Organosulfates in cloud water above the Ozarksʹ isoprene source region

Secondary organic aerosol formation via aqueous processing, particularly from the oxidation of biogenic volatile organic compounds, is hypothesized to contribute significantly to the global aerosol burden. In this study, electrospray ionization coupled with mass spectrometry (ESI-MS) was utilized to detect organosulfates and oligomers in cloud water collected in July above the Missouri Ozarks, an environment significantly influenced by isoprene oxidation. Community Multiscale Air Quality (CMAQ) modeling suggested that the aerosol at cloud height was characterized by high water, sulfate, and biogenic secondary organic aerosol content, conducive to aqueous-phase processing and organosulfate formation. CMAQ modeling also suggested the presence of gas-phase organic peroxides and nitrates, which can partition into the particle-phase and form organosulfates. Several potential organosulfates from isoprene, monoterpene, and sesquiterpene oxidation were detected in the cloud water. In particular, the ubiquitous organosulfate C5H12O7S (detected by ESI-MS at m/z −215), derived from isoprene epoxydiols, was detected. These results highlight the role of aqueous-phase reactions in biogenic SOA formation and cloud processes in isoprene oxidation-influenced regions.