Abstract View
Measuring Brown Carbon Aerosol Deliquescence: Effect of Reaction Time and Composition
RACHEL M. HESGARD, Ariana Cruz Cruz, Paula K. Hudson, California State University, Fullerton
Abstract Number: 526
Working Group: Aerosols, Clouds and Climate
Abstract
Atmospheric brown carbon (BrC) is a class of light absorbing secondary organic aerosol (SOA), which range in color from light yellow to dark brown. Measuring the hygroscopic properties of atmospheric BrC, and the role of cloud cycling on aerosol hygroscopicity, are essential to understanding the overall effect that BrC aerosol have on climate. To better understand and predict cloud formation properties of BrC, aerosol are generated from aqueous phase laboratory reactions of glyoxal (GX) and glycine (Gly). The composition of the BrC varied in initial reactant composition, using 2:1, 1:1 and 1:2 mole ratios of GX:Gly, and reaction time, after 3, 51, and 165 days of reaction. The water uptake and deliquescence of BrC aerosol was measured using a quartz crystal microbalance (QCM). BrC particles deposited on the quartz crystal are first dried then exposed to increasing relative humidity resulting initially in decreases in crystal oscillation frequency (water adsorption) then increases in oscillation frequency (deliquescence). The effect of cloud cycling on BrC deliquescence was also examined by repeatedly measuring the deliquescence relative humidity (DRH) of an individual BrC sample after drying each time. Although reaction time has a large effect on the light absorption of the BrC aerosol, there is no effect on the measured DRH supporting previous reports of a single BrC product formed from glycine / glyoxal reactions. As expected, DRH increases from 74% to 89% with increasing glycine concentration given the much higher DRH of glycine relative to glyoxal. Similarly, DRH increases from 74% to 85% over five “wet-dry” cycles, suggesting BrC composition becomes more glycine-like due to glyoxal evaporation from aqueous droplets. Results suggest that while reaction time or cloud cycling enhances the warming direct effect of BrC, these processes have no effect, or a negative effect, on cloud formation.