Chemical transformation of α-pinene-derived organosulfate via heterogeneous OH oxidation: implications for sources and environmental fates of atmospheric organosulfates

Organosulfur compounds are found to be ubiquitous in atmospheric aerosols - a majority of which are expected to be organosulfates (OSs). Given the atmospheric abundance of OSs, and their potential to form a variety of reaction products upon aging, it is imperative to study the transformation kinetics and chemistry of OS s to better elucidate their atmospheric fates and impacts. In this work, we investigated the chemical transformation of an alpha-pinene-derived organosulfate (C10H17O5SNa, alpha pOS-249) through heterogeneous OH oxidation at a relative humidity of 50 % in an oxidation flow reactor (OFR). The aerosol-phase reaction products were characterized using high-performance liquid chromatography-electrospray ionization-high-resolution mass spectrometry and ion chromatography. By monitoring the decay rates of alpha pOS-249, the effective heterogeneous OH reaction rate was measured to be (6.72 +/- 0.55) x 10(-13) cm(3) molecule(-1) s(-1). This infers an atmospheric lifetime of about 2 weeks at an average OH concentration of 1.5 x 10(6) molecules cm(-3). Product analysis shows that OH oxidation of alpha pOS-249 can yield more oxygenated OSs with a nominal mass-to-charge ratio (m/z) at 247 (C10H15O5S-), 263 (C10H5O6S-), 265 (C10H7O6S-), 277 (C10H3O7S-), 279 (C10H5O7S-), and 281 (C10H7O7S-). The formation of fragmentation products, including both small OSs (C < 10) and inorganic sulfates, is found to be insignificant. These observations suggest that functionalization reactions are likely the dominant processes and that multigenerational oxidation possibly leads to formation of products with one or two hydroxyl and carbonyl functional groups adding to alpha pOS-249. Furthermore, all product ions except m/z = 277 have been detected in laboratory-generated alpha-pinene-derived secondary organic aerosols as well as in atmospheric aerosols. Our results reveal that OSs freshly formed from the photochemical oxidation of alpha-pinene could react further to form OSs commonly detected in atmospheric aerosols through heterogeneous OH oxidation. Overall, this study provides more insights into the sources, transformation, and fate of atmospheric OSs.

Automated summary

This study investigated the chemical transformation of an alpha-pinene-derived organosulfate through heterogeneous OH oxidation and found that the oxidation can yield more oxygenated organosulfates with minimal formation of fragmentation products. The results suggest that functionalization reactions are likely the dominant processes during the oxidation, leading to the formation of products with hydroxyl and carbonyl functional groups. Overall, these observations provide insights into the sources, transformation, and fate of atmospheric organosulfates.