Développement d’un modèle de chimie multiphase couplé à un modèle de microphysique quasi-spectral... more Développement d’un modèle de chimie multiphase couplé à un modèle de microphysique quasi-spectral: Application à un événement nuageux échantillonné au Puy de Dôme Soutenue publiquement le 8 décembre 2000, devant la commission d’examen
The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied... more The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied from an isoprene/NO x /light system in an atmospheric simulation chamber. It was shown that the presence of a liquid water cloud leads to a faster and higher SOA formation than under dry conditions. When a cloud is generated early in the photooxidation reaction, before any SOA formation has occurred, a fast SOA formation is observed with mass yields ranging from 0.002 to 0.004. These yields are two and four times higher than those observed under dry conditions. When the cloud is generated at a later photooxidation stage, after isoprene SOA is stabilized at its maximum mass concentration, a rapid increase (by a factor of two or higher) of the SOA mass concentration is observed. The SOA chemical composition is influenced by cloud generation: the additional SOA formed during cloud events is composed of both organics and nitrate containing species. This SOA formation can be linked to water soluble volatile organic compounds (VOCs) dissolution in the aqueous phase and to further aqueous phase reactions. Cloud-induced SOA formation is experimentally demonstrated in this study, thus highlighting the importance of aqueous multiphase systems in atmospheric SOA formation estimations.
Submitted for the MAR14 Meeting of The American Physical Society Effects of Aqueous Solvation on ... more Submitted for the MAR14 Meeting of The American Physical Society Effects of Aqueous Solvation on the Photochemistry of Pyruvic Acid ALLISON REED-HARRIS, University of Colorado at Boulder, BARBARA ERVENS, Cooperative Institute for Research in Environmental Sciences (CIRES) / National Oceanic & Atmospheric Administration (NOAA), RICHARD SHOEMAKER, REBECCA RAPF, JAY KROLL, ELIZABETH GRIFFITH, University of Colorado at Boulder, ANNE MONOD, Aix Marseille Universite, VERONICA VAIDA, University of Colorado at Boulder — The role of organic compounds in atmospheric chemistry leading to aerosol formation is under investigation due to the necessity to understand the effects of aerosols on global climate change. It has recently been shown that important pathways in formation of organic aerosols are in aqueous environments where high molecular weight products are formed and can potentially contribute to atmospheric aerosol mass. This presentation describes the photochemistry of pyruvic acid in a...
Ammonium sulfate (AS) particles are widely used for studying the physical-chemistry processes of ... more Ammonium sulfate (AS) particles are widely used for studying the physical-chemistry processes of aerosols and for instrument calibrations. Small quantities of organic matter can greatly influence the studied properties, as observed by many laboratory studies. In this work, monodisperse particles (200-500 nm aerodynamic diameter) were generated by nebulizing various AS solutions and organic impurities were quantified relative to sulfate using a highresolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The organic content found in AS solutions was also tentatively identified using a liquid chromatographytandem mass spectrometer (LC-MS). The results from both analytical techniques were consistent and demonstrated that the organic impurities contained oxygen, nitrogen, and/or sulfur, their molecular masses ranged from m/z 69 to 420, and they likely originate from the commercial AS crystals. For AS particle sizes ranging from 200 to 500 nm, the total mass fraction of organic compounds (relative to sulfate) ranged from 3.8 % to 1.5 %, respectively. An inorganicorganic mixture model suggested that the organic impurities were coated on the AS particle with a surface density of 1.1 × 10 −3 g m −2. A series of tests were performed to remove the organic content (using pure N 2 in the flow, ultrapure water in the solutions, and very high AS quality), showing that at least 40 % of the organic impurities could be removed. In conclusion, it is recommended to use AS seeds with caution, especially when small particles are used, in terms of AS purity and water purity when aqueous solutions are used for atomization.
Nitrogen oxides (NO x = q NO + q NO 2) intensely impact air quality and the environment as they p... more Nitrogen oxides (NO x = q NO + q NO 2) intensely impact air quality and the environment as they play key roles in the production of relevant air pollutants such as ozone (O 3), nitrous acid (HONO), nitric acid (HNO 3), and secondary organic aerosol (SOA). Their atmospheric chemistry controls the concentrations of the three main oxidants, O 3 , q OH, and NO 3 q radicals. The past few decades have witnessed important reductions in NO x direct emissions in Europe or North America, resulting in changes in their atmospheric fate, by
Bulletin of the American Meteorological Society, 2019
The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role o... more The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical propertie...
In this work, the proton transfer reaction between the hydronium ion (H 3 O +) and methyl iodide ... more In this work, the proton transfer reaction between the hydronium ion (H 3 O +) and methyl iodide (CH 3 I) is studied to investigate if consistent quantification of the gas phase CH 3 I is possible in humid air. The neutral CH 3 I molecule was chosen because this compound is of environmental importance in the field of nuclear power plant safety and nuclear energy. Water was used as a reagent ion source in a conventional Insbruck PTR-MS to produce H 3 O + reagent ions. The use of H 3 O + ions allows for fast, sensitive and specific detection of gas phase CH 3 I via a proton-transfer reaction H 3 O + + CH 3 I → [CH 3 I-H] + + H 2 O. The instrument response was linear in the tested 5 to 96 ppbV range and the PTR-MS sensitivity was observed to be humidity dependent. The observed sensitivity was in found to range between 1.6 to 3.3 cps/ppb at relative humidity between 63 and 15% at T= 23 • C. A typical H 3 O + primary ion signal was 10 7 cps and the normalized sensitivity was in the range between 0.16 and 0.33 ncps/ppb. The instrument CH 3 IH + ion background rate was 6.8 ± 1.4 cps and the dwell time was 1 second. The detection limit was calculated as 3 times the standard deviation of the background level and ranged between 1.3 and 3.8 ppb. The theoretical collision rate based on the dipole moment and molecular polarizability is calculated. The theoretical collision rate is compared with the experimentally obtained values. The results indicate that the PTR-MS technique is a good analytical method to detect and quantify gas phase CH 3 I concentrations.
A general presentation of the Earth's atmosphere is provided, with the associated photochemical p... more A general presentation of the Earth's atmosphere is provided, with the associated photochemical processes and oxidizing capacity. The article focuses on the atmospheric reactivity of Volatile Organic Compounds (VOCs) and the associated reaction products in the gas phase (ozone, oxygenated organic compounds, organic nitrates. . .) and in the particle phase, namely, the Secondary Organic Aerosols (SOA). The understanding of the processes leading to SOA formation is currently a "hot topic" because of: i) their high concentrations in the measured total organic matter, and ii) their potential important impacts on health and climate change. The initial theory of SOA formation was based on thermodynamic phase transfers of oxidized reaction products of VOCs, but it failed to explain the presence of high molecular weight (high-MW) compounds observed in SOA as well as a 1 to 2 orders of magnitude discrepancy between models and observations on the quantity of SOA. Therefore, different research investigations have been proposed such as heterogeneous and aqueous phase reactivity of organic compounds.
Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpre... more Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpretation of the Earth's changing energy budget. The present study explores experimentally the impacts of water condensation-evaporation events, mimicking processes occurring in atmospheric clouds, on the molecular composition of secondary organic aerosol (SOA) from the photooxidation of methacrolein. A range of on-and off-line mass spectrometry techniques were used to obtain a detailed chemical characterization of SOA formed in control experiments in dry conditions, in triphasic experiments simulating gas-particle-cloud droplet interactions (starting from dry conditions and from 60% relative humidity (RH)), and in bulk aqueous-phase experiments. We observed that cloud events trigger fast SOA formation accompanied by evaporative losses. These evaporative losses decreased SOA concentration in the simulation chamber by 25−32% upon RH increase, while aqueous SOA was found to be metastable and slowly evaporated after cloud dissipation. In the simulation chamber, SOA composition measured with a high-resolution time-offlight aerosol mass spectrometer, did not change during cloud events compared with high RH conditions (RH > 80%). In all experiments, off-line mass spectrometry techniques emphasize the critical role of 2-methylglyceric acid as a major product of isoprene chemistry, as an important contributor to the total SOA mass (15−20%) and as a key building block of oligomers found in the particulate phase. Interestingly, the comparison between the series of oligomers obtained from experiments performed under different conditions show a markedly different reactivity. In particular, long reaction times at high RH seem to create the conditions for aqueous-phase processing to occur in a more efficient manner than during two relatively short cloud events.
The journal of physical chemistry. A, Jan 17, 2017
Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment c... more Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment consisting of multiple phases and interfacial regions. To explore the effects of such conditions on the reactivity of chemical systems, we employ an environmental simulation chamber to investigate the multiphase photolysis of pyruvic acid, which photoreacts in the troposphere in aqueous particles and in the gas phase. Upon irradiation of nebulized pyruvic acid, acetic acid and carbon dioxide are rapidly generated, which is consistent with previous literature on the bulk phase photolysis reactions. Additionally, we identify a new C6 product, zymonic acid, a species that has not previously been reported from pyruvic acid photolysis under any conditions. Its observation here, and corresponding spectroscopic signatures, indicates it could be formed by heterogeneous reactions at the droplet surface. Prior studies of the aqueous photolysis of pyruvic acid have shown that high-molecular-weight c...
Organic compounds of both anthropogenic and natural origin are ubiquitous in the multiphasic atmo... more Organic compounds of both anthropogenic and natural origin are ubiquitous in the multiphasic atmospheric medium. Their transformation in the atmosphere affects air quality and the global climate. Modelling provides a useful tool to investigate the chemistry of organic compounds in the tropospheric multiphase system. While several comprehensive explicit mechanisms exist in the gas phase, explicit mechanisms are much more limited in the aqueous phase.<br><br> Recently, new empirical methods have been developed to estimate HO<sup>•</sup> reaction rates in the aqueous phase: structure-activity relationships (SARs) provide global rate constants and branching ratios for HO<sup>•</sup> abstraction from and addition to atmospheric organic compounds. Based on these SARs, a new detailed aqueous-phase mechanism, named the cloud explicit physico-chemical scheme (CLEPS), to describe the oxidation of hydrosoluble organic compounds resulting from isoprene oxidat...
... Design of an environmental chamber for the study of atmospheric chemistry : New developments ... more ... Design of an environmental chamber for the study of atmospheric chemistry : New developments in the analytical device. ... Une chambre de simulation atmosphérique a été conçue et réalisée au Laboratoire interuniversitaire des systèmes atmosphériques (Lisa), afin de mener à ...
A multiphase box model for a remote environment of the troposphere has been developed with an exp... more A multiphase box model for a remote environment of the troposphere has been developed with an explicit chemistry for both gas and aqueous phase. The model applied to a set of measurements performed by Voisin et al. (2000) during the European CIME experiment for a cloud event on 13th December 1997 at the top of the Puy de Do(me (France). The results of the simulation are compared to the measurements in order to follow the evolution of the ambient chemical composition as a function of the pH and of the varying water content. After verifying that the model retrieves the main features observed in the behavior of species in the cloud droplets, a detailed analysis of the simulated chemical regime is performed. It essentially discusses the sources and sinks of radical in aqueous phase, the relative importance of the oxidation pathways of volatile organic compounds by the main radicals and the conversion of S(IV) into S(VI) which seems to be in#uenced by the presence of peroxonitric acid, HNO , in aqueous phase in the environmental conditions that are considered with low H O. These numerical results are then compared with the theoretical study from Herrmann et al. (2000), who proposed a slightly di!erent mechanism, including C2 chemistry and transition metal chemistry whereas they neglect some reaction pathways, such as the one involving OHCH O radical. This double confrontation between model results and both real experimental data and numerical results from Herrmann et al. (2000) underlines limitations of such modeling approach that does not include any dynamical or microphysical coupling but also demonstrates its capability to identify the main oxidants or reactants in aqueous phase in real environmental conditions more realistic than a purely theoretical approach. The originality of this study resides in the explicit and exhaustive ways the chemical reactions are treated in aqueous phase and in a "rst attempt to compare such a detailed chemical scheme to real environmental conditions.
Développement d’un modèle de chimie multiphase couplé à un modèle de microphysique quasi-spectral... more Développement d’un modèle de chimie multiphase couplé à un modèle de microphysique quasi-spectral: Application à un événement nuageux échantillonné au Puy de Dôme Soutenue publiquement le 8 décembre 2000, devant la commission d’examen
The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied... more The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied from an isoprene/NO x /light system in an atmospheric simulation chamber. It was shown that the presence of a liquid water cloud leads to a faster and higher SOA formation than under dry conditions. When a cloud is generated early in the photooxidation reaction, before any SOA formation has occurred, a fast SOA formation is observed with mass yields ranging from 0.002 to 0.004. These yields are two and four times higher than those observed under dry conditions. When the cloud is generated at a later photooxidation stage, after isoprene SOA is stabilized at its maximum mass concentration, a rapid increase (by a factor of two or higher) of the SOA mass concentration is observed. The SOA chemical composition is influenced by cloud generation: the additional SOA formed during cloud events is composed of both organics and nitrate containing species. This SOA formation can be linked to water soluble volatile organic compounds (VOCs) dissolution in the aqueous phase and to further aqueous phase reactions. Cloud-induced SOA formation is experimentally demonstrated in this study, thus highlighting the importance of aqueous multiphase systems in atmospheric SOA formation estimations.
Submitted for the MAR14 Meeting of The American Physical Society Effects of Aqueous Solvation on ... more Submitted for the MAR14 Meeting of The American Physical Society Effects of Aqueous Solvation on the Photochemistry of Pyruvic Acid ALLISON REED-HARRIS, University of Colorado at Boulder, BARBARA ERVENS, Cooperative Institute for Research in Environmental Sciences (CIRES) / National Oceanic & Atmospheric Administration (NOAA), RICHARD SHOEMAKER, REBECCA RAPF, JAY KROLL, ELIZABETH GRIFFITH, University of Colorado at Boulder, ANNE MONOD, Aix Marseille Universite, VERONICA VAIDA, University of Colorado at Boulder — The role of organic compounds in atmospheric chemistry leading to aerosol formation is under investigation due to the necessity to understand the effects of aerosols on global climate change. It has recently been shown that important pathways in formation of organic aerosols are in aqueous environments where high molecular weight products are formed and can potentially contribute to atmospheric aerosol mass. This presentation describes the photochemistry of pyruvic acid in a...
Ammonium sulfate (AS) particles are widely used for studying the physical-chemistry processes of ... more Ammonium sulfate (AS) particles are widely used for studying the physical-chemistry processes of aerosols and for instrument calibrations. Small quantities of organic matter can greatly influence the studied properties, as observed by many laboratory studies. In this work, monodisperse particles (200-500 nm aerodynamic diameter) were generated by nebulizing various AS solutions and organic impurities were quantified relative to sulfate using a highresolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The organic content found in AS solutions was also tentatively identified using a liquid chromatographytandem mass spectrometer (LC-MS). The results from both analytical techniques were consistent and demonstrated that the organic impurities contained oxygen, nitrogen, and/or sulfur, their molecular masses ranged from m/z 69 to 420, and they likely originate from the commercial AS crystals. For AS particle sizes ranging from 200 to 500 nm, the total mass fraction of organic compounds (relative to sulfate) ranged from 3.8 % to 1.5 %, respectively. An inorganicorganic mixture model suggested that the organic impurities were coated on the AS particle with a surface density of 1.1 × 10 −3 g m −2. A series of tests were performed to remove the organic content (using pure N 2 in the flow, ultrapure water in the solutions, and very high AS quality), showing that at least 40 % of the organic impurities could be removed. In conclusion, it is recommended to use AS seeds with caution, especially when small particles are used, in terms of AS purity and water purity when aqueous solutions are used for atomization.
Nitrogen oxides (NO x = q NO + q NO 2) intensely impact air quality and the environment as they p... more Nitrogen oxides (NO x = q NO + q NO 2) intensely impact air quality and the environment as they play key roles in the production of relevant air pollutants such as ozone (O 3), nitrous acid (HONO), nitric acid (HNO 3), and secondary organic aerosol (SOA). Their atmospheric chemistry controls the concentrations of the three main oxidants, O 3 , q OH, and NO 3 q radicals. The past few decades have witnessed important reductions in NO x direct emissions in Europe or North America, resulting in changes in their atmospheric fate, by
Bulletin of the American Meteorological Society, 2019
The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role o... more The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical propertie...
In this work, the proton transfer reaction between the hydronium ion (H 3 O +) and methyl iodide ... more In this work, the proton transfer reaction between the hydronium ion (H 3 O +) and methyl iodide (CH 3 I) is studied to investigate if consistent quantification of the gas phase CH 3 I is possible in humid air. The neutral CH 3 I molecule was chosen because this compound is of environmental importance in the field of nuclear power plant safety and nuclear energy. Water was used as a reagent ion source in a conventional Insbruck PTR-MS to produce H 3 O + reagent ions. The use of H 3 O + ions allows for fast, sensitive and specific detection of gas phase CH 3 I via a proton-transfer reaction H 3 O + + CH 3 I → [CH 3 I-H] + + H 2 O. The instrument response was linear in the tested 5 to 96 ppbV range and the PTR-MS sensitivity was observed to be humidity dependent. The observed sensitivity was in found to range between 1.6 to 3.3 cps/ppb at relative humidity between 63 and 15% at T= 23 • C. A typical H 3 O + primary ion signal was 10 7 cps and the normalized sensitivity was in the range between 0.16 and 0.33 ncps/ppb. The instrument CH 3 IH + ion background rate was 6.8 ± 1.4 cps and the dwell time was 1 second. The detection limit was calculated as 3 times the standard deviation of the background level and ranged between 1.3 and 3.8 ppb. The theoretical collision rate based on the dipole moment and molecular polarizability is calculated. The theoretical collision rate is compared with the experimentally obtained values. The results indicate that the PTR-MS technique is a good analytical method to detect and quantify gas phase CH 3 I concentrations.
A general presentation of the Earth's atmosphere is provided, with the associated photochemical p... more A general presentation of the Earth's atmosphere is provided, with the associated photochemical processes and oxidizing capacity. The article focuses on the atmospheric reactivity of Volatile Organic Compounds (VOCs) and the associated reaction products in the gas phase (ozone, oxygenated organic compounds, organic nitrates. . .) and in the particle phase, namely, the Secondary Organic Aerosols (SOA). The understanding of the processes leading to SOA formation is currently a "hot topic" because of: i) their high concentrations in the measured total organic matter, and ii) their potential important impacts on health and climate change. The initial theory of SOA formation was based on thermodynamic phase transfers of oxidized reaction products of VOCs, but it failed to explain the presence of high molecular weight (high-MW) compounds observed in SOA as well as a 1 to 2 orders of magnitude discrepancy between models and observations on the quantity of SOA. Therefore, different research investigations have been proposed such as heterogeneous and aqueous phase reactivity of organic compounds.
Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpre... more Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpretation of the Earth's changing energy budget. The present study explores experimentally the impacts of water condensation-evaporation events, mimicking processes occurring in atmospheric clouds, on the molecular composition of secondary organic aerosol (SOA) from the photooxidation of methacrolein. A range of on-and off-line mass spectrometry techniques were used to obtain a detailed chemical characterization of SOA formed in control experiments in dry conditions, in triphasic experiments simulating gas-particle-cloud droplet interactions (starting from dry conditions and from 60% relative humidity (RH)), and in bulk aqueous-phase experiments. We observed that cloud events trigger fast SOA formation accompanied by evaporative losses. These evaporative losses decreased SOA concentration in the simulation chamber by 25−32% upon RH increase, while aqueous SOA was found to be metastable and slowly evaporated after cloud dissipation. In the simulation chamber, SOA composition measured with a high-resolution time-offlight aerosol mass spectrometer, did not change during cloud events compared with high RH conditions (RH > 80%). In all experiments, off-line mass spectrometry techniques emphasize the critical role of 2-methylglyceric acid as a major product of isoprene chemistry, as an important contributor to the total SOA mass (15−20%) and as a key building block of oligomers found in the particulate phase. Interestingly, the comparison between the series of oligomers obtained from experiments performed under different conditions show a markedly different reactivity. In particular, long reaction times at high RH seem to create the conditions for aqueous-phase processing to occur in a more efficient manner than during two relatively short cloud events.
The journal of physical chemistry. A, Jan 17, 2017
Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment c... more Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment consisting of multiple phases and interfacial regions. To explore the effects of such conditions on the reactivity of chemical systems, we employ an environmental simulation chamber to investigate the multiphase photolysis of pyruvic acid, which photoreacts in the troposphere in aqueous particles and in the gas phase. Upon irradiation of nebulized pyruvic acid, acetic acid and carbon dioxide are rapidly generated, which is consistent with previous literature on the bulk phase photolysis reactions. Additionally, we identify a new C6 product, zymonic acid, a species that has not previously been reported from pyruvic acid photolysis under any conditions. Its observation here, and corresponding spectroscopic signatures, indicates it could be formed by heterogeneous reactions at the droplet surface. Prior studies of the aqueous photolysis of pyruvic acid have shown that high-molecular-weight c...
Organic compounds of both anthropogenic and natural origin are ubiquitous in the multiphasic atmo... more Organic compounds of both anthropogenic and natural origin are ubiquitous in the multiphasic atmospheric medium. Their transformation in the atmosphere affects air quality and the global climate. Modelling provides a useful tool to investigate the chemistry of organic compounds in the tropospheric multiphase system. While several comprehensive explicit mechanisms exist in the gas phase, explicit mechanisms are much more limited in the aqueous phase.<br><br> Recently, new empirical methods have been developed to estimate HO<sup>•</sup> reaction rates in the aqueous phase: structure-activity relationships (SARs) provide global rate constants and branching ratios for HO<sup>•</sup> abstraction from and addition to atmospheric organic compounds. Based on these SARs, a new detailed aqueous-phase mechanism, named the cloud explicit physico-chemical scheme (CLEPS), to describe the oxidation of hydrosoluble organic compounds resulting from isoprene oxidat...
... Design of an environmental chamber for the study of atmospheric chemistry : New developments ... more ... Design of an environmental chamber for the study of atmospheric chemistry : New developments in the analytical device. ... Une chambre de simulation atmosphérique a été conçue et réalisée au Laboratoire interuniversitaire des systèmes atmosphériques (Lisa), afin de mener à ...
A multiphase box model for a remote environment of the troposphere has been developed with an exp... more A multiphase box model for a remote environment of the troposphere has been developed with an explicit chemistry for both gas and aqueous phase. The model applied to a set of measurements performed by Voisin et al. (2000) during the European CIME experiment for a cloud event on 13th December 1997 at the top of the Puy de Do(me (France). The results of the simulation are compared to the measurements in order to follow the evolution of the ambient chemical composition as a function of the pH and of the varying water content. After verifying that the model retrieves the main features observed in the behavior of species in the cloud droplets, a detailed analysis of the simulated chemical regime is performed. It essentially discusses the sources and sinks of radical in aqueous phase, the relative importance of the oxidation pathways of volatile organic compounds by the main radicals and the conversion of S(IV) into S(VI) which seems to be in#uenced by the presence of peroxonitric acid, HNO , in aqueous phase in the environmental conditions that are considered with low H O. These numerical results are then compared with the theoretical study from Herrmann et al. (2000), who proposed a slightly di!erent mechanism, including C2 chemistry and transition metal chemistry whereas they neglect some reaction pathways, such as the one involving OHCH O radical. This double confrontation between model results and both real experimental data and numerical results from Herrmann et al. (2000) underlines limitations of such modeling approach that does not include any dynamical or microphysical coupling but also demonstrates its capability to identify the main oxidants or reactants in aqueous phase in real environmental conditions more realistic than a purely theoretical approach. The originality of this study resides in the explicit and exhaustive ways the chemical reactions are treated in aqueous phase and in a "rst attempt to compare such a detailed chemical scheme to real environmental conditions.
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Papers by Anne Monod