The secondary formation of organosulfates under interactions between biogenic emissions and anthropogenic pollutants in summer in Beijing

Organosulfates (OSs), with ambiguous formation mechanisms, are a potential source of "missing secondary organic aerosol (SOA)" in current atmospheric models. In this study, we analyzed the characterization and formation of OSs and nitrooxy OSs (NOSs) under the influence of biogenic emissions and anthropogenic pollutants (e.g. NO x , SO 4 2− ) in summer of Beijing. The ultrahigh-resolution mass spectrometer equipped with electrospray ionization source was applied to examine the overall molecular composition of S-containing organics. The number and intensities of S-containing organics, majority of which could be assigned as OSs and NOSs, increased significantly during pollution episodes, which indicated their importance for SOA accumulation. To further investigate the distribution and formation of OSs and NOSs, the high performance liquid chromatography coupled to mass spectrometer was then employed to quantify ten representative OSs and three NOS species. The total concentrations of quantified OSs and NOSs were 41.42 and 13.75 ng/m 3 , respectively. Glycolic acid sulfate was the most abundant species among all the quantified species, followed by monoterpene NOSs (C 10 H 16 NO 7 S − ). The total concentration of three isoprene OSs was 14.77 ng/m 3 and the isoprene OSs formed via HO 2 channel was higher than those formed via NO/NO 2 channel. The OS concentration coincided with the increase of acidic sulfate aerosols, aerosol acidity and liquid water content, indicating the acid-catalyzed aqueous-phase formation of OSs in the presence of acidic sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols (SIAs) (SO 4 2− /SIAs > 0.5), OS formation would be obviously promoted as the increasing of acidic sulfate aerosols, aerosol LWC and acidity (pH  3 -initiated oxidation of monoterpene under high-NO x conditions. However, isoprene NOSs are supposed to form via acid-catalyzed chemistry or reactive uptake of oxidation products of isoprene. This study provides direct observational evidence and highlights the secondary formation of OSs and NOSs, via the interaction between biogenic precursors and anthropogenic pollutants (NO x , SO 2 and SO 4 2− ). The results imply that future reduction in anthropogenic emissions can help to reduce the biogenic SOA burden in Beijing or other areas impacted by both biogenic emissions and anthropogenic pollutants.