AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
The Role of Aqueous Chemistry in Cloud Formation: Impact of Oligomerization
SHUNSUKE NAKAO, Yong Lim, Barbara Turpin, Alexandra Boris, Jeffrey Collett, Sonia Kreidenweis, Colorado State University
Abstract Number: 386 Working Group: Aerosols, Clouds, and Climate
Abstract Aqueous reactions in clouds or hydrated haze particles are potentially significant pathways for secondary organic aerosol (SOA) formation; SOA formed via aqueous reactions is termed aqSOA. One of the characteristics of aqSOA is that it is generally highly oxidized (high O/C), and hence expected to have high hygroscopicity. Therefore, aqSOA may play a key role in cloud droplet activation (and subsequent evaporation and activation cycles) at low supersaturation conditions. Recent studies have reported oligomer formation through aqueous reactions, possibly via radical-radical combination at the high organic concentrations typically encountered in wet aerosols. The oligomerization process may increase aqSOA mass by producing low vapor pressure products; however, it may also lower particle hygroscopicity by increasing molar volume (based on Raoult’s law).
In this study, we examined pyruvic acid (PA) photolysis as a simplified system of oligomerization with the following aims: 1) evaluating the impact of oligomerization in terms of aqSOA formation and CCN activity, 2) evaluating the relative importance of oligomerization to ammonium salt formation, and 3) evaluating the effectiveness of molar-volume based parameterization of the single hygroscopicity parameter, kappa, over the commonly used O/C parameterization. Oligomerization of the PA photolysis products resulted in an increase of molar volume of reaction products while keeping O/C nearly constant, making this a suitable system for exploring the impact of aqueous oligomerization on CCN activity. The aqueous reaction products were separated by ion chromatography before size-resolved CCN measurements, allowing detailed analysis beyond the conventional bulk O/C parameterization. Prediction of kappa based on reaction products will be discussed.