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ORGANIC AEROSOL FORMATION IN THE HUMID, PHOTOCHEMICALLY-ACTIVE SOUTHEASTERN US: SOAS EXPERIMENTS AND SIMULATIONS
Impact/Purpose:
Water is the most abundant fine particulate matter species in the eastern US, and yet its impact on ambient secondary organic aerosol formation is poorly understood. This proposal makes use of aqueous OH radical oxidation experiments conducted with ambient samples and evaluation of intermediate model products to improve mechanistic linkages between emissions and secondary organic species (gases and aerosol) in the humid, photochemically-active eastern United States (RFA Q#2). The proposed research is designed to be an integral part of the Southern Oxidant and Aerosol Study (SOAS), a collaborative field campaign taking place in a southeastern location influenced by biogenic emissions and with varying impacts from anthropogenic sources (RFA Q#1). We expect this work to ultimately lead to the development of more effective air quality management through models that better capture critical atmospheric processes. We hypothesize that chemistry that takes place in atmospheric waters has a substantial impact on the formation and properties of organic aerosol (note: we expect that gas-phase chemistry followed by aqueous chemistry will form SOA which is more hygroscopic and has higher O:C ratios). Gas phase photochemical reactions fragment and oxidize organic emissions, leading to the abundant formation of small, polar compounds (e.g., acetic acid, glyoxal, methylglyoxal, glycolaldehyde, acetone) that readily partition into cloud, fog and aerosol waters. Subsequent reactions in the aqueous phase can form low volatility products (e.g., organic acid salts, oligomers) that remain in the particle phase even after water evaporation. Thus, in an environment where photochemistry and abundant liquid water coexist, gas followed by aqueous chemistry could be the predominant source of secondary organic aerosol (SOA). The SOAS campaign is an ideal opportunity to test this.
Description:
A better understanding of SOA formation, properties and behavior in the humid eastern U.S. including dependence on anthropogenic emissions (RFA Q #1, 2). More accurate air quality prediction enabling more accurate air quality management (EPA Goal #1). Scientific insights communicated via peer-reviewed publications and other means.