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1
Beaver, M. R., M. J. Elrod, R. M. Garland e M. A. Tolbert. "Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation". Atmospheric Chemistry and Physics Discussions 6, n. 2 (28 marzo 2006): 2059–90. http://dx.doi.org/10.5194/acpd-6-2059-2006.
Testo completoAbstract (sommario):
Abstract. Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.
2
Beaver, M. R., M. J. Elrod, R. M. Garland e M. A. Tolbert. "Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation". Atmospheric Chemistry and Physics 6, n. 11 (4 agosto 2006): 3231–42. http://dx.doi.org/10.5194/acp-6-3231-2006.
Testo completoAbstract (sommario):
Abstract. Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.
3
Tsui, William G., Joseph L. Woo e V. Faye McNeill. "Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation". Atmosphere 10, n. 11 (31 ottobre 2019): 666. http://dx.doi.org/10.3390/atmos10110666.
Testo completoAbstract (sommario):
Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.
4
Liang, H., Z. M. Chen, D. Huang, Y. Zhao e Z. Y. Li. "Impacts of aerosols on the chemistry of atmospheric trace gases: a case study of peroxides and HO<sub>2</sub> radicals". Atmospheric Chemistry and Physics Discussions 13, n. 6 (20 giugno 2013): 16549–95. http://dx.doi.org/10.5194/acpd-13-16549-2013.
Testo completoAbstract (sommario):
Abstract. Field measurements of atmospheric peroxides were obtained during the summer on two consecutive years over urban Beijing, and focused on the impacts of aerosols on the chemistry of peroxide compounds and hydroperoxyl radicals (HO2). The major peroxides were determined to be hydrogen peroxide (H2O2), methyl hydroperoxide (MHP), and peroxyacetic acid (PAA). A negative correlation was found between H2O2 and PAA in rainwater, providing evidence for a conversion between H2O2 and PAA in the aqueous phase. A standard gas phase chemistry model based on the NCAR Master Mechanism provided a good reproduction of the observed H2O2 profile on non-haze days but greatly overpredicted the H2O2 level on haze days. We attribute this overprediction to the reactive uptake of HO2 by the aerosols, since there was greatly enhanced aerosol loading and aerosol liquid water content on haze days. The discrepancy between the observed and modeled H2O2 can be diminished by adding to the model a newly proposed transition metal ion catalytic mechanism of HO2 in aqueous aerosols. This confirms the importance of the aerosol uptake of HO2 and the subsequent aqueous phase reactions in the reduction of H2O2. The closure of HO2 and H2O2 between the gas and aerosol phases suggests that the aerosols do not have a net reactive uptake of H2O2, because the conversion of HO2 to H2O2 on aerosols compensates for the H2O2 loss. Laboratory studies for the aerosol uptake of H2O2 in the presence of HO2 are urgently required to better understand the aerosol uptake of H2O2 in the real atmosphere.
5
Liang, H., Z. M. Chen, D. Huang, Y. Zhao e Z. Y. Li. "Impacts of aerosols on the chemistry of atmospheric trace gases: a case study of peroxides and HO<sub>2</sub> radicals". Atmospheric Chemistry and Physics 13, n. 22 (20 novembre 2013): 11259–76. http://dx.doi.org/10.5194/acp-13-11259-2013.
Testo completoAbstract (sommario):
Abstract. Field measurements of atmospheric peroxides were obtained during the summer on two consecutive years over urban Beijing, which highlighted the impacts of aerosols on the chemistry of peroxide compounds and hydroperoxyl radicals (HO2). The major peroxides were determined to be hydrogen peroxide (H2O2), methyl hydroperoxide (MHP), and peroxyacetic acid (PAA). A negative correlation was found between H2O2 and PAA in rainwater, providing evidence for a conversion between H2O2 and PAA in the aqueous phase. A standard gas phase chemistry model based on the NCAR Master Mechanism provided a good reproduction of the observed H2O2 profile on non-haze days but greatly overpredicted the H2O2 level on haze days. We attribute this overprediction to the reactive uptake of HO2 by the aerosols, since there was greatly enhanced aerosol loading and aerosol liquid water content on haze days. The discrepancy between the observed and modeled H2O2 can be diminished by adding to the model a newly proposed transition metal ion catalytic mechanism of HO2 in aqueous aerosols. This confirms the importance of the aerosol uptake of HO2 and the subsequent aqueous phase reactions in the reduction of H2O2. The closure of HO2 and H2O2 between the gas and aerosol phases suggests that the aerosols do not have a net reactive uptake of H2O2, because the conversion of HO2 to H2O2 on aerosols compensates for the H2O2 loss. Laboratory studies for the aerosol uptake of H2O2 in the presence of HO2 are urgently required to better understand the aerosol uptake of H2O2 in the real atmosphere.
6
Morand, Gabriel, Pascale Chevallier, Cédric Guyon, Michael Tatoulian e Diego Mantovani. "In-Situ One-Step Direct Loading of Agents in Poly(acrylic acid) Coating Deposited by Aerosol-Assisted Open-Air Plasma". Polymers 13, n. 12 (10 giugno 2021): 1931. http://dx.doi.org/10.3390/polym13121931.
Testo completoAbstract (sommario):
In biomaterials and biotechnology, coatings loaded with bioactive agents are used to trigger biological responses by acting as drug release platforms and modulating surface properties. In this work, direct deposition of poly(acrylic acid) coatings containing various agents, such as dyes, fluorescent molecules, was achieved by aerosol-assisted open-air plasma. Using an original precursors injection strategy, an acrylic acid aerosol was loaded with an aqueous aerosol and deposited on silicon wafers. Results clearly showed that agents dissolved in the aqueous aerosol were successfully entrapped in the final coating. The effect of aerosols concentration, flow rate, and treatment time, on the coating morphology and the amount of entrapped agents, was also investigated. It was demonstrated that this process has the potential to entrap a tunable amount of any sensible water-soluble agent without altering its activity. To the best of our knowledge, this is the first time that the loading of an aqueous aerosol in coatings deposited by plasma from a liquid aerosol precursor is reported. This innovative approach complements plasma deposition of coatings loaded with bioactive agents from aqueous aerosols with the use of non-volatile liquid precursors.
7
Wilson, T. W., B. J. Murray, R. Wagner, O. Möhler, H. Saathoff, M. Schnaiter, J. Skrotzki et al. "Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures". Atmospheric Chemistry and Physics Discussions 12, n. 4 (10 aprile 2012): 8979–9033. http://dx.doi.org/10.5194/acpd-12-8979-2012.
Testo completoAbstract (sommario):
Abstract. Atmospheric secondary organic aerosol (SOA) is likely to exist in an ultra viscous or glassy state, particularly at low temperatures and humidities. It has also been shown that glassy aqueous citric acid aerosol is able to nucleate ice heterogeneously under conditions relevant to cirrus in the tropical tropopause layer (TTL). In this study we test if glassy aerosols with a range of chemical compositions heterogeneously nucleate ice under cirrus conditions. Three single component aqueous solution aerosols (raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA) and levoglucosan) and one multi component aqueous solution aerosol (raffinose mixed with five dicarboxylic acids and ammonium sulphate) were studied in both the liquid and glassy states at a large cloud simulation chamber. The investigated organic compounds have similar functionality to oxidised organic material found in atmospheric aerosol and have estimated temperature/humidity induced glass transition thresholds that fall within the range predicted for atmospheric SOA. All the aerosols tested were found to nucleate ice heterogeneously in the deposition mode at temperatures relevant to the TTL (<200 K). Raffinose and HMMA, which form glasses at higher temperatures, nucleated ice heterogeneously at temperatures as high as 214.6 and 218.5 K respectively. We present the calculated ice active surface site density, ns, of the aerosols tested here and also of glassy citric acid aerosol as a function of relative humidity with respect to ice (RHi). We also propose a parameterisation which can be used to estimate heterogeneous ice nucleation by glassy aerosol for use in cirrus cloud models up to ~220 K. Finally, we show that heterogeneous nucleation by glassy aerosol may compete with ice nucleation on mineral dust particles in mid-latitudes cirrus.
8
Ge, Xinlei, Qi Zhang, Yele Sun, Christopher R. Ruehl e Ari Setyan. "Effect of aqueous-phase processing on aerosol chemistry and size distributions in Fresno, California, during wintertime". Environmental Chemistry 9, n. 3 (2012): 221. http://dx.doi.org/10.1071/en11168.
Testo completoAbstract (sommario):
Environmental contextAqueous-phase processes in fogs and clouds can significantly alter atmospheric fine particles with consequences for climate and human health. We studied the influence of fog and rain on atmospheric aerosol properties, and show that aqueous-phase reactions contribute to the production of secondary aerosol species and change significantly the composition and microphysical properties of aerosols. In contrast, rains effectively remove aerosols and reduce their concentrations. AbstractSubmicrometre aerosols (PM1) were characterised in situ with a high resolution time-of-flight aerosol mass spectrometer and a scanning mobility particle sizer in Fresno, CA, from 9 to 23 January 2010. Three dense fog events occurred during the first week of the campaign whereas the last week was influenced by frequent rain events. We thus studied the effects of aqueous-phase processing on aerosol properties by examining the temporal variations of submicrometre aerosol composition and size distributions. Rains removed secondary species effectively, leading to low loadings of PM1 dominated by primary organic species. Fog episodes, however, increased the concentrations of secondary aerosol species (sulfate, nitrate, ammonium and oxygenated organic aerosol). The size distributions of these secondary species, which always showed a droplet mode peaking at ~500 nm in the vacuum aerodynamic diameter, increased in mode size during fog episodes as well. In addition, the oxygen-to-carbon ratio of oxygenated organic species increased in foggy days, indicating that fog processing likely enhances the production of secondary organic aerosol as well as its oxidation degree. Overall, our observations show that aqueous-phase processes significantly affect submicrometre aerosol chemistry and microphysics in the Central Valley of California during winter, responsible for the production of secondary inorganic and organic aerosol species and the formation of droplet mode particles, thus altering the climatic and health effects of ambient aerosols in this region.
9
Woo, J. L., e V. F. McNeill. "simpleGAMMA – a reduced model of secondary organic aerosol formation in the aqueous aerosol phase (aaSOA)". Geoscientific Model Development Discussions 8, n. 1 (22 gennaio 2015): 463–82. http://dx.doi.org/10.5194/gmdd-8-463-2015.
Testo completoAbstract (sommario):
Abstract. There is increasing evidence that the uptake and aqueous processing of water-soluble volatile organic compounds (VOCs) by wet aerosols or cloud droplets is an important source of secondary organic aerosol (SOA). We recently developed GAMMA (Gas–Aerosol Model for Mechanism Analysis), a zero-dimensional kinetic model that couples gas-phase and detailed aqueous-phase atmospheric chemistry for speciated prediction of SOA and organosulfate formation in cloudwater or aqueous aerosols. Results from GAMMA simulations of SOA formation in aerosol water (McNeill et al., 2012) indicate that it is dominated by two pathways: isoprene epoxydiol (IEPOX) uptake followed by ring-opening chemistry (under low-NOx conditions) and glyoxal uptake. This suggested that it is possible to model the majority of aqueous aerosol phase SOA mass using a highly simplified reaction scheme. We have therefore developed a reduced version of GAMMA, simpleGAMMA. Close agreement in predicted aaSOA mass is observed between simpleGAMMA and GAMMA under all conditions tested (between pH 1–4 and RH 40–80%) after 12 h of simulation. simpleGAMMA is computationally efficient and suitable for coupling with larger-scale atmospheric chemistry models.
10
Lim, Y. B., e B. J. Turpin. "Laboratory evidence of organic peroxide and peroxyhemiacetal formation in the aqueous phase and implications for aqueous OH". Atmospheric Chemistry and Physics 15, n. 22 (19 novembre 2015): 12867–77. http://dx.doi.org/10.5194/acp-15-12867-2015.
Testo completoAbstract (sommario):
Abstract. Aqueous chemistry in atmospheric waters (e.g., cloud droplets or wet aerosols) is considered a potentially important atmospheric pathway to produce secondary organic aerosol (SOAaq). Water-soluble organic compounds with small carbon numbers (C2–C3) are precursors for SOAaq; products include organic acids, organic sulfates, and high-molecular-weight compounds/oligomers. Fenton reactions and the uptake of gas-phase OH radicals are considered to be the major oxidant sources for aqueous organic chemistry. However, the sources and availability of oxidants in atmospheric waters are not well understood. The degree to which OH is produced in the aqueous phase affects the balance of radical and non-radical aqueous chemistry, the properties of the resulting aerosol, and likely its atmospheric behavior. This paper demonstrates organic peroxide formation during aqueous photooxidation of methylglyoxal using ultra-high-resolution Fourier transform ion cyclotron resonance electrospray ionization mass spectrometry (FTICR-MS). Organic peroxides are known to form through gas-phase oxidation of volatile organic compounds. They contribute secondary organic aerosol (SOA) formation directly by forming peroxyhemiacetals and epoxides (i.e., IEPOX), and indirectly by enhancing gas-phase oxidation through OH recycling. We provide simulation results of organic peroxide/peroxyhemiacetal formation in clouds and wet aerosols and discuss organic peroxides as a source of condensed-phase OH radicals and as a contributor to aqueous SOA.
11
Zobrist, B., C. Marcolli, D. A. Pedernera e T. Koop. "Do atmospheric aerosols form glasses?" Atmospheric Chemistry and Physics Discussions 8, n. 3 (22 maggio 2008): 9263–321. http://dx.doi.org/10.5194/acpd-8-9263-2008.
Testo completoAbstract (sommario):
Abstract. A new process is presented by which water-soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular diffusion practically ceases. The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous inorganic, organic and multi-component solutions are investigated with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose, raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulphate and mixtures of dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulphate (M5AS), of two polyols, of glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous solutions of the investigated inorganic solutes show Tg-values that are too low to be of atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form glasses at low but atmospherically relevant temperatures (≤230 K). To apply the laboratory data to the atmospheric situation, the measured phase transition temperatures were transformed from a concentration to a water activity scale by extrapolating water activities determined between 252 K and 313 K to lower temperatures. The obtained state diagrams reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher Tg of their respective solutions at a given water activity. To a lesser extent, Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol particles containing larger and more hydrophobic organic molecules (≳150 g mol-1) are more likely to form glasses at intermediate to high relative humidities in the upper troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be significantly impeded or even completely inhibited in organic-enriched aerosols at upper tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric relative humidity.
12
Zobrist, B., C. Marcolli, D. A. Pedernera e T. Koop. "Do atmospheric aerosols form glasses?" Atmospheric Chemistry and Physics 8, n. 17 (3 settembre 2008): 5221–44. http://dx.doi.org/10.5194/acp-8-5221-2008.
Testo completoAbstract (sommario):
Abstract. A new process is presented by which water soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular diffusion practically ceases. The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous inorganic, organic and multi-component solutions are investigated with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose, raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulfate and mixtures of dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulfate (M5AS), of two polyols, of glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous solutions of the investigated inorganic solutes show Tg values that are too low to be of atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form glasses at low but atmospherically relevant temperatures (≤230 K). To apply the laboratory data to the atmospheric situation, the measured phase transition temperatures were transformed from a concentration to a water activity scale by extrapolating water activities determined between 252 K and 313 K to lower temperatures. The obtained state diagrams reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher Tg of their respective solutions at a given water activity. To a lesser extent, Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol particles containing larger (≳150 g mol−1) and more hydrophobic organic molecules are more likely to form glasses at intermediate to high relative humidities in the upper troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be significantly impeded or even completely inhibited in organic-enriched aerosols at upper tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric relative humidity.
13
Rosanka, Simon, Holger Tost, Rolf Sander, Patrick Jöckel, Astrid Kerkweg e Domenico Taraborrelli. "How non-equilibrium aerosol chemistry impacts particle acidity: the GMXe AERosol CHEMistry (GMXe–AERCHEM, v1.0) sub-submodel of MESSy". Geoscientific Model Development 17, n. 7 (10 aprile 2024): 2597–615. http://dx.doi.org/10.5194/gmd-17-2597-2024.
Testo completoAbstract (sommario):
Abstract. Aqueous-phase chemical processes in clouds, fog, and deliquescent aerosols are known to alter atmospheric composition and acidity significantly. Traditionally, global and regional models predict aerosol composition by relying on thermodynamic equilibrium models and neglect non-equilibrium processes. Here, we present the AERosol CHEMistry (GMXe–AERCHEM, v1.0) sub-submodel developed for the Modular Earth Submodel System (MESSy) as an add-on to the thermodynamic equilibrium model (i.e. ISORROPIA-II) used by MESSy's Global Modal-aerosol eXtension (GMXe) submodel. AERCHEM allows the representation of non-equilibrium aqueous-phase chemistry of varying complexity in deliquescent fine aerosols. We perform a global simulation for the year 2010 by using the available detailed kinetic model for the chemistry of inorganic and small oxygenated organics. We evaluate AERCHEM's performance by comparing the simulated concentrations of sulfate, nitrate, ammonium, and chloride to in situ measurements of three monitoring networks. Overall, AERCHEM reproduces observed concentrations reasonably well. We find that, especially in the USA, the consideration of non-equilibrium chemistry in deliquescent aerosols reduces the model bias for sulfate, nitrate, and ammonium when compared to simulated concentrations by ISORROPIA-II. Over most continental regions, fine-aerosol acidity simulated by AERCHEM is similar to the predictions by ISORROPIA-II, but simulated aerosol acidity tends to be slightly lower in most regions. The consideration of non-equilibrium chemistry in deliquescent aerosols leads to a significantly higher aerosol acidity in the marine boundary layer, which is in line with observations and recent literature. AERCHEM allows an investigation of the global-scale impact of aerosol non-equilibrium chemistry on atmospheric composition. This will aid in the exploration of key multiphase processes and improve the model predictions for oxidation capacity and aerosols in the troposphere.
14
Lim, Y. B., e B. J. Turpin. "Organic peroxide and OH formation in aerosol and cloud water: laboratory evidence for this aqueous chemistry". Atmospheric Chemistry and Physics Discussions 15, n. 12 (25 giugno 2015): 17367–96. http://dx.doi.org/10.5194/acpd-15-17367-2015.
Testo completoAbstract (sommario):
Abstract. Aqueous chemistry in atmospheric waters (e.g., cloud droplets or wet aerosols) is well accepted as an atmospheric pathway to produce secondary organic aerosol (SOAaq). Water-soluble organic compounds with small carbon numbers (C2-C3) are precursors for SOAaq and products include organic acids, organic sulfates, and high molecular weight compounds/oligomers. Fenton reactions and the uptake of gas-phase OH radicals are considered to be the major oxidant sources for aqueous organic chemistry. However, the sources and availability of oxidants in atmospheric waters are not well understood. The degree to which OH is produced in the aqueous phase affects the balance of radical and non-radical aqueous chemistry, the properties of the resulting aerosol, and likely its atmospheric behavior. This paper demonstrates organic peroxide formation during aqueous photooxidation of methylglyoxal using ultra high resolution Fourier Transform Ion Cyclotron Resonance electrospray ionization mass spectrometry (FTICR-MS). Organic peroxides are known to form through gas-phase oxidation of volatile organic compounds. They contribute secondary organic aerosol (SOA) formation directly by forming peroxyhemiacetals, and epoxides, and indirectly by enhancing gas-phase oxidation through OH recycling. We provide simulation results of organic peroxide/peroxyhemiacetal formation in clouds and wet aerosols and discuss organic peroxides as a source of condensed-phase OH radicals and as a contributor to aqueous SOA.
15
Sukhapan, Jariya, e Peter Brimblecombe. "Ionic Surface Active Compounds in Atmospheric Aerosols". Scientific World JOURNAL 2 (2002): 1138–46. http://dx.doi.org/10.1100/tsw.2002.188.
Testo completoAbstract (sommario):
Surfactants in the atmosphere have several potential roles in atmospheric chemistry. They can form films on aqueous surfaces, which lowers the surface tension and possibly delays water evaporation and gaseous transportation across the aqueous interface. They can also increase the solubility of organic compounds in the aqueous phase. Recently, the decrease of surface tension in cloud growing droplets has been suggested as relevant to increases in the number of droplets of smaller size, potentially enhancing cloud albedo. Natural surfactants in the lung aid gas transfer and influence the dissolution rate of aerosol particles, so surfactants in atmospheric aerosols, once inhaled, may interact with pulmonary surfactants. Ambient aerosols were collected from the edge of Norwich, a small city in a largely agricultural region of England, and analysed for surfactants. Methylene blue, a conventional dye for detecting anionic surfactants, has been used as a colorimetric agent. The concentration of surfactants expressed as methylene blue active substances (MBAS) is in the range of 6–170 pmol m-3(air). A negative correlation with chloride aerosol indicates that these surfactants are probably not the well-known surfactants derived from marine spray. A more positive correlation with aerosol nitrate and gaseous NOxsupports an association with more polluted inland air masses. The surfactants found in aerosols seem to be relatively strong acids, compared with weaker acids such as the long-chain carboxylic acids previously proposed as atmospheric surfactants. Surfactants from the oxidation of organic materials (perhaps vegetation- or soil-derived) seem a likely source of these substances in the atmosphere.
16
Diaz, Daniel, Alejandra Carreon e David W. Hahn. "Analysis of Copper and Lead in Aerosols with Laser-Induced Breakdown Spectroscopy". Photonics 11, n. 12 (25 novembre 2024): 1112. http://dx.doi.org/10.3390/photonics11121112.
Testo completoAbstract (sommario):
Laser-induced breakdown spectroscopy (LIBS) was applied to the analysis of aerosolized Cu- and Pb-bearing particles generated from aqueous solutions. A nitrogen-driven nebulizer was utilized to aerosolize Cu- and Pb-spiked solutions. The liquid matrix of the aqueous droplets was evaporated before the LIBS analysis, and the remaining gas-phase analyte-rich aerosols were analyzed in a LIBS system that featured a 1064 nm Nd:YAG laser, a Czerny–Turner spectrometer, and an ICCD camera. The Cu and Pb concentrations in the aerosol streams were 0.26–1.29 ppm and 0.40–1.19 ppm, respectively. Laser diffraction and the particle size distributions of the aqueous aerosols were obtained to indirectly demonstrate the evaporation of the liquid matrix. Highly linear calibration curves (R2 = 0.995 for Cu and R2 = 0.987 for Pb) and acceptable limits of detection (2 ppb for Cu and 9 ppb for Pb) and quantification (5 ppb and 28 ppb) were obtained. The applications of the presented methodology include the near-real-time and in situ analysis of wastewater and gas-phase aerosols contaminated with heavy metals.
17
Woo, J. L., e V. F. McNeill. "simpleGAMMA v1.0 – a reduced model of secondary organic aerosol formation in the aqueous aerosol phase (aaSOA)". Geoscientific Model Development 8, n. 6 (22 giugno 2015): 1821–29. http://dx.doi.org/10.5194/gmd-8-1821-2015.
Testo completoAbstract (sommario):
Abstract. There is increasing evidence that the uptake and aqueous processing of water-soluble volatile organic compounds (VOCs) by wet aerosols or cloud droplets is an important source of secondary organic aerosol (SOA). We recently developed GAMMA (Gas–Aerosol Model for Mechanism Analysis), a zero-dimensional kinetic model that couples gas-phase and detailed aqueous-phase atmospheric chemistry for speciated prediction of SOA and organosulfate formation in cloud water or aqueous aerosols. Results from GAMMA simulations of SOA formation in aerosol water (aaSOA) (McNeill et al., 2012) indicate that it is dominated by two pathways: isoprene epoxydiol (IEPOX) uptake followed by ring-opening chemistry (under low-NOx conditions) and glyoxal uptake. This suggested that it is possible to model the majority of aaSOA mass using a highly simplified reaction scheme. We have therefore developed a reduced version of GAMMA, simpleGAMMA. Close agreement in predicted aaSOA mass is observed between simpleGAMMA and GAMMA under all conditions tested (between pH 1–4 and RH 40–80 %) after 12 h of simulation. simpleGAMMA is computationally efficient and suitable for coupling with larger-scale atmospheric chemistry models or analyzing ambient measurement data.
18
Zhang, Yan-Lin, Kimitaka Kawamura, Ping Qing Fu, Suresh K. R. Boreddy, Tomomi Watanabe, Shiro Hatakeyama, Akinori Takami e Wei Wang. "Aircraft observations of water-soluble dicarboxylic acids in the aerosols over China". Atmospheric Chemistry and Physics 16, n. 10 (25 maggio 2016): 6407–19. http://dx.doi.org/10.5194/acp-16-6407-2016.
Testo completoAbstract (sommario):
Abstract. Vertical profiles of dicarboxylic acids, related organic compounds and secondary organic aerosol (SOA) tracer compounds in particle phase have not yet been simultaneously explored in East Asia, although there is growing evidence that aqueous-phase oxidation of volatile organic compounds may be responsible for the elevated organic aerosols (OA) in the troposphere. Here, we found consistently good correlation of oxalic acid, the most abundant individual organic compounds in aerosols globally, with its precursors as well as biogenic-derived SOA compounds in Chinese tropospheric aerosols by aircraft measurements. Anthropogenically derived dicarboxylic acids (i.e., C5 and C6 diacids) at high altitudes were 4–20 times higher than those from surface measurements and even occasionally dominant over oxalic acid at altitudes higher than 2 km, which is in contrast to the predominance of oxalic acid previously reported globally including the tropospheric and surface aerosols. This indicates an enhancement of tropospheric SOA formation from anthropogenic precursors. Furthermore, oxalic acid-to-sulfate ratio maximized at altitudes of ∼ 2 km, explaining aqueous-phase SOA production that was supported by good correlations with predicted liquid water content, organic carbon and biogenic SOA tracers. These results demonstrate that elevated oxalic acid and related SOA compounds from both the anthropogenic and biogenic sources may substantially contribute to tropospheric OA burden over polluted regions of China, implying aerosol-associated climate effects and intercontinental transport.
19
Li, Tao, Zhe Wang, Yaru Wang, Chen Wu, Yiheng Liang, Men Xia, Chuan Yu et al. "Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong SAR". Atmospheric Chemistry and Physics 20, n. 1 (13 gennaio 2020): 391–407. http://dx.doi.org/10.5194/acp-20-391-2020.
Testo completoAbstract (sommario):
Abstract. To investigate the cloud water chemistry and the effects of cloud processing on aerosol properties, comprehensive field observations of cloud water, aerosols, and gas-phase species were conducted at a mountaintop site in Hong Kong SAR in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds (refer to aldehydes and acetone), carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 µeq L−1) was insufficient for neutralizing the dominant sulfate (231 µeq L−1) and nitrate (160 µeq L−1). Substantial DOM (9.3 mgC L−1) was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18 % and 6 % in carbon molar concentrations, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 µM; µM is equal to µmol L−1) and glyoxal (6.72 µM) were higher than that of formaldehyde (1.59 µM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls. Both organics and sulfate were significantly produced in cloud water, and the aqueous formation of organics was more enhanced by photochemistry and under less acidic conditions. Moreover, elevated sulfate and organics were measured in the cloud-processed aerosols, and they were expected to contribute largely to the increase in droplet-mode aerosol mass fraction. This study demonstrates the significant role of clouds in altering the chemical compositions and physical properties of aerosols via scavenging and aqueous chemical processing, providing valuable information about gas–cloud–aerosol interactions in subtropical and coastal regions.
20
Li, Z., A. N. Schwier, N. Sareen e V. F. McNeill. "Reactive processing of formaldehyde and acetaldehyde in aqueous aerosol mimics: surface tension depression and secondary organic products". Atmospheric Chemistry and Physics Discussions 11, n. 7 (7 luglio 2011): 19477–506. http://dx.doi.org/10.5194/acpd-11-19477-2011.
Testo completoAbstract (sommario):
Abstract. The reactive uptake of carbonyl-containing volatile organic compounds (cVOCs) by aqueous atmospheric aerosols is a likely source of particulate organic material. The aqueous-phase secondary organic products of some cVOCs are surface-active. Therefore, cVOC uptake can lead to organic film formation at the gas-aerosol interface and changes in aerosol surface tension. We examined the chemical reactions of two abundant cVOCs, formaldehyde and acetaldehyde, in water and aqueous ammonium sulfate (AS) solutions mimicking tropospheric aerosols. Secondary organic products were identified using Aerosol Chemical Ionization Mass Spectrometry (Aerosol-CIMS), and changes in surface tension were monitored using pendant drop tensiometry. Hemiacetal oligomers and aldol condensation products were identified using Aerosol-CIMS. A hemiacetal sulfate ester was tentatively identified in the formaldehyde-AS system. Acetaldehyde depresses surface tension to 65(±2) dyn cm−1 in pure water and 62(±1) dyn cm−1 in AS solutions. Surface tension depression by formaldehyde in pure water is negligible; in AS solutions, a 9 % reduction in surface tension is observed. Mixtures of these species were also studied in combination with methylglyoxal in order to evaluate the influence of cross-reactions on surface tension depression and product formation in these systems. We find that surface tension depression in the solutions containing mixed cVOCs exceeds that predicted by an additive model based on the single-species isotherms.
21
Chen, Weihua, Xuemei Wang, Jason Blake Cohen, Shengzhen Zhou, Zhisheng Zhang, Ming Chang e Chuen-Yu Chan. "Properties of aerosols and formation mechanisms over southern China during the monsoon season". Atmospheric Chemistry and Physics 16, n. 20 (28 ottobre 2016): 13271–89. http://dx.doi.org/10.5194/acp-16-13271-2016.
Testo completoAbstract (sommario):
Abstract. Measurements of size-resolved aerosols from 0.25 to 18 µm were conducted at three sites (urban, suburban and background sites) and used in tandem with an atmospheric transport model to study the size distribution and formation of atmospheric aerosols in southern China during the monsoon season (May–June) in 2010. The mass distribution showed the majority of chemical components were found in the smaller size bins (< 2.5 µm). Sulfate was found to be strongly correlated with aerosol water and anticorrelated with atmospheric SO2, hinting at aqueous-phase reactions being the main formation pathway. Nitrate was the only major species that showed a bimodal distribution at the urban site and was dominated by the coarse mode in the other two sites, suggesting that an important component of nitrate formation is chloride depletion of sea salt transported from the South China Sea. In addition to these aqueous-phase reactions and interactions with sea salt aerosols, new particle formation, chemical aging, and long-range transport from upwind urban or biomass burning regions was also found to be important in at least some of the sites on some of the days. This work therefore summarizes the different mechanisms that significantly impact the aerosol chemical composition during the monsoon over southern China.
22
Li, Z., A. N. Schwier, N. Sareen e V. F. McNeill. "Reactive processing of formaldehyde and acetaldehyde in aqueous aerosol mimics: surface tension depression and secondary organic products". Atmospheric Chemistry and Physics 11, n. 22 (22 novembre 2011): 11617–29. http://dx.doi.org/10.5194/acp-11-11617-2011.
Testo completoAbstract (sommario):
Abstract. The reactive uptake of carbonyl-containing volatile organic compounds (cVOCs) by aqueous atmospheric aerosols is a likely source of particulate organic material. The aqueous-phase secondary organic products of some cVOCs are surface-active. Therefore, cVOC uptake can lead to organic film formation at the gas-aerosol interface and changes in aerosol surface tension. We examined the chemical reactions of two abundant cVOCs, formaldehyde and acetaldehyde, in water and aqueous ammonium sulfate (AS) solutions mimicking tropospheric aerosols. Secondary organic products were identified using Aerosol Chemical Ionization Mass Spectrometry (Aerosol-CIMS), and changes in surface tension were monitored using pendant drop tensiometry. Hemiacetal oligomers and aldol condensation products were identified using Aerosol-CIMS. Acetaldehyde depresses surface tension to 65(±2) dyn cm−1 in pure water (a 10% surface tension reduction from that of pure water) and 62(±1) dyn cm−1 in AS solutions (a 20.6% reduction from that of a 3.1 M AS solution). Surface tension depression by formaldehyde in pure water is negligible; in AS solutions, a 9% reduction in surface tension is observed. Mixtures of these species were also studied in combination with methylglyoxal in order to evaluate the influence of cross-reactions on surface tension depression and product formation in these systems. We find that surface tension depression in the solutions containing mixed cVOCs exceeds that predicted by an additive model based on the single-species isotherms.
23
Lim, Yong Bin, Hwajin Kim, Jin Young Kim e Barbara J. Turpin. "Photochemical organonitrate formation in wet aerosols". Atmospheric Chemistry and Physics 16, n. 19 (11 ottobre 2016): 12631–47. http://dx.doi.org/10.5194/acp-16-12631-2016.
Testo completoAbstract (sommario):
Abstract. Water is the most abundant component of atmospheric fine aerosol. However, despite rapid progress, multiphase chemistry involving wet aerosols is still poorly understood. In this work, we report results from smog chamber photooxidation of glyoxal- and OH-containing ammonium sulfate or sulfuric acid particles in the presence of NOx and O3 at high and low relative humidity. Particles were analyzed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). During the 3 h irradiation, OH oxidation products of glyoxal that are also produced in dilute aqueous solutions (e.g., oxalic acids and tartaric acids) were formed in both ammonium sulfate (AS) aerosols and sulfuric acid (SA) aerosols. However, the major products were organonitrogens (CHNO), organosulfates (CHOS), and organonitrogen sulfates (CHNOS). These were also the dominant products formed in the dark chamber, indicating non-radical formation. In the humid chamber (> 70 % relative humidity, RH), two main products for both AS and SA aerosols were organonitrates, which appeared at m ∕ z− 147 and 226. They were formed in the aqueous phase via non-radical reactions of glyoxal and nitric acid, and their formation was enhanced by photochemistry because of the photochemical formation of nitric acid via reactions of peroxy radicals, NOx and OH during the irradiation.
24
Wilson, T. W., B. J. Murray, R. Wagner, O. Möhler, H. Saathoff, M. Schnaiter, J. Skrotzki et al. "Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures". Atmospheric Chemistry and Physics 12, n. 18 (25 settembre 2012): 8611–32. http://dx.doi.org/10.5194/acp-12-8611-2012.
Testo completoAbstract (sommario):
Abstract. Atmospheric secondary organic aerosol (SOA) is likely to exist in a semi-solid or glassy state, particularly at low temperatures and humidities. Previously, it has been shown that glassy aqueous citric acid aerosol is able to nucleate ice heterogeneously under conditions relevant to cirrus in the tropical tropopause layer (TTL). In this study we test if glassy aerosol distributions with a range of chemical compositions heterogeneously nucleate ice under cirrus conditions. Three single component aqueous solution aerosols (raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA) and levoglucosan) and one multi component aqueous solution aerosol (raffinose mixed with five dicarboxylic acids and ammonium sulphate) were studied in both the liquid and glassy states at a large cloud simulation chamber. The investigated organic compounds have similar functionality to oxidised organic material found in atmospheric aerosol and have estimated temperature/humidity induced glass transition thresholds that fall within the range predicted for atmospheric SOA. A small fraction of aerosol particles of all compositions were found to nucleate ice heterogeneously in the deposition mode at temperatures relevant to the TTL (<200 K). Raffinose and HMMA, which form glasses at higher temperatures, nucleated ice heterogeneously at temperatures as high as 214.6 and 218.5 K respectively. We present the calculated ice active surface site density, ns, of the aerosols tested here and also of glassy citric acid aerosol as a function of relative humidity with respect to ice (RHi). We also propose a parameterisation which can be used to estimate heterogeneous ice nucleation by glassy aerosol for use in cirrus cloud models up to ~220 K. Finally, we show that heterogeneous nucleation by glassy aerosol may compete with ice nucleation on mineral dust particles in mid-latitudes cirrus.
25
Xu, Weiqi, Ye Kuang, Wanyun Xu, Zhiqiang Zhang, Biao Luo, Xiaoyi Zhang, Jiangchuang Tao, Hongqin Qiao, Li Liu e Yele Sun. "Hygroscopic growth and activation changed submicron aerosol composition and properties in the North China Plain". Atmospheric Chemistry and Physics 24, n. 16 (28 agosto 2024): 9387–99. http://dx.doi.org/10.5194/acp-24-9387-2024.
Testo completoAbstract (sommario):
Abstract. Aerosol hygroscopic growth and activation under high-relative-humidity (RH) conditions significantly influence the physicochemical properties of submicron aerosols (PM1). However, this process remains poorly characterized due to limited measurements. To address this gap, we deployed an advanced aerosol–fog sampling system that automatically switched between PM1, PM2.5 and total suspended particulate (TSP) inlets at a rural site in the North China Plain in the cold season. The results revealed that aerosol swelling due to water vapor uptake influenced aerosol sampling under high-RH conditions by shifting the cut-off size of impactors. At subsaturated high RH (> 90 %), over 25 % of aerosol mass with dry diameters below 1 µm resided in supermicron ranges, while in supersaturated foggy conditions, more than 70 % of submicron aerosol migrated to supermicron ranges. Hygroscopic growth and activation particularly affected highly hydrophilic inorganic salts, shifting a significant number of submicron sulfate and nitrate particles to supermicron ranges, with 27 %–33 % at 95 % ≤ RH ≤ 99 % and more than 78 % under supersaturated foggy conditions. Moreover, more than 10 % of submicron biomass burning organic aerosols grew beyond 2.5 µm during fog events, while fossil-fuel-related organic aerosol (FFOA) remained dominantly in submicron ranges, suggesting inefficient aqueous conversion of FFOA. The two secondary organic aerosol (SOA) factors (OOA1 and OOA2) behaved differently under supersaturated conditions, with OOA2 exhibiting a higher activated fraction despite a lower oxygen / carbon ratio. A substantial increase in organic nitrate and organosulfur mass concentrations in activated droplets during fog events suggested aqueous conversions and formations of brown carbon with potential radiative impacts. Overall, our study highlights remarkably different cloud and fog processing behaviors between primary and secondary aerosols, which would benefit a better understanding of aerosol–cloud interactions under distinct atmospheric conditions.
26
Daellenbach, Kaspar R., Jing Cai, Simo Hakala, Lubna Dada, Chao Yan, Wei Du, Lei Yao et al. "Substantial contribution of transported emissions to organic aerosol in Beijing". Nature Geoscience 17, n. 8 (agosto 2024): 747–54. http://dx.doi.org/10.1038/s41561-024-01493-3.
Testo completoAbstract (sommario):
AbstractHaze in Beijing is linked to atmospherically formed secondary organic aerosol, which has been shown to be particularly harmful to human health. However, the sources and formation pathways of these secondary aerosols remain largely unknown, hindering effective pollution mitigation. Here we have quantified the sources of organic aerosol via direct near-molecular observations in central Beijing. In winter, organic aerosol pollution arises mainly from fresh solid-fuel emissions and secondary organic aerosols originating from both solid-fuel combustion and aqueous processes, probably involving multiphase chemistry with aromatic compounds. The most severe haze is linked to secondary organic aerosols originating from solid-fuel combustion, transported from the Beijing–Tianjing–Hebei Plain and rural mountainous areas west of Beijing. In summer, the increased fraction of secondary organic aerosol is dominated by aromatic emissions from the Xi’an–Shanghai–Beijing region, while the contribution of biogenic emissions remains relatively small. Overall, we identify the main sources of secondary organic aerosol affecting Beijing, which clearly extend beyond the local emissions in Beijing. Our results suggest that targeting key organic precursor emission sectors regionally may be needed to effectively mitigate organic aerosol pollution.
27
Bao, Zhier, Xinyi Zhang, Qing Li, Jiawei Zhou, Guangming Shi, Li Zhou, Fumo Yang et al. "Measurement report: Intensive biomass burning emissions and rapid nitrate formation drive severe haze formation in the Sichuan Basin, China – insights from aerosol mass spectrometry". Atmospheric Chemistry and Physics 23, n. 2 (23 gennaio 2023): 1147–67. http://dx.doi.org/10.5194/acp-23-1147-2023.
Testo completoAbstract (sommario):
Abstract. Haze pollution is a severe environmental problem, caused by elevation of fine particles (aerodynamic diameter <2.5 µm, PM2.5), which is related to secondary aerosol formation, unfavourable synoptic conditions and regional transport, etc. The regional haze formation in basin areas, along with intensive emission of precursors, high relative humidity and poor dispersion conditions, is still limitedly understood. In this study, a field campaign was conducted to investigate the factors resulting in haze formation in the Sichuan Basin (SCB) during winter in 2021. The fine aerosol chemical composition was characterised using a time-of-flight aerosol chemical speciation monitor (ToF-ACSM), which also provided detailed information on the sources for organic aerosols (OAs). The average concentration of non-refractory fine particles (NR-PM2.5) was 98.5±38.7 µg m−3, and organics aerosols, nitrate, sulfate, ammonium and chloride took up 40.3 %, 28.8 %, 10.6 %, 15.3 % and 5.1 % of PM2.5. Three factors, including a hydrocarbon-like OA (HOA), a biomass burning OA (BBOA) and an oxygenated OA (OOA), were identified by applying the positive matrix factorisation (PMF) analysis, and they constituted 24.2 %, 24.2 % and 51.6 % of OA on average, respectively. Nitrate formation was promoted by gas-phase and aqueous-phase oxidation, while sulfate was mainly formed through aqueous-phase process. OOA showed strong dependence on Ox, demonstrating the contribution of photooxidation to OOA formation. OOA concentration increased as aerosol liquid water content (ALWC) increased within 200 µg m−3 and kept relatively constant when ALWC >200 µg m−3, suggesting the insignificant effect of aqueous-phase reactions on OOA formation. Among the three haze episodes identified during the whole campaign, the driving factors were different: the first haze episode (H1) was driven by nitrate formation through photochemical and aqueous-phase reactions, and the second haze episode (H2) was mainly driven by the intense emission of primary organic aerosols from biomass burning and vehicle exhaust, while the third haze episode (H3) was mainly driven by reactions involving nitrate formation and biomass burning emission. HOA and BBOA were scavenged, while OOA, nitrate and sulfate formation was enhanced by aqueous-phase reactions during fog periods, which resulted in the increase of O:C from pre-fog to post-fog periods. This study revealed the factors driving severe haze formation in the SCB and implied the benefit of controlling nitrate as well as intense biomass burning and vehicle exhaust emission for the mitigation of heavy aerosol pollution in this region.
28
Reid, Jonathan P., e Robert M. Sayer. "Chemistry in the Clouds: The Role of Aerosols in Atmospheric Chemistry". Science Progress 85, n. 3 (agosto 2002): 263–96. http://dx.doi.org/10.3184/003685002783238807a.
Testo completoAbstract (sommario):
Ever since the discovery of the ozone hole over the Antarctic and the recognition of the damaging effects of acid rain, the role of atmospheric aerosol particles in determining the chemical balance of the atmosphere has received much attention. Aerosol particles produced in combustion can also have a deleterious effect on human health. In this article we review the chemistry that can occur on aerosol particles, particularly on aqueous based aerosols in the troposphere. The sources, transformation and loss mechanisms of atmospheric aerosol will be discussed. In particular, we will focus on the role of chemical transformation on aerosol particles in promoting reactions that would otherwise be too slow in the homogeneous atmospheric gas phase. Heterogeneous reaction mechanisms of some key chemical reactions will be described. Recent observations of a high organic content of tropospheric aerosol particles will be described and a model of organic coated aerosols will be reviewed.
29
Lin, G., J. E. Penner, S. Sillman, D. Taraborrelli e J. Lelieveld. "Global mechanistic model of SOA formation: effects of different chemical mechanisms". Atmospheric Chemistry and Physics Discussions 11, n. 9 (22 settembre 2011): 26347–413. http://dx.doi.org/10.5194/acpd-11-26347-2011.
Testo completoAbstract (sommario):
Abstract. Recent experimental findings indicate that Secondary Organic Aerosol (SOA) represents an important and, under many circumstances, the major fraction of the organic aerosol burden. Here, we use a global 3-d model (IMPACT) to test the results of different mechanisms for the production of SOA. The basic mechanism includes SOA formation from organic nitrates and peroxides produced from an explicit chemical formulation, using partition coefficients based on thermodynamic principles. We also include the formation of non-evaporative SOA from the reaction of glyoxal and methylglyoxal on aqueous aerosols and cloud droplets as well as from the reaction of epoxides on aqueous aerosols. A model simulation including these SOA formation mechanisms gives an annual global SOA production of 113.5 Tg. The global production of SOA is substantially decreased to 85.0 Tg yr−1 if the HOx regeneration mechanism proposed by Peeters et al. (2009) is used. Model predictions with and without this HOx regeneration scheme are compared with multiple surface observation datasets, namely: the Interagency Monitoring of Protected Visual Environments (IMPROVE) for the United States, the European Monitoring and Evaluation Programme (EMEP) as well as Aerosol Mass Spectrometry (AMS) data measured in both Northern Hemisphere and tropical forest regions. All model simulations realistically predict the organic carbon mass observed in the Northern Hemisphere, although they tend to overestimate the concentrations in tropical forest regions. This overestimate may result from an unrealistically high uptake rate of glyoxal and methylglyoxal on aqueous aerosols and in cloud drops. The modeled OC in the free troposphere is in agreement with measurements in the ITCT-2K4 aircraft campaign over the North America and in pollution layers in Asia during the INTEX-B campaign, although the model underestimates OC in the free troposphere during the ACE-Asia campaign off the coast of Japan.
30
Bharali, Chandrakala, Mary Barth, Rajesh Kumar, Sachin D. Ghude, Vinayak Sinha e Baerbel Sinha. "Role of atmospheric aerosols in severe winter fog over the Indo-Gangetic Plain of India: a case study". Atmospheric Chemistry and Physics 24, n. 11 (6 giugno 2024): 6635–62. http://dx.doi.org/10.5194/acp-24-6635-2024.
Testo completoAbstract (sommario):
Abstract. Winter fog and severe aerosol loading in the boundary layer over northern India, particularly in the Indo-Gangetic Plain (IGP), disrupt the daily lives of millions of people in the region. To better understand the role of aerosol–radiation (AR) feedback on the occurrence, spatial extent, and persistence of winter fog, as well as the associated aqueous chemistry in fog in the IGP, several model simulations have been performed using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). While WRF-Chem was able to represent the fog formation for the 23–24 December 2017 fog event over the central IGP in comparison to station and satellite observations, the model underestimated PM2.5 concentrations compared to the Central Pollution Control Board (CPCB) of India monitoring network. While evaluating aerosol composition for fog events in the IGP, we found that the WRF-Chem aerosol composition was quite different from measurements obtained during the Winter Fog Experiment (WiFEX) in Delhi, with secondary aerosols, particularly the chloride aerosol fraction, being strongly underpredicted (∼ 66.6 %). Missing emission sources (e.g., industry and residential burning of cow dung and trash) and aerosol and chemistry processes need to be investigated to improve model–observation agreement. By investigating a fog event on 23–24 December 2017 over the central IGP, we found that the aerosol–radiation feedback weakens turbulence, lowers the boundary layer height, and increases PM2.5 concentrations and relative humidity (RH) within the boundary layer. Factors affecting the feedback include loss of aerosols through deposition of cloud droplets and internal mixing of absorbing and scattering aerosols. Aqueous-phase chemistry increases the PM2.5 concentrations, which subsequently affect the aerosol–radiation feedback by both increased mass concentrations and aerosol sizes. With aerosol–radiation interaction and aqueous-phase chemistry, fog formation began 1–2 h earlier and caused a longer fog duration than when these processes were not included in the WRF-Chem simulation. The increase in RH in both experiments was found to be important for fog formation as it promoted the growth of aerosol size through water uptake, increasing the fog water content over the IGP. The results from this study suggest that the aerosol–radiation feedback and secondary aerosol formation play an important role in the air quality and the intensity and lifetime of fog over the IGP, yet other feedbacks, such as aerosol–cloud interactions, need to be quantified.
31
Lim, Y. B., Y. Tan, M. J. Perri, S. P. Seitzinger e B. J. Turpin. "Aqueous chemistry and its role in secondary organic aerosol (SOA) formation". Atmospheric Chemistry and Physics 10, n. 21 (10 novembre 2010): 10521–39. http://dx.doi.org/10.5194/acp-10-10521-2010.
Testo completoAbstract (sommario):
Abstract. There is a growing understanding that secondary organic aerosol (SOA) can form through reactions in atmospheric waters (i.e., clouds, fogs, and aerosol water). In clouds and wet aerosols, water-soluble organic products of gas-phase photochemistry dissolve into the aqueous phase where they can react further (e.g., with OH radicals) to form low volatility products that are largely retained in the particle phase. Organic acids, oligomers and other products form via radical and non-radical reactions, including hemiacetal formation during droplet evaporation, acid/base catalysis, and reaction of organics with other constituents (e.g., NH4+). This paper provides an overview of SOA formation through aqueous chemistry, including atmospheric evidence for this process and a review of radical and non-radical chemistry, using glyoxal as a model precursor. Previously unreported analyses and new kinetic modeling are reported herein to support the discussion of radical chemistry. Results suggest that reactions with OH radicals tend to be faster and form more SOA than non-radical reactions. In clouds these reactions yield organic acids, whereas in wet aerosols they yield large multifunctional humic-like substances formed via radical-radical reactions and their O/C ratios are near 1.
32
Skogerboe, R. K., e S. J. Freeland. "Effects of Solution Composition on the Physical Characteristics of Aerosols Produced by Nebulization". Applied Spectroscopy 39, n. 6 (novembre 1985): 925–30. http://dx.doi.org/10.1366/0003702854249637.
Testo completoAbstract (sommario):
It has been confirmed that the size distribution of the analyte contained in an aqueous aerosol is affected by the chemical composition of the solution nebulized. The present work has shown that the addition of sodium to copper solutions shifts the aerodynamic and physical size distributions for the copper upward, while the sodium size distributions remain relatively constant. Examination of solid aerosols produced by flash evaporation of aqueous droplets has indicated that the particles tend to be hollow spheres which may encapsulate smaller spheres, as has been observed for particles emitted from combustion sources. The possible significance of droplet evaporation during aerosol transport is examined and judged to be a plausible and at least partial cause of the effects observed.
33
Liggio, J., e S. M. Li. "A new source of oxygenated organic aerosol and oligomers". Atmospheric Chemistry and Physics 13, n. 6 (15 marzo 2013): 2989–3002. http://dx.doi.org/10.5194/acp-13-2989-2013.
Testo completoAbstract (sommario):
Abstract. A large oxygenated organic uptake to aerosols was observed when exposing ambient urban air to inorganic acidic and non-acidic sulfate seed aerosol. For non-acidic seed aerosol the uptake was attributed to the direct dissolution of primary vehicle exhaust gases into the aqueous aerosol fraction, and was correlated to the initial seed sulphate mass. The uptake of primary oxygenated organic gases to aerosols in this study represents a significant amount of organic aerosol (OA) that may be considered primary when compared to that reported for primary organic aerosol (POA), but is considerably more oxygenated (O : C ~ 0.3) than traditional POA. Consequently, a fraction of measured ambient oxygenated OA, which correlates with secondary sulphate, may in fact be of a primary, rather than secondary source. These results represent a new source of oxygenated OA on neutral aerosol and imply that the uptake of primary organic gases will occur in the ambient atmosphere, under dilute conditions, and in the presence of pre-existing SO4 aerosols which contain water. Conversely, under acidic seed aerosol conditions, oligomer formation was observed with the uptake of organics being enhanced by a factor of three or more compared to neutral aerosols, and in less than 2 min, representing an additional source of SOA to the atmosphere. This resulted in a trajectory in Van Krevelen space towards higher O : C (slope ~ −1.5), despite a lack of continual gas-phase oxidation in this closed system. The results demonstrate that high molecular weight species will form on acidic aerosols at the ambient level and mixture of organic gases, but are otherwise unaffected by subsequent aerosol neutralization, and that aerosol acidity will affect the organic O : C via aerosol-phase reactions. These two processes, forming oxygenated POA under neutral conditions and SOA under acidic conditions can contribute to the total ambient OA mass and the evolution of ambient aerosol O : C ratios. This may be important for properly representing organic aerosol O : C ratios in air quality and climate models.
34
Tan, Y., Y. B. Lim, K. E. Altieri, S. P. Seitzinger e B. J. Turpin. "Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal". Atmospheric Chemistry and Physics 12, n. 2 (18 gennaio 2012): 801–13. http://dx.doi.org/10.5194/acp-12-801-2012.
Testo completoAbstract (sommario):
Abstract. Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM–10 mM) was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.
35
Mozurkewich, Michael, e Jack G. Calvert. "Reaction probability of N2O5on aqueous aerosols". Journal of Geophysical Research 93, n. D12 (1988): 15889. http://dx.doi.org/10.1029/jd093id12p15889.
Testo completo
36
WOOLMAN, P. S., C. T. COUTTS, D. R. MOLE, P. P. DENDY e T. W. HIGENBOTTAM. "Sites of deposition of aqueous aerosols". Nuclear Medicine Communications 10, n. 3 (marzo 1989): 171–80. http://dx.doi.org/10.1097/00006231-198903000-00009.
Testo completo
37
Clegg, S. L., e P. Brimblecombe. "Chemical modelling of aqueous atmospheric aerosols". Journal of Aerosol Science 23 (gennaio 1992): 893–96. http://dx.doi.org/10.1016/0021-8502(92)90555-a.
Testo completo
38
Tritscher, T., A. P. Praplan, P. F. DeCarlo, B. Temime-Roussel, E. Quivet, N. Marchand, J. Dommen, U. Baltensperger e A. Monod. "Aqueous phase processing of secondary organic aerosols". Atmospheric Chemistry and Physics Discussions 11, n. 7 (28 luglio 2011): 21489–532. http://dx.doi.org/10.5194/acpd-11-21489-2011.
Testo completoAbstract (sommario):
Abstract. The aging of secondary organic aerosol (SOA) by photooxidation in the aqueous phase was experimentally investigated. To simulate multiphase processes, the following experiments were sequentially performed in a smog chamber and in an aqueous phase photoreactor: (1) Gas-phase photooxidation of three different volatile organic compounds (VOC): isoprene, α-pinene, and 1,3,5-trimethylbenzene (TMB) in the presence of NOx, leading to the formation of SOA which was subjected to on-line physical and chemical analysis; (2) particle-to-liquid transfer of water soluble species of SOA using filter sampling and aqueous extraction; (3) aqueous-phase photooxidation of the obtained water extracts; and (4) nebulization of the solutions for a repetition of the on-line characterization. SOA concentrations in the chamber measured with a scanning mobility particle sizer (SMPS) were higher than 200 μg m−3, as the experiments were conducted under high initial concentrations of volatile organic compounds (VOC) and NOx. The aging of SOA through aqueous phase processing was investigated by measuring the physical and chemical properties of the particles online before and after processing using a high resolution time-of-flight aerosol mass spectrometer (AMS) and a hygroscopicity tandem differential mobility analyzer (H-TDMA). It was shown that, after aqueous phase processing, the particles were significantly more hygroscopic, and contained more fragmentation ions at m/z = 44 and less ions at m/z = 43, thus showing a significant impact on SOA aging for the three different precursors. Additionally, the particles were analyzed with a thermal desorption atmospheric pressure ionization aerosol mass spectrometer (TD-API-AMS). Comparing the smog chamber SOA composition and non processed nebulized aqueous extracts with this technique revealed that sampling, extraction and/or nebulization did not significantly impact the chemical composition of SOA formed from isoprene and α-pinene, whereas it affected that formed from TMB. For the two first precursors, the aqueous phase chemical composition of SOA was further investigated using offline measurements, i.e. ion chromatography coupled to a mass spectrometer (IC-MS) and an atmospheric pressure chemical ionization mass spectrometer (APCI-MS) equipped with high pressure liquid chromatography (HPLC-MS). These analyses showed that aqueous phase processing enhanced the formation of some compounds already present in the SOA, thus confirming the aging effect of aqueous phase processes. For isoprene experiments, additional new compounds, likely oligomers, were formed through aqueous phase photooxidation, and their possible origins are discussed.
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Qin, Chao, Yafeng Gou, Yuhang Wang, Yuhao Mao, Hong Liao, Qin'geng Wang e Mingjie Xie. "Gas–particle partitioning of polyol tracers at a suburban site in Nanjing, east China: increased partitioning to the particle phase". Atmospheric Chemistry and Physics 21, n. 15 (13 agosto 2021): 12141–53. http://dx.doi.org/10.5194/acp-21-12141-2021.
Testo completoAbstract (sommario):
Abstract. Gas–particle partitioning of water-soluble organic compounds plays a significant role in influencing the formation, transport, and lifetime of organic aerosols in the atmosphere, but is poorly characterized. In this work, gas- and particle-phase concentrations of isoprene oxidation products (C5-alkene triols and 2-methylterols), levoglucosan, and sugar polyols were measured simultaneously at a suburban site of the western Yangtze River Delta in east China. All target polyols were primarily distributed into the particle phase (85.9 %–99.8 %). Given the uncertainties in measurements and vapor pressure predictions, a dependence of particle-phase fractions on vapor pressures cannot be determined. To explore the impact of aerosol liquid water on gas–particle partitioning of polyol tracers, three partitioning schemes (Cases 1–3) were proposed based on equilibriums of gas vs. organic and aqueous phases in aerosols. If particulate organic matter (OM) is presumed as the only absorbing phase (Case 1), the measurement-based absorptive partitioning coefficients (Kp,OMm) of isoprene oxidation products and levoglucosan were more than 10 times greater than predicted values (Kp,OMt). The agreement between Kp,OMm and Kp,OMt was substantially improved when solubility in a separate aqueous phase was included, whenever water-soluble and water-insoluble OM partitioned into separate (Case 2) or single (Case 3) liquid phases, suggesting that the partitioning of polyol tracers into the aqueous phase in aerosols should not be ignored. The measurement-based effective Henry's law coefficients (KH,em) of polyol tracers were orders of magnitude higher than their predicted values in pure water (KH,wt). Due to the moderate correlations between log(KH,em/KH,wt) and molality of sulfate ions, the gap between KH,em and KH,wt of polyol tracers could not be fully parameterized by the equation defining “salting-in” effects and might be ascribed to mechanisms of reactive uptake, aqueous phase reaction, “like-dissolves-like” principle, etc. These study results also partly reveal the discrepancy between observation and modeling of organic aerosols.
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Hao, Shangpeng, Chao Sun, Yuanpeng Zhang, Haitao Wang, Wenbo Zhao, Xiaolu Wang e Jinghai Li. "Adsorption of Gas-Phase Cyclohexanone on Atmospheric Water Films". Atmosphere 12, n. 12 (20 dicembre 2021): 1705. http://dx.doi.org/10.3390/atmos12121705.
Testo completoAbstract (sommario):
The fate of atmospheric volatile organic compounds (VOCs) strongly depends on the partitioning processes on the surface of aerosols, which are coated with a thin water film. However, the behavior of VOCs in the aqueous film of aerosols is difficult to measure. In this work, the interfacial partition constant of cyclohexanone was determined using a novel flow-tube reactor. A thin, aqueous film placed in the reactor was exposed to cyclohexanone gas. The subsequent partitioning was measured using chromatography techniques. The quality control tests were first conducted to ensure the accuracy of the adsorption experiments. The cyclohexanone concentration was then plotted as a function of film thickness to obtain the partitioning constants. As the thickness of the water film decreased, the aqueous concentration of cyclohexanone increased, indicating that surface adsorption played a dominant role in the uptake of cyclohexanone. According to the temperature dependence of the interfacial partition constant, the solvation enthalpy and entropy of cyclohexanone were obtained. The results of this study would help to elucidate the effect of atmospheric water film on the gas–aerosol partitioning of VOCs, and thus can help to better understand the fate of VOCs in the atmosphere.
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Sun, Yele, Wei Du, Pingqing Fu, Qingqing Wang, Jie Li, Xinlei Ge, Qi Zhang et al. "Primary and secondary aerosols in Beijing in winter: sources, variations and processes". Atmospheric Chemistry and Physics 16, n. 13 (11 luglio 2016): 8309–29. http://dx.doi.org/10.5194/acp-16-8309-2016.
Testo completoAbstract (sommario):
Abstract. Winter has the worst air pollution of the year in the megacity of Beijing. Despite extensive winter studies in recent years, our knowledge of the sources, formation mechanisms and evolution of aerosol particles is not complete. Here we have a comprehensive characterization of the sources, variations and processes of submicron aerosols that were measured by an Aerodyne high-resolution aerosol mass spectrometer from 17 December 2013 to 17 January 2014 along with offline filter analysis by gas chromatography/mass spectrometry. Our results suggest that submicron aerosols composition was generally similar across the winter of different years and was mainly composed of organics (60 %), sulfate (15 %) and nitrate (11 %). Positive matrix factorization of high- and unit-mass resolution spectra identified four primary organic aerosol (POA) factors from traffic, cooking, biomass burning (BBOA) and coal combustion (CCOA) emissions as well as two secondary OA (SOA) factors. POA dominated OA, on average accounting for 56 %, with CCOA being the largest contributor (20 %). Both CCOA and BBOA showed distinct polycyclic aromatic hydrocarbons (PAHs) spectral signatures, indicating that PAHs in winter were mainly from coal combustion (66 %) and biomass burning emissions (18 %). BBOA was highly correlated with levoglucosan, a tracer compound for biomass burning (r2 = 0.93), and made a considerable contribution to OA in winter (9 %). An aqueous-phase-processed SOA (aq-OOA) that was strongly correlated with particle liquid water content, sulfate and S-containing ions (e.g. CH2SO2+) was identified. On average aq-OOA contributed 12 % to the total OA and played a dominant role in increasing oxidation degrees of OA at high RH levels (> 50 %). Our results illustrate that aqueous-phase processing can enhance SOA production and oxidation states of OA as well in winter. Further episode analyses highlighted the significant impacts of meteorological parameters on aerosol composition, size distributions, oxidation states of OA and evolutionary processes of secondary aerosols.
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Волков, Р. С., С. В. Чванов e Д. Д. Андриянов. "Диагностика наличия твердых частиц в каплях водяного аэрозоля по их интерференционной картине". Письма в журнал технической физики 45, n. 12 (2019): 22. http://dx.doi.org/10.21883/pjtf.2019.12.47913.17762.
Testo completoAbstract (sommario):
AbstractWe have experimentally studied the influence of solid impurity particles present in aqueous aerosol droplets on their interference patterns. The interference patterns were studied with the aid of a Nd:YAG laser and CCD video camera. The radii of droplets in the aqueous aerosol ranged within 10–140 μm. Solid particles of four materials were introduced in the aerosol to a mass concentration of 0.003–1 g/L. Specific types of interference patterns determined by the presence of solid impurities in droplets are described, and the influence of impurity type and concentration on the integral characteristics of these patterns (number and type of images) is established. A new approach to determining the impurity concentration and particle dimensions in aerosols is proposed based on the analysis of their interference patterns.
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Dang, Caroline, Michal Segal-Rozenhaimer, Haochi Che, Lu Zhang, Paola Formenti, Jonathan Taylor, Amie Dobracki et al. "Biomass burning and marine aerosol processing over the southeast Atlantic Ocean: a TEM single-particle analysis". Atmospheric Chemistry and Physics 22, n. 14 (21 luglio 2022): 9389–412. http://dx.doi.org/10.5194/acp-22-9389-2022.
Testo completoAbstract (sommario):
Abstract. This study characterizes single-particle aerosol composition from filters collected during the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) and CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) campaigns. In particular the study describes aged biomass burning aerosol (BBA), its interaction with the marine boundary layer and the influence of biomass burning (BB) air on marine aerosol. The study finds evidence of BBA influenced by marine boundary layer processing as well as sea salt influenced by BB air. Secondary chloride aerosols were observed in clean marine air as well as in BB-influenced air in the free troposphere. Higher-volatility organic aerosol appears to be associated with increased age of biomass burning plumes, and photolysis or oxidation may be a mechanism for the apparent increased volatility. Aqueous processing and interaction with the marine boundary layer air may be a mechanism for the presence of sodium on many aged potassium salts. By number, biomass burning potassium salts and modified sea salts are the most observed particles on filter samples. The most commonly observed BC coatings are inorganic salts. These results suggest that atmospheric processes such as photolysis, oxidation and cloud processing are key drivers in the elemental composition and morphology of aged BBA. Fresh BBA inorganic salt content, as it has an important role in the particles' ability to uptake water, may be a key driver in how aqueous processing and atmospheric aging proceed.
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Zhang, Yunjiang, Lili Tang, Philip L. Croteau, Olivier Favez, Yele Sun, Manjula R. Canagaratna, Zhuang Wang et al. "Field characterization of the PM<sub>2.5</sub> Aerosol Chemical Speciation Monitor: insights into the composition, sources, and processes of fine particles in eastern China". Atmospheric Chemistry and Physics 17, n. 23 (6 dicembre 2017): 14501–17. http://dx.doi.org/10.5194/acp-17-14501-2017.
Testo completoAbstract (sommario):
Abstract. A PM2.5-capable aerosol chemical speciation monitor (Q-ACSM) was deployed in urban Nanjing, China, for the first time to measure in situ non-refractory fine particle (NR-PM2.5) composition from 20 October to 19 November 2015, along with parallel measurements of submicron aerosol (PM1) species by a standard Q-ACSM. Our results show that the NR-PM2.5 species (organics, sulfate, nitrate, and ammonium) measured by the PM2.5-Q-ACSM are highly correlated (r2 > 0.9) with those measured by a Sunset Lab OC / EC analyzer and a Monitor for AeRosols and GAses (MARGA). The comparisons between the two Q-ACSMs illustrated similar temporal variations in all NR species between PM1 and PM2.5, yet substantial mass fractions of aerosol species were observed in the size range of 1–2.5 µm. On average, NR-PM1−2.5 contributed 53 % of the total NR-PM2.5, with sulfate and secondary organic aerosols (SOAs) being the two largest contributors (26 and 27 %, respectively). Positive matrix factorization of organic aerosol showed similar temporal variations in both primary and secondary OAs between PM1 and PM2.5, although the mass spectra were slightly different due to more thermal decomposition on the capture vaporizer of the PM2.5-Q-ACSM. We observed an enhancement of SOA under high relative humidity conditions, which is associated with simultaneous increases in aerosol pH, gas-phase species (NO2, SO2, and NH3) concentrations and aerosol water content driven by secondary inorganic aerosols. These results likely indicate an enhanced reactive uptake of SOA precursors upon aqueous particles. Therefore, reducing anthropogenic NOx, SO2, and NH3 emissions might not only reduce secondary inorganic aerosols but also the SOA burden during haze episodes in China.
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McNeill, V. F., J. Patterson, G. M. Wolfe e J. A. Thornton. "The effect of varying levels of surfactant on the reactive uptake of N<sub>2</sub>O<sub>5</sub> to aqueous aerosol". Atmospheric Chemistry and Physics 6, n. 6 (22 maggio 2006): 1635–44. http://dx.doi.org/10.5194/acp-6-1635-2006.
Testo completoAbstract (sommario):
Abstract. Recent observations have detected surface active organics in atmospheric aerosols. We have studied the reaction of N2O5 on aqueous natural seawater and NaCl aerosols as a function of sodium dodecyl sulfate (SDS) concentration to test the effect of varying levels of surfactant on gas-aerosol reaction rates. SDS was chosen as a proxy for naturally occurring long chain monocarboxylic acid molecules, such as palmitic or stearic acid, because of its solubility in water and well-characterized surface properties. Experiments were performed using a newly constructed aerosol flow tube coupled to a chemical ionization mass spectrometer for monitoring the gas phase, and a differential mobility analyzer/condensation particle counter for determining aerosol surface area. We find that the presence of ~3.5wt% SDS in the aerosol, which corresponds to a monolayer surface coverage of ~2×1014 molecules cm-2, suppresses the N2O5 reaction probability, γN2O5, by approximately a factor of ten, independent of relative humidity. Consistent with this observation is a similar reduction in the rate of ClNO2 product generation measured simultaneously. However, the product yield remains nearly constant under all conditions. The degree of suppression is strongly dependent on SDS content in the aerosol, with no discernable effect at 0.1wt% SDS, but significant suppression at what we predict to be submonolayer coverages with 0.3–0.6wt% SDS on NaCl and natural seawater aerosols, respectively.
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Schwier, A. N., G. A. Viglione, Z. Li e V. Faye McNeill. "Modeling the surface tension of complex, reactive organic–inorganic mixtures". Atmospheric Chemistry and Physics 13, n. 21 (5 novembre 2013): 10721–32. http://dx.doi.org/10.5194/acp-13-10721-2013.
Testo completoAbstract (sommario):
Abstract. Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic–inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2–6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski–Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic–inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.
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Tan, Y., Y. B. Lim, K. E. Altieri, S. P. Seitzinger e B. J. Turpin. "Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid". Atmospheric Chemistry and Physics Discussions 11, n. 6 (28 giugno 2011): 18319–47. http://dx.doi.org/10.5194/acpd-11-18319-2011.
Testo completoAbstract (sommario):
Abstract. Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid is an important intermediate in aqueous methylglyoxal oxidation and a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. Altieri et al. (2008) proposed that acetic acid was the precursor of oligoesters observed in methylglyoxal oxidation. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid at concentrations relevant to atmospheric waters (20 μM–10 mM) was oxidized by OH radical. Products were analyzed by ion chromatography (IC), electrospray ionization mass spectrometry (ESI-MS), and IC-ESI-MS. The formation of glyoxylic, glycolic, and oxalic acids were observed. In contrast to methylglyoxal oxidation, succinic acid and oligomers were not detected. Using results from these and methylglyoxal + OH radical experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.
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Donahue, N. M., W. Chuang, S. A. Epstein, J. H. Kroll, D. R. Worsnop, A. L. Robinson, P. J. Adams e S. N. Pandis. "Why do organic aerosols exist? Understanding aerosol lifetimes using the two-dimensional volatility basis set". Environmental Chemistry 10, n. 3 (2013): 151. http://dx.doi.org/10.1071/en13022.
Testo completoAbstract (sommario):
Environmental context Fine particles (aerosols) containing organic compounds are central players in two important environmental issues: aerosol-climate effects and human health effects (including mortality). Although organics constitute half or more of the total fine-particle mass, their chemistry is extremely complex; of critical importance is ongoing oxidation chemistry in both the gas phase and the particle phase. Here we present a method for representing that oxidation chemistry when the actual composition of the organics is not known and show that relatively slow oxidant uptake to particles plays a key role in the very existence of organic aerosols. Abstract Organic aerosols play a critical role in atmospheric chemistry, human health and climate. Their behaviour is complex. They consist of thousands of organic molecules in a rich, possibly highly viscous mixture that may or may not be in phase equilibrium with organic vapours. Because the aerosol is a mixture, compounds from all sources interact and thus influence each other. Finally, most ambient organic aerosols are highly oxidised, so the molecules are secondary products formed from primary emissions by oxidation chemistry and possibly non-oxidative association reactions in multiple phases, including gas-phase oxidation, aqueous oxidation, condensed (organic) phase reactions and heterogeneous interactions of all these phases. In spite of this complexity, we can make a strong existential statement about organic aerosol: They exist throughout the troposphere because heterogeneous oxidation by OH radicals is more than an order of magnitude slower than comparable gas-phase oxidation.
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Khalmanov, A. T., e N. Toshkuvatova. "Modern methods for identification of atoms, molecules, and aerosols in various objects". Industrial laboratory. Diagnostics of materials 89, n. 6 (21 giugno 2023): 23–34. http://dx.doi.org/10.26896/1028-6861-2023-89-6-23-34.
Testo completoAbstract (sommario):
The study is aimed at developing highly sensitive methods of laser analytical spectroscopy. The physical mechanisms of forming useful signals (selective ionization signal and cavity ring-down signal) were identified that provided registration of parameters of atomic and aerosol systems in the intensive pulsed laser field. High-sensitive laser methods of laser resonance ionization spectroscopy in vacuum, laser-enhanced ionization spectrometry in flame, and cavity ringdown laser absorption spectroscopy (CRLAS) are used for the determination of ultra-small concentrations of atoms in different phase states of the substance. Samples of aqueous standard solutions and solid metals of s (Li, K, Na, Ca, Cs), p (Al, In), d (Cr, Mn, Fe, Co, Ni, Cu, Ag, Au, Pt, Zn, Hg), f (Yb) elements, aluminum alloys, especially pure solvents, crystals (NH4F, NaF), semi-conductor materials (GaAs, Si) and various aerosols of salts (NaCl, CsCl, NaI, NaF, KCl AgNO3), chemicals, organic dyes, alloys, soils and rocks were studied. The new mechanisms of getting free particles are revealed and new methods increasing the efficiency of atomization, selective ionization and excitation of atoms in systems «flame», «rod – flame», in atomizer «graphite – furnace» are proposed. The particle size distribution of aerosols formed under the impact of high-power laser radiation on the surface of a solid sample has been studied. The dependence of the absolute concentration of aerosol particles on their size has been determined. Aerosol extinction coefficients and extinction efficiency have been measured using intracavity laser spectroscopy. For the first time new parameters of aerosols are revealed by physical and chemical properties of aerosol plumes from solid surfaces and aerosols of salt of metals and organic aerosols. Methods of additives and calibration curve were used to examine the effects of the matrix on the analytical signal of the studied atoms.
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Pavuluri, C. M., K. Kawamura, N. Mihalopoulos e T. Swaminathan. "Laboratory photochemical processing of aqueous aerosols: formation and degradation of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls". Atmospheric Chemistry and Physics Discussions 15, n. 1 (15 gennaio 2015): 1193–224. http://dx.doi.org/10.5194/acpd-15-1193-2015.
Testo completoAbstract (sommario):
Abstract. To better understand the photochemical processing of dicarboxylic acids and related polar compounds, we conducted batch UV irradiation experiments on two types of aerosol samples collected from India, which represent anthropogenic (AA) and biogenic aerosols (BA), for time periods of 0.5 to 120 h. The irradiated samples were analyzed for molecular compositions of diacids, oxoacids and α-dicarbonyls. The results show that photochemical degradation of oxalic (C2) and malonic (C3) and other C8-C12 diacids overwhelmed their production in aqueous aerosols whereas succinic acid (C4) and C5-C7 diacids showed a significant increase (ca. 10 times) during the course of irradiation experiments. The photochemical formation of oxoacids and α-dicarbonyls overwhelmed their degradation during the early stages of experiment, except for ω-oxooctanoic acid (ωC8) that showed a similar pattern to that of C4. We also found a gradual decrease in the relative abundance of C2 to total diacids and an increase in the relative abundance of C4 during prolonged experiment. Based on the changes in concentrations and mass ratios of selected species with the irradiation time, we hypothesize that iron-catalyzed photolysis of C2 and C3 diacids dominates their concentrations in Fe-rich atmospheric waters, whereas photochemical formation of C4 diacid (via ωC8) is enhanced with photochemical processing of aqueous aerosols in the atmosphere. This study demonstrates that the ambient aerosols contain abundant precursors that produce diacids, oxoacids and α-dicarbonyls, although some species such as oxalic acid decompose extensively during an early stage of photochemical processing.