Testing the Photosensitized Production of Sulfate Radicals in Ammonium Sulfate Aerosol Liquid Water Mimics

ANGELINA PETERSEN, Tran Nguyen, University of California, Davis

     Abstract Number: 534
     Working Group: Aerosol Chemistry

Abstract
Organosulfates (OS) are ubiquitous in atmospheric aerosols and can modify aerosol-cloud interactions through reducing surface tension, yet many of their formation pathways are still poorly understood. Recently, it was reported that high ionic strength aqueous solutions of ammonium sulfate (AS) and other sulfate salts, representative of aerosol liquid water, can generate sulfur-containing radicals when irradiated with tropospheric sunlight, and thus initiate the formation of OS in the presence of organics. This work examines the hypothesis that chromophoric organic species, such as atmospheric brown carbon, can photosensitize the AS photochemistry under tropospheric conditions. The sulfate radicals may then add to a carbon-carbon double bond to form OS. We found that chromophores that can form triplet carbon excited states such as 3,4-dimethoxybenzaldehyde (3,4-DMB) decayed significantly and more rapidly when irradiated in the presence of AS than without. A sulfate radical trap with an aliphatic double bond was used to monitor the OS production yield. The variability in the OS yield between the irradiated high ionic strength AS + alkene solution, AS + alkene + chromophore solution, and their direct photolysis controls were investigated using high-performance liquid chromatography (HPLC) coupled to a high-resolution mass spectrometer (HRMS).