and other oxygenated volatile organic compounds (OVOCs); (2) respective photolysis-frequencies (J-values); (3) concentration time-profiles of alkanes, alkenes, and aromatic VOCs (103 compound are treated) and oxidants, i.e., OH- and NO3 radicals, O3; and (4) NO, NO2, meteorological and other parameters. The ROx production rate was calculated directly from these observations; MCM was used to estimate further ROx production from unconstrained sources, and express overall ROx production as OH-equivalents (i.e., taking into account the propagation efficiencies of RO2 and HO2 radicals into OH radicals). Daytime radical production is found to be about 10-25 times higher than at night; it does not track the abundance of sunlight. 12-h average daytime contributions of individual sources are: HCHO and O3 photolysis, each about 20%; O3/alkene reactions and HONO photolysis, each about 15%; unmeasured sources about 30%. While the direct contribution of O3/alkene reactions appears to be moderately small, source-apportionment of ambient HCHO and HONO identifies O3/alkene reactions as being largely responsible for jump-starting photochemistry about one hour after sunrise. The peak radical production is found to be higher than in any other urban influenced environment studied to date; further, differences exist in the timing of radical production. Our measurements and analysis comprise a database that enables testing of the representation of radical sources in photochemical models. Since the photochemical processing of pollutants is radical-limited in the MCMA, our analysis identifies the drivers for such processing. Three pathways are identified by which reductions in VOC emissions induce reductions in peak concentrations of secondary pollutants, such as O3 and secondary organic aerosol (SOA).
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Karagodin-Doyennel, Arseniy, Eugene Rozanov, Ales Kuchar, William Ball, Pavle Arsenovic, Ellis Remsberg, Patrick Jöckel et al. "The response of mesospheric H<sub>2</sub>O and CO to solar irradiance variability in models and observations". Atmospheric Chemistry and Physics 21, n.º 1 (11 de janeiro de 2021): 201–16. http://dx.doi.org/10.5194/acp-21-201-2021.
Resumo:
Abstract. Water vapor (H2O) is the source of reactive hydrogen radicals in the middle atmosphere, whereas carbon monoxide (CO), being formed by CO2 photolysis, is suitable as a dynamical tracer. In the mesosphere, both H2O and CO are sensitive to solar irradiance (SI) variability because of their destruction/production by solar radiation. This enables us to analyze the solar signal in both models and observed data. Here, we evaluate the mesospheric H2O and CO response to solar irradiance variability using the Chemistry-Climate Model Initiative (CCMI-1) simulations and satellite observations. We analyzed the results of four CCMI models (CMAM, EMAC-L90MA, SOCOLv3, and CESM1-WACCM 3.5) operated in CCMI reference simulation REF-C1SD in specified dynamics mode, covering the period from 1984–2017. Multiple linear regression analyses show a pronounced and statistically robust response of H2O and CO to solar irradiance variability and to the annual and semiannual cycles. For periods with available satellite data, we compared the simulated solar signal against satellite observations, namely the GOZCARDS composite for 1992–2017 for H2O and Aura/MLS measurements for 2005–2017 for CO. The model results generally agree with observations and reproduce an expected negative and positive correlation for H2O and CO, respectively, with solar irradiance. However, the magnitude of the response and patterns of the solar signal varies among the considered models, indicating differences in the applied chemical reaction and dynamical schemes, including the representation of photolyzes. We suggest that there is no dominating thermospheric influence of solar irradiance in CO, as reported in previous studies, because the response to solar variability is comparable with observations in both low-top and high-top models. We stress the importance of this work for improving our understanding of the current ability and limitations of state-of-the-art models to simulate a solar signal in the chemistry and dynamics of the middle atmosphere.
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Wu, Yanyou. "Is bicarbonate directly used as substrate to participate in photosynthetic oxygen evolution". Acta Geochimica 40, n.º 4 (21 de junho de 2021): 650–58. http://dx.doi.org/10.1007/s11631-021-00484-0.
Resumo:
AbstractIf the photosynthetic organisms assimilated only CO2 in the Archean atmosphere, hydroxide ion in the Archean seawater would not increase. If plants would not consume bicarbonate as a direct substrate during photosynthesis, it is difficult to explain the evolution of Earth's environment. To date, it is generally accepted that photosynthetic O2 evolution of plants come from water photolysis. However, it should be debated by evaluating the effect of bicarbonate in photosynthetic O2 evolution, analyzing the role of carbonic anhydrase (CA) in photosynthetic O2 evolution, and the relationship between thylakoid CA and photosynthetic O2 evolution. In the paper, I propose that bicarbonate is directly used as substrate to participate in photosynthetic O2 evolution. The rationality of bicarbonate photolysis of plants is discussed from the thermodynamics and evolution of Earth's environment. The isotopic evidence that bicarbonate is not the direct substrate of photosynthetic O2 release is reexamined, and the new explanation of bicarbonate photolysis in photosynthetic O2 evolution is proposed.
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Rohrer, F., B. Bohn, T. Brauers, D. Brüning, F. J. Johnen, A. Wahner e J. Kleffmann. "Characterisation of the photolytic HONO-source in the atmosphere simulation chamber SAPHIR". Atmospheric Chemistry and Physics 5, n.º 8 (12 de agosto de 2005): 2189–201. http://dx.doi.org/10.5194/acp-5-2189-2005.
Resumo:
Abstract. HONO formation has been proposed as an important OH radical source in simulation chambers for more than two decades. Besides the heterogeneous HONO formation by the dark reaction of NO2 and adsorbed water, a photolytic source has been proposed to explain the elevated reactivity in simulation chamber experiments. However, the mechanism of the photolytic process is not well understood so far. As expected, production of HONO and NOx was also observed inside the new atmospheric simulation chamber SAPHIR under solar irradiation. This photolytic HONO and NOx formation was studied with a sensitive HONO instrument under reproducible controlled conditions at atmospheric concentrations of other trace gases. It is shown that the photolytic HONO source in the SAPHIR chamber is not caused by NO2 reactions and that it is the only direct NOy source under illuminated conditions. In addition, the photolysis of nitrate which was recently postulated for the observed photolytic HONO formation on snow, ground, and glass surfaces, can be excluded in the chamber. A photolytic HONO source at the surface of the chamber is proposed which is strongly dependent on humidity, on light intensity, and on temperature. An empirical function describes these dependencies and reproduces the observed HONO formation rates to within 10%. It is shown that the photolysis of HONO represents the dominant radical source in the SAPHIR chamber for typical tropospheric O3/H2O concentrations. For these conditions, the HONO concentrations inside SAPHIR are similar to recent observations in ambient air.
49
Swartz, W. H., R. S. Stolarski, L. D. Oman, E. L. Fleming e C. H. Jackman. "Middle atmosphere response to different descriptions of the 11-yr solar cycle in spectral irradiance in a chemistry-climate model". Atmospheric Chemistry and Physics 12, n.º 13 (12 de julho de 2012): 5937–48. http://dx.doi.org/10.5194/acp-12-5937-2012.
Resumo:
Abstract. The 11-yr solar cycle in solar spectral irradiance (SSI) inferred from measurements by the SOlar Radiation & Climate Experiment (SORCE) suggests a much larger variation in the ultraviolet than previously accepted. We present middle atmosphere ozone and temperature responses to the solar cycles in SORCE SSI and the ubiquitous Naval Research Laboratory (NRL) SSI reconstruction using the Goddard Earth Observing System chemistry-climate model (GEOSCCM). The results are largely consistent with other recent modeling studies. The modeled ozone response is positive throughout the stratosphere and lower mesosphere using the NRL SSI, while the SORCE SSI produces a response that is larger in the lower stratosphere but out of phase with respect to total solar irradiance above 45 km. The modeled responses in total ozone are similar to those derived from satellite and ground-based measurements, 3–6 Dobson Units per 100 units of 10.7-cm radio flux (F10.7) in the tropics. The peak zonal mean tropical temperature response using the SORCE SSI is nearly 2 K per 100 units F10.7 – 3 times larger than the simulation using the NRL SSI. The GEOSCCM and the Goddard Space Flight Center (GSFC) 2-D coupled model are used to examine how the SSI solar cycle affects the atmosphere through direct solar heating and photolysis processes individually. Middle atmosphere ozone is affected almost entirely through photolysis, whereas the solar cycle in temperature is caused both through direct heating and photolysis feedbacks, processes that are mostly linearly separable. This is important in that it means that chemistry-transport models should simulate the solar cycle in ozone well, while general circulation models without coupled chemistry will underestimate the temperature response to the solar cycle significantly in the middle atmosphere. Further, the net ozone response results from the balance of ozone production at wavelengths less than 242 nm and destruction at longer wavelengths, coincidentally corresponding to the wavelength regimes of the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) and Spectral Irradiance Monitor (SIM) on SORCE, respectively. A higher wavelength-resolution analysis of the spectral response could allow for a better prediction of the atmospheric response to arbitrary SSI variations.
50
Rohrer, F., B. Bohn, T. Brauers, D. Brüning, F. J. Johnen, A. Wahner e J. Kleffmann. "Characterisation of the photolytic HONO-source in the atmosphere simulation chamber SAPHIR". Atmospheric Chemistry and Physics Discussions 4, n.º 6 (3 de dezembro de 2004): 7881–915. http://dx.doi.org/10.5194/acpd-4-7881-2004.
Resumo:
Abstract. HONO formation has been proposed as an important OH radical source in simulation chambers for more than two decades. Besides the heterogeneous HONO formation by the dark reaction of NO2 and adsorbed water, a photolytic source has been proposed to explain the elevated reactivity in simulation chamber experiments. However, the mechanism of the photolytic process is not well understood so far. As expected, production of HONO and NOx was also observed inside the new atmosphere simulation chamber SAPHIR under solar irradiation. This photolytic HONO and NOx formation was studied with a sensitive HONO instrument under reproducible controlled conditions at atmospheric concentrations of other trace gases. It is shown that the photolytic HONO source in the SAPHIR chamber is not caused by NO2 reactions and that it is the only direct NOy source under illuminated conditions. In addition, the photolysis of nitrate which was recently postulated for the observed photolytic HONO formation on snow, ground, and glass surfaces, can be excluded in the chamber. A photolytic HONO source at the surface of the chamber is proposed which is strongly dependent on humidity, on light intensity, and on temperature. An empirical function of the form S(HONO)=a1,2×J(NO2)×(1+(RH/RH0)2)×exp(−T0/T) describes these dependencies and reproduces the observed HONO formation rates to within 10%. It is shown that the photolysis of HONO represents the dominant radical source in the SAPHIR chamber for typical tropospheric O3/H2O concentrations. For these conditions, the HONO concentrations inside SAPHIR are similar to recent observations in ambient air.