10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Volatility and Chemical Characterization of Secondary Organic Aerosols Formed from Aqueous-Phase Oxidation
SARAH SUDA PETTERS, Barbara Turpin, University of North Carolina at Chapel Hill
Abstract Number: 1334 Working Group: Aerosol Chemistry
Abstract Oxidized organic matter makes up a large fraction of the global aerosol burden and exerts an important influence on regional climate, human health and wellbeing, and the visibility of distant landmarks. Secondary organic aerosol (SOA) is formed when organic gases are oxidized and their reaction products condense. Condensed organic matter formed from the aqueous oxidation of water-soluble organic gases in cloud droplets and wet aerosols is increasingly recognized to be an important SOA contributor. However, quantifying the contribution of aqueous-phase mechanisms to SOA remains challenging. A major variable in determining aerosol yield is the volatility of the reaction products of aqueous-phase oxidation. A more detailed understanding of reaction products and their volatility is needed. Here we present the experimentally-determined volatility of SOA produced by aqueous oxidation of several precursors including pyruvic acid and methyl vinyl ketone. Oxidized organic matter was produced in a batch reactor containing an aqueous mixture of dissolved precursor and hydrogen peroxide. OH radicals were produced by photolysis of the hydrogen peroxide through ultraviolet irradiation. Samples were collected at intervals and chemical characterization was performed using ion chromatography (IC) and quadrupole time-of-flight mass spectrometry (QTOF-MS). Volatility was determined by pumping the sample through a vibrating orifice aerosol generator (VOAG), which produces a stream of monodisperse droplets of known size. Water and volatile compounds were evaporated at 20 degrees C and the particle residual volume was determined by an optical size spectrometer. The volume fraction remaining was determined by comparison of droplet residuals to the total organic carbon (TOC) in each sample, and volatility was estimated by comparison to calibration experiments using compounds of known volatility. Results show the dependence of volatility of aqueous oxidation products on concentration and on perturbations in solution pH made by the added presence of ammonium. Of particular interest are the volatilities of pyruvic acid aerosols in the context of the mechanisms of both pyruvic acid formation in the atmosphere and of aqueous aerosol formation from pyruvic acid. Recommendations for further investigation are discussed.