Exploring the fate of organosulfates in the atmospheric aqueous phase

Abstract:

Organosulfates (R–OSO₃^-, OS), are ubiquitous in the atmosphere: large-scale studies have estimated that OS contribute 5–10% of particulate matter (PM) over the United States, and up to 30% over coastal and Arctic sites. As they are hygroscopic, OS can influence cloud-forming properties of PM; in addition, they are tracers of sulfate derived biogenic secondary aerosol. Although the formation pathways of OS are now fairly well-understood, comparatively little is known regarding their atmospheric fate. Because OS are highly acidic and water-soluble, they are expected to reside primarily in the tropospheric condensed phase rather than the gas phase. In this study, we use a competition kinetics approach to investigate the aqueous phase hydroxyl radical (OH) oxidation kinetics of a suite of atmospherically relevant OS. In addition, we examine the effects of OS structural properties (carbon chain length, aromaticity, and functionalization) and reaction conditions (pH and ionic strength) on the observed rate constants. To better understand the transformation mechanisms of this class of compounds, we also identify the oxidation products of these reactions. This study represents a significant advance in our understanding of the atmospheric fate of OS: in particular, it presents for the first time, the atmospheric reactivities and compositional evolution of OS in the aqueous phase and provides valuable information for inclusion in atmospheric models.