Sulfate Formation by Photosensitization in Mixed Incense Burning-Sodium Chloride Particles: Effects of RH, Light Intensity, and Aerosol Aging

摘要

Elevated particulate sulfate concentrations have beenfrequentlyobserved in coastal areas when air masses are influenced by continentalemissions, especially combustion sources like biomass burning. Westudied the SO2 uptake by laboratory-generated dropletscontaining incense smoke extracts and sodium chloride (IS-NaCl)under irradiation and found enhanced sulfate production over pureNaCl droplets, attributable to photosensitization induced by constituentsin IS. Low relative humidity and high light intensity facilitatedsulfate formation and increased the SO2 uptake coefficientby IS-NaCl particles. Aging of the IS particles further enhancedsulfate production, attributable to the enhanced secondary oxidantproduction promoted by increased proportions of nitrogen-containingCHN and oxygen- and nitrogen-containing CHON species under light andair. Experiments using model compounds of syringaldehyde, pyrazine,and 4-nitroguaiacol verified the enhancements of CHN and CHON speciesin sulfate formation. This work provides experimental evidence ofenhanced sulfate production in laboratory-generated IS-NaCldroplets via enhanced secondary oxidant production triggered by photosensitizationin multiphase oxidation processes under light and air. Our resultscan shed light on the possible interactions between sea salt and biomassburning aerosols in enhancing sulfate production. @@@ Enhanced sulfate formation was foundusing mixed incenseburning-NaCl droplets over pure NaCl droplets due to photosensitization.The enhancement increased with aged incense burning particles dueto the presence of CHN and CHON species.

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