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 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).

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 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 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 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 Modelling Atmospheric Mineral Aerosol Chemistry to Predict Heterogeneous Photooxidation of SO<sub>2</sub>

2017 ◽  
Author(s):  
Zechen Yu ◽  
Myoseon Jang ◽  
Jiyeon Park
Keyword(s):  
Mineral Dust ◽  
Uv Light ◽  
Full Range ◽  
Saharan Dust ◽  
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 adsorption-desorption kinetics (gas-particle partitioning) of SO2 and NOx. The reaction of adsorbed 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 70 % of total sulfate (60 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 significantly suppressed by the competition between NO2 and SO2 that both consume the dust-surface oxidants (OH radicals or ozone). The AMAR model, derived in this study with ATD particles, will provide a platform for predicting sulfate formation in the presence of authentic dust particles (e.g. Gobi and Saharan dust).

scholarly journals Air quality modelling in the summer over the eastern Mediterranean using WRF-Chem: chemistry and aerosol mechanism intercomparison

2018 ◽  
Vol 18 (3) ◽  
pp. 1555-1571 ◽  
Author(s):  
George K. Georgiou ◽  
Theodoros Christoudias ◽  
Yiannis Proestos ◽  
Jonilda Kushta ◽  
Panos Hadjinicolaou ◽  
...  
Keyword(s):  
Air Quality ◽  
Gas Phase ◽  
Eastern Mediterranean ◽  
Fine Particulate Matter ◽  
Correlation Coefficients ◽  
Photochemical Activity ◽  
Global Model ◽  
So2 Oxidation ◽  
Diurnal Variability ◽  
Ozone Concentrations

Abstract. We employ the WRF-Chem model to study summertime air pollution, the intense photochemical activity and their impact on air quality over the eastern Mediterranean. We utilize three nested domains with horizontal resolutions of 80, 16 and 4 km, with the finest grid focusing on the island of Cyprus, where the CYPHEX campaign took place in July 2014. Anthropogenic emissions are based on the EDGAR HTAP global emission inventory, while dust and biogenic emissions are calculated online. Three simulations utilizing the CBMZ-MOSAIC, MOZART-MOSAIC, and RADM2-MADE/SORGAM gas-phase and aerosol mechanisms are performed. The results are compared with measurements from a dense observational network of 14 ground stations in Cyprus. The model simulates T2 m, Psurf, and WD10 m accurately, with minor differences in WS10 m between model and observations at coastal and mountainous stations attributed to limitations in the representation of the complex topography in the model. It is shown that the south-eastern part of Cyprus is mostly affected by emissions from within the island, under the dominant (60 %) westerly flow during summertime. Clean maritime air from the Mediterranean can reduce concentrations of local air pollutants over the region during westerlies. Ozone concentrations are overestimated by all three mechanisms (9 % ≤ NMB ≤ 23 %) with the smaller mean bias (4.25 ppbV) obtained by the RADM2-MADE/SORGAM mechanism. Differences in ozone concentrations can be attributed to the VOC treatment by the three mechanisms. The diurnal variability of pollution and ozone precursors is not captured (hourly correlation coefficients for O3 ≤ 0.29). This might be attributed to the underestimation of NOx concentrations by local emissions by up to 50 %. For the fine particulate matter (PM2.5), the lowest mean bias (9 µg m−3) is obtained with the RADM2-MADE/SORGAM mechanism, with overestimates in sulfate and ammonium aerosols. Overestimation of sulfate aerosols by this mechanism may be linked to the SO2 oxidation in clouds. The MOSAIC aerosol mechanism overestimates PM2.5 concentrations by up to 22 µg m−3 due to a more pronounced dust component compared to the other two mechanisms, mostly influenced by the dust inflow from the global model. We conclude that all three mechanisms are very sensitive to boundary conditions from the global model for both gas-phase and aerosol pollutants, in particular dust and ozone.

scholarly journals Exploring the chemical fate of the sulfate radical anion by reaction with sulfur dioxide in the gas phase

2014 ◽  
Vol 14 (9) ◽  
pp. 12863-12886
Author(s):  
N. T. Tsona ◽  
N. Bork ◽  
H. Vehkamäki
Keyword(s):  
Relative Humidity ◽  
Gas Phase ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Phase Reaction ◽  
So2 Oxidation ◽  
Gas Phase Reaction ◽  
Cluster Ion ◽  
Anionic Cluster ◽  
Sulfate Radical Anion

Abstract. The gas phase reaction between SO4−(H2O)n and SO2, n = 0–2, is investigated using ab initio calculations and kinetic modeling. Structures of reactants, transition states and products are reported. Our calculations predict that the SO2SO4−(H2O)n cluster ion, formed upon SO2 and SO4−(H2O)n collision, can isomerize to SO3SO3−(H2O)n. The overall reaction is SO2 oxidation by the SO4−(H2O)n anionic cluster. The results show that SO4−(H2O)n is a good SO2 oxidant, especially at low relative humidity, with a~reaction rate constant up to 1.1 × 10−10 cm3 molecule−1 s−1. At high relative humidity, instead, the re-evaporation of SO2 from the SO2SO4−(H2O)n cluster ion is favoured.

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