AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Drying-Induced Evaporation of Secondary Organic Aerosols during Summer
Marwa El-Sayed, Dziedzorm Amenumey, CHRISTOPHER HENNIGAN, University of Maryland, Baltimore County
Abstract Number: 60 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Aerosol liquid water can play a pivotal role in the formation of secondary organic aerosol (SOA) from biogenic VOCs. Anthropogenic emissions of sulfur and nitrogen oxides contribute to aerosol liquid water levels, and thus, to the aqueous formation of SOA from biogenic VOCs. However, many aspects of these interactions are unknown at present, including the relative contributions of reversible and irreversible uptake processes to SOA formed in aerosol water. Ambient measurements were conducted in Baltimore, MD to characterize the effects of particle drying on SOA concentrations during the summertime. On-line measurements of particulate water-soluble organic carbon (WSOC$_p), a surrogate for SOA, were alternated between an unperturbed ambient channel and a “dried” channel maintained at ~35% relative humidity. WSOC$_p concentrations measured through the dried channel were systematically lower than the ambient WSOC$_p concentrations: the average mass ratio between the two measurements was 0.85, showing that significant evaporation of the organic aerosol occurred due to drying. The average amount of evaporated water-soluble organic matter (WSOM = WSOC × 1.95) was 0.6 micro-grams per cubic meter; however, the maximum evaporated WSOM concentration exceeded 5 micro-grams per cubic meter, demonstrating the importance of this phenomenon. The systematic difference between ambient and dry channels indicates a significant and persistent source of aqueous SOA formed through reversible uptake processes. These results have important implications for our understanding of SOA formation from biogenic VOCs, including new insight into the measurement methods commonly used to characterize this process.