Preprints
https://doi.org/10.5194/acp-2021-788
https://doi.org/10.5194/acp-2021-788

  25 Oct 2021

25 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Contribution of the gas-phase reaction between hydroxyl radical and sulfur dioxide to the sulfate aerosol over West Pacific

Yu-Wen Chen1, Yi-Chun Chen1, Charles C.-K. Chou1, Hui-Ming Hung2, Shih-Yu Chang3, Lisa Eirenschmalz4, Michael Lichtenstern4, Helmut Ziereis4, Hans Schlager4, Greta Stratmann4,a, Katharina Kaiser5,6, Johannes Schneider6, Stephan Borrmann5,6, Florian Obersteiner7, Eric Förster7, Andreas Zahn7, Wei-Nai Chen1, Po-Hsiung Lin2, Shuenn-Chin Chang8, Maria Dolores Andrés Hernández9, Pao-Kuan Wang1, and John P. Burrows9 Yu-Wen Chen et al.
  • 1Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
  • 2Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan
  • 3Department of Public Health, Chung Shan Medical University, Taichung, Taiwan
  • 4Institute of Atmospheric Physics, German Aerospace Center, Wessling, Germany
  • 5Institute for Atmospheric Physics, Johannes Gutenberg-University, Mainz, Germany
  • 6Max Planck Institute for Chemistry, Mainz, Germany
  • 7Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 8Environmental Protection Administration, Taipei, Taiwan
  • 9Institute of Environmental Physics, University Bremen, Bremen, Germany
  • anow at: German Electron Synchrotron, Hamburg, Germany

Abstract. Sulfate is among the major components of atmospheric aerosols or fine particulate matters. Aerosols loaded with sulfate result in low air quality, damage to ecosystems, and influences on climate change. Sulfate aerosols could originate from that directly emitted to the atmosphere and that produced by atmospheric physicochemical processes. The latter is generated from sulfur dioxide (SO2) via oxidation either in the gas phase reactions or in the aqueous phase. Several mechanisms of SO2 oxidation have been proposed, but the differentiation of the various mechanisms and identification of the sources remain challenging. To meet this need, a new method to estimate the contribution of the gas-phase reaction between hydroxyl radical (OH) and SO2 to the sulfate aerosol is proposed and investigated. Briefly, we consider the OH-reaction rates of the respective trace gases that compete for OH radicals with SO2 in the troposphere, and estimate the fraction of SO2-OH reaction in the total OH reactivity. Then the relationship between sulfate concentration and the SO2-OH reaction is analyzed statistically to investigate the sources of sulfate in aerosols. We test this method using the data from ground-based observations and aircraft measurements made during the Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales in Asia (EMeRGe-Asia) over the western Taiwan and West Pacific regions. Our results show that the estimated SO2-OH reactivity fraction is well-correlated with sulfate concentration. The sulfate production from SO2-OH reaction accounts for approximately 30 % of the total sulfate in aerosols collected at the surface and near-surface (altitude < 600 m) in our study area, comparable to the estimates from other model simulations. Within its assumptions and limitations, this new method provides a valuable approach to investigate the significance of SO2-OH reaction regionally and globally.

Yu-Wen Chen et al.

Status: open (until 06 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Yu-Wen Chen et al.

Yu-Wen Chen et al.

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Short summary
By presenting an approach using EMeRGe-Asia airborne field measurements and surface observations, this study shows that the fraction of OH reactivity due to SO2-OH reaction has a significant correlation with the sulfate concentration. Approximately 30 % of sulfate is produced by SO2-OH reaction. Our results underline the importance of SO2-OH gas-phase oxidation in sulfate formation, and demonstrate that the method can be applied to other regions and under different meteorological conditions.
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