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 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 An isotope view on ionising radiation as a source of sulphuric acid

2012 ◽  
Vol 12 (2) ◽  
pp. 5039-5064 ◽  
Author(s):  
M. B. Enghoff ◽  
N. Bork ◽  
S. Hattori ◽  
C. Meusinger ◽  
M. Nakagawa ◽  
...  
Keyword(s):  
Gas Phase ◽  
Sulphuric Acid ◽  
Gamma Rays ◽  
Uv Light ◽  
Isotope Ratio Mass Spectrometry ◽  
Ionising Radiation ◽  
Oh Radicals ◽  
Phase Oxidation ◽  
Gas Phase Oxidation ◽  
Mass Dependent

Abstract. Sulphuric acid is an important factor in aerosol nucleation and growth. It has been shown that ions enhance the formation of sulphuric acid aerosols, but the exact mechanism has remained undetermined. Furthermore some studies have found a deficiency in the sulphuric acid budget, suggesting a missing source. In this study the production of sulphuric acid from SO2 through a number of different pathways is investigated. The production methods are standard gas phase oxidation by OH radicals produced by ozone photolysis with UV light, liquid phase oxidation by ozone, and gas phase oxidation initiated by gamma rays. The distributions of stable sulphur isotopes in the products and substrate were measured using isotope ratio mass spectrometry. All methods produced sulphate enriched in 34S and we find a δ34S value of 8.7 ± 0.4‰ (1 standard deviation) for the UV-initiated OH reaction. Only UV light (Hg emission at 253.65 nm) produced a clear non-mass-dependent excess of 33S. The pattern of isotopic enrichment produced by gamma rays is similar, but not equal, to that produced by aqueous oxidation of SO2 by ozone. This, combined with the relative yields of the experiments, suggests a mechanism in which ionising radiation may lead to hydrated ion clusters that serve as nanoreactors for S(IV) to S(VI) conversion.

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 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 Contribution of airborne dust particles to HONO sources

2014 ◽  
Vol 14 (4) ◽  
pp. 4827-4839 ◽  
Author(s):  
N. A. Saliba ◽  
S. G. Moussa ◽  
G. El Tayyar
Keyword(s):  
Gas Phase ◽  
Dust Particles ◽  
Oh Radicals ◽  
Sulfate Ion ◽  
Airborne Dust ◽  
Mineral Oxides ◽  
Synergistic Mechanism ◽  
Dust Events ◽  
Mineral Oxide Surfaces ◽  
Hydrolysis Of

Abstract. HONO is a major precursor for OH radicals in early mornings. Its formation has been mainly attributed to the heterogeneous hydrolysis of NO2 on surfaces such as soot, glass, mineral oxides and aerosol surfaces. In particular, dust events which are loaded with mineral oxide aerosols have been associated with higher HONO concentrations in the gas phase. In order to understand the mechanism of reactions related to this process, samples during dusty and non-dusty days were collected between October 2009 and April 2011. Based on HYSPLIT backward trajectories, data were divided between wind trajectories originating from Arabian or African deserts. In this study an increase of HONO levels was observed during dusty days. The increase in the acidic gas concentrations was accompanied by an increase in the PM nitrate and sulfate ion concentrations. During high relative humidity (African dusty days), it is proposed that the mechanism of NO2 hydrolysis predominates whereas during Arabian dusty days, where the air is relatively dry, a synergistic mechanism of adsorption and reaction between NO2 and SO2 on dust particles to produce HONO and sulfate in the particle phase is suggested. This study implies that the NOx reactivity on mineral oxide surfaces leads to a higher mixing level of OH. An increase in the sulfate forming capacity could account for the underestimation of sulfates in aerosols when the reactive uptake of SO2 alone is considered.

scholarly journals A Novel Pathway of Atmospheric Sulfate Formation Through Carbonate Radical

2021 ◽  
Author(s):  
Yangyang Liu ◽  
Yue Deng ◽  
Jiarong Liu ◽  
Xiaozhong Fang ◽  
Tao Wang ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Density Functional ◽  
Mineral Dust ◽  
Field Measurements ◽  
Dust Particles ◽  
Oxidation Reactions ◽  
Carbonate Radical ◽  
Active Intermediate ◽  
Sulfate Formation ◽  
Electron Transfer Processes

Abstract. Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. However, we show here that CO2 is involved in some important photo-oxidation reactions in the atmosphere through the formation of carbonate radicals (CO3∙-). This potentially active intermediate CO3∙- is routinely overlooked in atmospheric chemistry regarding its effect on sulfate formation. Present work demonstrates that SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3∙-. It can be produced through two routes over mineral dust surfaces: i) hydroxyl radical + CO32-; ii) holes (h+) + CO32-. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radical on the model and authentic dust particles, field measurements of sulfate and (bi)carbonate ions within ambient PM, together with density functional theory (DFT) calculations for single electron transfer processes in terms of CO3∙--initiated S(IV) oxidation, a new role of carbonate radical in atmospheric chemistry is elucidated.

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.

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