scholarly journals Multiphase oxidation of SO<sub>2</sub> by NO<sub>2</sub> on CaCO<sub>3</sub> particles

2018 ◽  
Vol 18 (4) ◽  
pp. 2481-2493 ◽  
Author(s):  
Defeng Zhao ◽  
Xiaojuan Song ◽  
Tong Zhu ◽  
Zefeng Zhang ◽  
Yingjun Liu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Gas Mixture ◽  
Ambient Atmosphere ◽  
Uptake Coefficient ◽  
Direct Oxidation ◽  
So2 Oxidation ◽  
Micro Raman Spectroscopy ◽  
Multiphase Reaction ◽  
Sulfate Formation ◽  
Reactive Uptake Coefficient

Abstract. Heterogeneous/multiphase oxidation of SO2 by NO2 on solid or aqueous particles is thought to be a potentially important source of sulfate in the atmosphere, for example, during heavily polluted episodes (haze), but the reaction mechanism and rate are uncertain. In this study, in order to assess the importance of the direct oxidation of SO2 by NO2 we investigated the heterogeneous/multiphase reaction of SO2 with NO2 on individual CaCO3 particles in N2 using Micro-Raman spectroscopy. In the SO2 ∕ NO2 ∕ H2O ∕ N2 gas mixture, the CaCO3 solid particle was first converted to the Ca(NO3)2 droplet by the reaction with NO2 and the deliquescence of Ca(NO3)2, and then NO2 oxidized SO2 in the Ca(NO3)2 droplet forming CaSO4, which appeared as needle-shaped crystals. Sulfate was mainly formed after the complete conversion of CaCO3 to Ca(NO3)2, that is, during the multiphase oxidation of SO2 by NO2. The precipitation of CaSO4 from the droplet solution promoted sulfate formation. The reactive uptake coefficient of SO2 for sulfate formation is on the order of 10−8, and RH enhanced the uptake coefficient. We estimate that the direct multiphase oxidation of SO2 by NO2 is not an important source of sulfate in the ambient atmosphere compared with the SO2 oxidation by OH in the gas phase and is not as important as other aqueous-phase pathways, such as the reactions of SO2 with H2O2, O3, and O2, with or without transition metals.

scholarly journals Multiphase Reaction of SO<sub>2</sub> with NO<sub>2</sub> on CaCO<sub>3</sub> Particles. 1. Oxidation of SO<sub>2</sub> by NO<sub>2</sub>

2017 ◽  
Author(s):  
Defeng Zhao ◽  
Xiaojuan Song ◽  
Tong Zhu ◽  
Zefeng Zhang ◽  
Yingjun Liu
Keyword(s):  
Gas Phase ◽  
Gas Mixture ◽  
Ambient Atmosphere ◽  
Uptake Coefficient ◽  
Direct Oxidation ◽  
So2 Oxidation ◽  
Micro Raman Spectroscopy ◽  
Multiphase Reaction ◽  
Sulfate Formation ◽  
Reactive Uptake Coefficient

Abstract. Heterogeneous/multiphase reaction of SO2 with NO2 on solid or aqueous particles is thought to be a potentially important source of sulfate in the atmosphere, for example, during heavily polluted episodes (haze), but the reaction mechanism and rate are uncertain. In this study, we investigated the heterogeneous/multiphase reaction of SO2 with NO2 on individual CaCO3 particles in N2 using Micro-Raman spectroscopy in order to assess the importance of the direct oxidation of SO2 by NO2. In the SO2/NO2/H2O/N2 gas mixture, the CaCO3 solid particle was first converted to the Ca(NO3)2 droplet by the reaction with NO2 and the deliquescence of Ca(NO3)2, and then NO2 oxidized SO2 in the Ca(NO3)2 droplet forming CaSO4, which appeared as needle-shaped crystals. Sulfate was mainly formed after the complete conversion of CaCO3 to Ca(NO3)2, that is, during the multiphase oxidation of SO2 by NO2. The precipitation of CaSO4 from the droplet solution promoted sulfate formation. The reactive uptake coefficient of SO2 for sulfate formation is on the order of 10−8, and RH enhanced the uptake coefficient. We estimate that the direct multiphase oxidation of SO2 by NO2 is not an important source of sulfate in the ambient atmosphere compared with the SO2 oxidation by OH in the gas phase.

scholarly journals Multiphase Reaction of SO<sub>2</sub> with NO<sub>2</sub> on CaCO<sub>3</sub> Particles. 2. NO<sub>2</sub>-initialized Oxidation of SO<sub>2</sub> by O<sub>2</sub>

2017 ◽  
Author(s):  
Ting Yu ◽  
Defeng Zhao ◽  
Xiaojuan Song ◽  
Tong Zhu
Keyword(s):  
Air Pollution ◽  
Model Simulation ◽  
Ambient Air ◽  
Phase Reaction ◽  
Uptake Coefficient ◽  
Direct Oxidation ◽  
Study Results ◽  
Multiphase Reaction ◽  
Sulfate Formation ◽  
Reactive Uptake Coefficient

Abstract. The reaction of SO2 with NO2 on the surface of aerosol particles has been suggested to be important in sulfate formation during severe air pollution in China. However, we found that the direct oxidation of SO2 by NO2 was slow and might not be the main reason for sulfate formation in ambient air. In this study, we investigated the multiphase reaction of SO2 with NO2 on single CaCO3 particles in synthetic air, i.e., in the presence of O2, using Micro-Raman spectroscopy. The reaction converted the CaCO3 particle to the Ca(NO3)2 droplet containing CaSO4 × 2H2O solid particles embedded in it, which constituted a large fraction of the droplet volume at the end of the reaction. Compared with the reaction in the absence of O2, the morphology of the particle during the reaction in synthetic air was significantly different and the amount of sulfate formed at the end of the experiment was much higher. The reactive uptake coefficient of SO2 for sulfate formation was on the order of 10−5, which was two to three orders of magnitude higher than that in the absence of O2. According to the difference between the reactive uptake coefficient of SO2 in the absence of O2 and that in the presence of O2, we found that in the multiphase reaction of SO2 with NO2 in synthetic air, O2 was the main oxidant of SO2 and necessary for radical chain propagation. NO2 acted as the initializer of the radical formation but not the main oxidant. Such synergy of NO2 and O2 resulted in much faster sulfate formation than when either of them was absent. We estimated that the multiphase oxidation of SO2 by O2 in the presence of NO2 can be an important source of sulfate and sink of SO2 based on the calculated lifetime of SO2 regarding the loss by the multiphase reaction versus the lifetime regarding the loss by the gas phase reaction with OH radical. Parameterizing the reactive uptake coefficient of the reaction observed in our laboratory for further model simulation is needed, as well as an integrated assessment based on field observation, laboratory study results, and model simulation to evaluate the importance of the reaction in ambient air during the severe air pollution period, especially in China.

scholarly journals NO<sub>2</sub>-initiated multiphase oxidation of SO<sub>2</sub> by O<sub>2</sub> on CaCO<sub>3</sub> particles

2018 ◽  
Vol 18 (9) ◽  
pp. 6679-6689 ◽  
Author(s):  
Ting Yu ◽  
Defeng Zhao ◽  
Xiaojuan Song ◽  
Tong Zhu
Keyword(s):  
Air Pollution ◽  
Ambient Air ◽  
Oh Radicals ◽  
Phase Reaction ◽  
Uptake Coefficient ◽  
Multiphase Reaction ◽  
Sulfate Formation ◽  
Reactive Uptake Coefficient ◽  
Air Pollution Episodes ◽  
Pollution Episodes

Abstract. The reaction of SO2 with NO2 on the surface of aerosol particles has been suggested to be important in sulfate formation during severe air pollution episodes in China. However, we found that the direct oxidation of SO2 by NO2 was slow and might not be the main reason for sulfate formation in ambient air. In this study, we investigated the multiphase reaction of SO2 with an O2 ∕ NO2 mixture on single CaCO3 particles using Micro-Raman spectroscopy. The reaction converted the CaCO3 particle to a Ca(NO3)2 droplet, with CaSO4 ⚫ 2H2O solid particles embedded in it, which constituted a significant fraction of the droplet volume at the end of the reaction. The reactive uptake coefficient of SO2 for sulfate formation was on the order of 10−5, which was higher than that for the multiphase reaction of SO2 directly with NO2 by 2–3 orders of magnitude. According to our observations and the literature, we found that in the multiphase reaction of SO2 with the O2 ∕ NO2 mixture, O2 was the main oxidant of SO2 and was necessary for radical chain propagation. NO2 acted as the initiator of radical formation, but not as the main oxidant. The synergy of NO2 and O2 resulted in much faster sulfate formation than the sum of the reaction rates with NO2 and with O2 alone. We estimated that the multiphase oxidation of SO2 by O2 initiated by NO2 could be an important source of sulfate and a sink of SO2, based on the calculated lifetime of SO2 regarding the loss through the multiphase reaction versus the loss through the gas-phase reaction with OH radicals. Parameterization of the reactive uptake coefficient of the reaction observed in our laboratory for further model simulation is needed, as well as an integrated assessment based on field observations, laboratory study results, and model simulations to evaluate the importance of the reaction in ambient air during severe air pollution episodes, especially in China.

scholarly journals Constraining nucleation, condensation, and chemistry in oxidation flow reactors using size-distribution measurements and aerosol microphysical modelling

2018 ◽  
Author(s):  
Anna L. Hodshire ◽  
Brett B. Palm ◽  
M. Lizabeth Alexander ◽  
Qijing Bian ◽  
Pedro Campuzano-Jost ◽  
...  
Keyword(s):  
Size Distribution ◽  
Gas Phase ◽  
Organic Compounds ◽  
Rate Constants ◽  
Accommodation Coefficient ◽  
Uptake Coefficient ◽  
Flow Reactors ◽  
Reactive Uptake Coefficient ◽  
Fragmentation Reactions ◽  
Gas Phase Fragmentation

Abstract. Oxidation flow reactors (OFRs) allow the concentration of a given atmospheric oxidant to be increased beyond ambient levels in order to study secondary organic aerosol (SOA) formation and aging over varying periods of equivalent aging by that oxidant. Previous studies have used these reactors to determine the bulk OA mass and chemical evolution. To our knowledge, no OFR study has focused on the interpretation of the evolving aerosol size distributions. In this study, we use size distribution measurements of the OFR and an aerosol microphysics model to learn about size-dependent processes in the OFR. Specifically, we use OFR exposures between 0.09–0.9 equivalent days of OH aging from the 2011 BEACHON-RoMBAS and the GoAmazon2014/5 field campaigns. We use simulations in the TOMAS (TwO-Moment Aerosol Sectional) microphysics box model to constrain the following parameters in the OFR: (1) the rate constant of gas-phase functionalization reactions of organic compounds with OH, (2) the rate constant of gas-phase fragmentation reactions of organic compounds with OH, (3) the reactive uptake coefficient for heterogeneous fragmentation reactions with OH, (4) the nucleation rate constants for three different nucleation schemes, and (5) an effective accommodation coefficient that accounts for possible particle diffusion limitations of particles larger than 60 nm in diameter. We find the best model-to-measurement agreement when the accommodation coefficient of the larger particles (Dp > 60 nm) was 0.1 or lower (with an accommodation coefficient of 1 for smaller particles), which suggests a diffusion limitation in the larger particles. When using these low accommodation-coefficient values, the model agrees with measurements when using a published H2SO4-organics nucleation mechanism and previously published values of rate constants for gas-phase oxidation reactions. Further, gas-phase fragmentation was found to have a significant impact upon the size distribution, and including fragmentation was necessary for accurately simulating the distributions in the OFR. The model was insensitive to the value of the reactive uptake coefficient on these aging timescales. Monoterpenes and isoprene could explain 24–95 % of the observed change in total volume of aerosol in the OFR, with ambient semivolatile and intermediate-volatility organic compounds (S/IVOCs) appearing to explain the remainder of the change in total volume. These results provide support to the mass-based findings of previous OFR studies, give insight to important size-distribution dynamics in the OFR, and enable the design of future OFR studies focused on new particle formation and/or microphysical processes.

scholarly journals Constraining nucleation, condensation, and chemistry in oxidation flow reactors using size-distribution measurements and aerosol microphysical modeling

2018 ◽  
Vol 18 (16) ◽  
pp. 12433-12460 ◽  
Author(s):  
Anna L. Hodshire ◽  
Brett B. Palm ◽  
M. Lizabeth Alexander ◽  
Qijing Bian ◽  
Pedro Campuzano-Jost ◽  
...  
Keyword(s):  
Size Distribution ◽  
Gas Phase ◽  
Organic Compounds ◽  
Rate Constants ◽  
Accommodation Coefficient ◽  
Uptake Coefficient ◽  
Flow Reactors ◽  
Reactive Uptake Coefficient ◽  
Fragmentation Reactions ◽  
Gas Phase Fragmentation

Abstract. Oxidation flow reactors (OFRs) allow the concentration of a given atmospheric oxidant to be increased beyond ambient levels in order to study secondary organic aerosol (SOA) formation and aging over varying periods of equivalent aging by that oxidant. Previous studies have used these reactors to determine the bulk OA mass and chemical evolution. To our knowledge, no OFR study has focused on the interpretation of the evolving aerosol size distributions. In this study, we use size-distribution measurements of the OFR and an aerosol microphysics model to learn about size-dependent processes in the OFR. Specifically, we use OFR exposures between 0.09 and 0.9 equivalent days of OH aging from the 2011 BEACHON-RoMBAS and GoAmazon2014/5 field campaigns. We use simulations in the TOMAS (TwO-Moment Aerosol Sectional) microphysics box model to constrain the following parameters in the OFR: (1) the rate constant of gas-phase functionalization reactions of organic compounds with OH, (2) the rate constant of gas-phase fragmentation reactions of organic compounds with OH, (3) the reactive uptake coefficient for heterogeneous fragmentation reactions with OH, (4) the nucleation rate constants for three different nucleation schemes, and (5) an effective accommodation coefficient that accounts for possible particle diffusion limitations of particles larger than 60 nm in diameter. We find the best model-to-measurement agreement when the accommodation coefficient of the larger particles (Dp > 60 nm) was 0.1 or lower (with an accommodation coefficient of 1 for smaller particles), which suggests a diffusion limitation in the larger particles. When using these low accommodation-coefficient values, the model agrees with measurements when using a published H2SO4-organics nucleation mechanism and previously published values of rate constants for gas-phase oxidation reactions. Further, gas-phase fragmentation was found to have a significant impact upon the size distribution, and including fragmentation was necessary for accurately simulating the distributions in the OFR. The model was insensitive to the value of the reactive uptake coefficient on these aging timescales. Monoterpenes and isoprene could explain 24 %–95 % of the observed change in total volume of aerosol in the OFR, with ambient semivolatile and intermediate-volatility organic compounds (S/IVOCs) appearing to explain the remainder of the change in total volume. These results provide support to the mass-based findings of previous OFR studies, give insight to important size-distribution dynamics in the OFR, and enable the design of future OFR studies focused on new particle formation and/or microphysical processes.

scholarly journals Modeling atmospheric mineral aerosol chemistry to predict heterogeneous photooxidation of SO<sub>2</sub>

2017 ◽  
Vol 17 (16) ◽  
pp. 10001-10017 ◽  
Author(s):  
Zechen Yu ◽  
Myoseon Jang ◽  
Jiyeon Park
Keyword(s):  
Gas Phase ◽  
Mineral Dust ◽  
Uv Light ◽  
Full Range ◽  
Dust Particles ◽  
Oh Radicals ◽  
Desorption Kinetics ◽  
So2 Oxidation ◽  
Photocatalytic Ability ◽  
Sulfate Formation

Abstract. The photocatalytic ability of airborne mineral dust particles is known to heterogeneously promote SO2 oxidation, but prediction of this phenomenon is not fully taken into account by current models. In this study, the Atmospheric Mineral Aerosol Reaction (AMAR) model was developed to capture the influence of air-suspended mineral dust particles on sulfate formation in various environments. In the model, SO2 oxidation proceeds in three phases including the gas phase, the inorganic-salted aqueous phase (non-dust phase), and the dust phase. Dust chemistry is described as the absorption–desorption kinetics of SO2 and NOx (partitioning between the gas phase and the multilayer coated dust). The reaction of absorbed SO2 on dust particles occurs via two major paths: autoxidation of SO2 in open air and photocatalytic mechanisms under UV light. The kinetic mechanism of autoxidation was first leveraged using controlled indoor chamber data in the presence of Arizona Test Dust (ATD) particles without UV light, and then extended to photochemistry. With UV light, SO2 photooxidation was promoted by surface oxidants (OH radicals) that are generated via the photocatalysis of semiconducting metal oxides (electron–hole theory) of ATD particles. This photocatalytic rate constant was derived from the integration of the combinational product of the dust absorbance spectrum and wave-dependent actinic flux for the full range of wavelengths of the light source. The predicted concentrations of sulfate and nitrate using the AMAR model agreed well with outdoor chamber data that were produced under natural sunlight. For seven consecutive hours of photooxidation of SO2 in an outdoor chamber, dust chemistry at the low NOx level was attributed to 55 % of total sulfate (56 ppb SO2, 290 µg m−3 ATD, and NOx less than 5 ppb). At high NOx ( >  50 ppb of NOx with low hydrocarbons), sulfate formation was also greatly promoted by dust chemistry, but it was suppressed by the competition between NO2 and SO2, which both consume the dust-surface oxidants (OH radicals or ozone).

From O2–-Initiated SO2 Oxidation to Sulfate Formation in the Gas Phase

2018 ◽  
Vol 122 (27) ◽  
pp. 5781-5788 ◽  
Author(s):  
Narcisse T. Tsona ◽  
Junyao Li ◽  
Lin Du
Keyword(s):  
Gas Phase ◽  
So2 Oxidation ◽  
Sulfate Formation

scholarly journals A potential source of atmospheric sulfate from O<sub>2</sub><sup>−</sup>-induced SO<sub>2</sub> oxidation by ozone

2019 ◽  
Vol 19 (1) ◽  
pp. 649-661 ◽  
Author(s):  
Narcisse Tchinda Tsona ◽  
Lin Du
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Low Energy ◽  
Aerosol Formation ◽  
So2 Oxidation ◽  
Title Reaction ◽  
Chemical Fate ◽  
Atmospheric Fate ◽  
Potential Source ◽  
Sulfate Formation

Abstract. It was formerly demonstrated that O2SOO− forms at collisions rate in the gas phase as a result of SO2 reaction with O2-. Here, we present a theoretical investigation of the chemical fate of O2SOO− by reaction with O3 in the gas phase, based on ab initio calculations. Two main mechanisms were found for the title reaction, with fundamentally different products: (i) formation of a van der Waals complex followed by electron transfer and further decomposition to O2 + SO2 + O3- and (ii) formation of a molecular complex from O2 switching by O3, followed by SO2 oxidation to SO3- within the complex. Both reactions are exergonic, but separated by relatively low energy barriers. The products in the former mechanism would likely initiate other SO2 oxidations as shown in previous studies, whereas the latter mechanism closes a path wherein SO2 is oxidized to SO3-. The latter reaction is atmospherically relevant since it forms the SO3- ion, hereby closing the SO2 oxidation path initiated by O2-. The main atmospheric fate of SO3- is nothing but sulfate formation. Exploration of the reactions kinetics indicates that the path of reaction (ii) is highly facilitated by humidity. For this path, we found an overall rate constant of 4.0×10-11 cm3 molecule−1 s−1 at 298 K and 50 % relative humidity. The title reaction provides a new mechanism for sulfate formation from ion-induced SO2 oxidation in the gas phase and highlights the importance of including such a mechanism in modeling sulfate-based aerosol formation rates.

scholarly journals A potential source of atmospheric sulfate from O<sub>2</sub><sup>−</sup>-induced SO<sub>2</sub> oxidation by ozone

2018 ◽  
Author(s):  
Narcisse Tchinda Tsona ◽  
Lin Du
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Low Energy ◽  
Aerosol Formation ◽  
So2 Oxidation ◽  
Title Reaction ◽  
Chemical Fate ◽  
Atmospheric Fate ◽  
Potential Source ◽  
Sulfate Formation

Abstract. It was formerly demonstrated that O2SOO− forms at collisions rate in the gas-phase as a result of SO2 reaction with O2−. Hereby, we present a theoretical investigation of the chemical fate of O2SOO− by reaction with O3 in the gas-phase, based on ab initio calculations. Two main mechanisms were found for the title reaction, with fundamentally different products: (i) formation of a van der Waals complex followed by electron transfer and further decomposition to O2 + SO2 + O3− and (ii) formation of a molecular complex from O2 switching by O3, followed by SO2 oxidation to SO3− within the complex. Both reactions are exergonic, but separated by relatively low energy barriers. The products in the former mechanism would likely initiate other SO2 oxidations as shown in previous studies, whereas the latter mechanism closes a path wherein SO2 is oxidized to SO3−. The latter reaction is atmospherically relevant since it forms the SO3− ion, hereby closing the SO2 oxidation path initiated by O2−. The main atmospheric fate of SO3− is nothing but sulfate formation. Exploration of the reactions kinetics indicates that the path of reaction (ii) is highly facilitated by humidity. For this path, we found an overall rate constant of 4.0 × 10−11 cm3 molecule−1 s−1 at 298 K and 50 % relative humidity. The title reaction provides a new mechanism for sulfate formation from ion-induced SO2 oxidation in the gas-phase and highlights the importance of including such mechanism in modelling sulfate-based aerosol formation rates.

scholarly journals An Atmospheric Origin for HCN-Derived Polymers on Titan

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 965
Author(s):  
Zoé Perrin ◽  
Nathalie Carrasco ◽  
Audrey Chatain ◽  
Lora Jovanovic ◽  
Ludovic Vettier ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Gas Phase ◽  
Formation Process ◽  
Upper Atmosphere ◽  
Gas Mixture ◽  
Space Probe ◽  
Atmospheric Haze ◽  
Formation And Evolution ◽  
Haze Formation

Titan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated the atmospheric haze formation process, experimentally. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze.

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