AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Direct Atmospheric Evidence for the Irreversible Formation of Aqueous Secondary Organic Aerosol (aqSOA)
Marwa El-Sayed, Yingqing Wang, CHRISTOPHER HENNIGAN, University of Maryland, Baltimore County
Abstract Number: 188 Working Group: The Role of Water in Aerosol Chemistry
Abstract The reversible nature of aqueous secondary organic aerosol (aqSOA) formation was characterized for the first time through direct atmospheric measurements. Water-soluble organic carbon in the gas- and particle phases (WSOCg and WSOCp) was measured simultaneously to quantify aqSOA formation in Baltimore, MD. During both daytime and nighttime periods, aqSOA formation was evident as WSOCg increasingly partitioned to the particle phase with increasing relative humidity (RH). To characterize the reversible/irreversible nature of this aqSOA, the WSOCp measurement was alternated through an unperturbed ambient channel and through a ‘dried’ channel maintained at ~40% RH to mimic the natural drying particles may undergo over the course of a day. Across the entire ambient RH range encountered, there was no statistically-significant difference in the WSOCp concentrations measured through the dry and ambient channels. This included the periods of active aqSOA formation, indicating that the aqSOA remained in the condensed phase upon the evaporation of aerosol water. This strongly suggests that the observed aqSOA was formed irreversibly and has important implications for our understanding of organic reactions in fine particle water.