Comparative Study of Particulate Organosulfates in Contrasting Atmospheric Environments: Field Evidence for the Significant Influence of Anthropogenic Sulfate and NO_x

Abstract

Organosulfates (OSs) are an important group of secondary organic aerosols, but the key influential factors of their formation in polluted atmospheres are not well understood. In this study, we monitored particulate OSs (carboxy OSs, hydroxyacetone sulfate, and isoprene- and monoterpene-derived OSs) at an urban site and a regional site in Beijing and examined their compositions and formation pathways under contrasting atmospheric conditions. The quantified OSs were most abundant in the summer at the regional site due to higher biogenic emissions and favorable formation conditions (higher aerosol acidity and humidity), followed by urban summer and winter conditions. Larger fractions of inorganic sulfate were converted to organosulfur when sulfate was less abundant. This implies that OSs would play more important roles in aerosol properties as the decline of sulfate. Monoterpene-derived nitrooxy-OSs were enhanced via NO3 oxidation in the summer under high-NO x conditions at night, while the day–night variations in the winter were not as obvious. Among isoprene-OSs, IEPOX (isoprene epoxydiols)-OS formation was clearly suppressed under high-NO x conditions, while other isoprene-OSs that are favored under high-NO x conditions showed increasing formation with NO x . The results highlight that isoprene-OS formation pathways in polluted atmospheres could be different from the IEPOX-dominated regions reported for the low-NO x environments in the literature.

Interactions of organosulfates with water vapor under sub- and supersaturated conditions

“…Organosulfates (OSs), which could contribute to the total mass of ambient organic aerosols by as much as 30 %, may largely explain the discrepancy between observed and modeled global SOA budgets (Surratt et al, 2008;Tolocka and Turpin, 2012;Liao et al, 2015). A number of field measurements have observed significant amounts of OS in ambient aerosols in different regions over the globe (Froyd et al, 2010;Kristensen and Glasius, 2011;He et al, 2014;Hettiyadura et al, 2015;Riva et al, 2019;Zhang et al, 2019;Bruggemann et al, 2020;Wang et al, 2020). For example, the mass concentration of sodium methyl sulfate, the smallest organosulfate, was found to be 0.2-9.3 ng m −3 in Centreville, Alabama (Hettiyadura et al, 2017).…”

Molecular Characteristics of Organosulfur Compounds in Guangzhou, South China: Heterogeneous Secondary Reactions Drivers the Molecular Distribution

“…Moreover, directly assessing relationships between individual compounds and LWC, NO3 − , NH4 + suggested that the increase of their concentrations would promote the formation of CHONS species, as 72%, 65% and 75% of the OrgSs that have positive correlations (p adjust with "fdr") with the LWC, NO3 − , NH4 + , are CHONS species (Table S13), respectively, further supports the OrgSs formation via aqueous-phase chemistry in Guangzhou influenced by LWC, such as NO3-initiated oxidation, acidcatalyzed epoxide pathways (Wang et al, 2020;Xu et al, 2021b). Recently, Bryant et al (2021) reported that oxidants and temperature are important factors that affect OSs formation in Guangzhou, and high-NOx pathways became more important in the winter when usually suffering high anthropogenic emissions, while low-NO formation pathways were dominant in the summer.…”

Secondary Formation of Aerosols Under Typical High‐Humidity Conditions in Wintertime Sichuan Basin, China: A Contrast to the North China Plain

“…Secondarily, the aerosol acidity in Sichuan was higher than that in Beijing, with average predicted pH of 3.8 ± 0.6 and 5.3 ± 1.1, respectively, which favored the acid‐catalyzed OS formation in Sichuan. Previous chamber and field studies have suggested the importance of acid‐catalyzed reactions for OS formation (e.g., OSs from alkanes, isoprene, monoterpene and sesquiterpene) (Bruggemann et al., 2020; Chan et al., 2011; Iinuma et al., 2009; Lal et al., 2012; Riva et al., 2016; Surratt et al., 2010; Surratt et al., 2007; Y. Wang et al., 2018, Y. Wang, Hu, et al., 2020). Aerosol pH is highly related to the ratios of sulfate and nitrate when all else is equal, with lower pH (higher acidity) under sulfate‐dominated conditions (Guo et al., 2016).…”