Role of Criegee Intermediates in Secondary Sulfate Aerosol Formation in Nocturnal Power Plant Plumes in the Southeast US

Criegee intermediates (CI) from ozonolysis of biogenic volatile organic compounds (BVOC) have been suggested to be important atmospheric oxidants. However, due to their low atmospheric concentrations, possible high reactivity with water vapor, and unconstrained thermal unimolecular decay rates, their impact on atmospheric oxidation of trace species such as SO2 and NO2 remains uncertain. In this study, we investigate the formation of secondary sulfate aerosols (SSA) in nocturnal power plant plumes in the Southeastern US. These plumes have large mixing ratios of SO2 and NOx that make reaction with CI competitive with other pathways, such as thermal unimolecular decay and water vapor reaction. The background into which these plumes are emitted has high levels of BVOC and O3, whose reaction produces a large source of CI. Observed nighttime power plant plume intercepts had measurable sulfate aerosol, ranging from 0.7–1.2% of the total plume sulfur (SO2 + sulfate) on a molar basis. In the absence of photochemic...