Atmospheric Photosensitization: A New Pathway for Sulfate Formation

Abstract

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Supplementary material to "Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds"

“…55 Finally, daytime mean concentrations were calculated for urban winter haze, rural aerosol and rural/urban cloud conditions based on the modelled PS* concentration profiles (see Table 1 in the main manuscript text) and applied for the comparison of the different S(IV) to S(VI) conversion pathways (see Fig 7). The obtained daytime mean concentrations, ranging from about few 10 -11 mol L -1 under deliquesced aerosol conditions to 10 -13 -10 -12 mol L -1 under cloud conditions, are in a reasonable agreement with reported triplet concentrations in aerosols (2.3•10 −13 − 1.6•10 −10 mol L -1 estimated by Wang et al (2020)), in 60 fog samples (0.07−1.5•10 −13 (Kaur and Anastasio, 2018)) and in natural surface waters (10 −14 -10 −13 (Zepp et al, 1985;Canonica et al, 1995)). In the following paragraphs, the data compiled in Tables S3 and S4 are briefly discussed.…”

Global Importance of Hydroxymethanesulfonate in Ambient Particulate Matter: Implications for Air Quality

“…It is also the dominant aerosol component of climate forcing (Myhre et al, 2013). However, models can have difficulty reproducing particulate sulfur observations especially during winter, and as a result a variety of chemical mechanisms have been proposed as nonphotochemical sources of sulfate (Alexander et al, 2009;Cheng et al, 2016;Moch et al, 2018;Shah et al, 2018;Shao et al, 2019;Wang et al, 2014Wang et al, , 2020Zhang et al, 2012). Additionally, simultaneous measurements of sulfate and total elemental particulate sulfur have sometimes revealed a puzzling mismatch, given that sulfate has long been assumed to be the only particulate sulfur compound of significance (He et al, 2001;Shakya & Peltier, 2013;Tolocka & Turpin, 2012).…”

A Comprehensive Observational Based Multiphase Chemical Model Analysis of the Sulfur Dioxide Oxidations in both Summer and Winter

“…The missing contribution may mainly come from other pathways such as photosensitizing molucules (Wang et al, 2020) under stronger UV in summer or contributions from hydroxymethane sulfonate (Moch et al, 2018;Ma et al, 2020) which need further studies.…”

“…Other studies (Ye et al, 2018;Liu et al, 2020b) emphasized the importance of H2O2 oxidation to sulfate formation due to the underestimation of H2O2 concentrations during haze episodes in previous studies or the influence of high ionic strength (Is) of aerosol solutions on the H2O2 oxidation rate, which implies that oxidant concentrations for SO2 oxidation constrained to the observed values from field measurements are required. Previous study (Wang et al, 2020) showed that photosensitization is a new pathway for atmospheric sulfate formation and requires further verification. According to previous studies of the GEOS-Chem model and including the measurements of oxygen isotopes (Δ 17 O (SO4 2− )) (He et al, 2018;Shao et al, 2019;Li et al, 2020a;Yue et al, 2020), several studies showed that aqTMI was important during some haze periods.…”