AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Seasonal Characterization of SOA Formed through the Uptake of Water-Soluble Gases to Aerosol Liquid Water (aqSOA)
MARWA EL-SAYED, Christopher Hennigan, University of Maryland, Baltimore County
Abstract Number: 12 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The formation of secondary organic aerosols through aqueous processes (aqSOA) has been identified as an important route in forming organic aerosols; however, many aspects of aqSOA formation are still uncertain. The aim of this ambient study was to characterize the reversible and irreversible formation of aqSOA across the four seasons to provide insight into the main factors which govern the uptake of organic gases into aerosol liquid water. The reversible and irreversible uptake of water-soluble organic gases in liquid water was measured in Baltimore, MD using a recently developed on-line method. Not only did the amount of aqSOA vary across the seasons, but also there were strong seasonal differences in the reversible and irreversible nature of the uptake of gases into liquid water. Irreversible aqSOA formation was observed in all four seasons, and was a strong function of relative humidity (RH). On the other hand, reversible aqSOA formation was only observed during the late spring and throughout the summer, where it accounted for 10-15% of the total SOA formed in these two seasons. During the periods where reversible aqSOA was observed, its concentrations were of the same order as irreversible aqSOA, indicating the importance of both processes in the eastern United States. Based on the seasonal differences observed in aqSOA formation, some of the factors underlying the differences in the concentrations of reversible and irreversible aqSOA are investigated, which include: temperature, RH, precursor VOC emissions, mixing and transport.