AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Vapor Wall Loss of Semi-Volatile Organic Compound in Smog Chamber
PENGLIN YE, Xiang Ding, Ellis Shipley Robinson, Neil Donahue, Carnegie Mellon University
Abstract Number: 247 Working Group: Aerosol Chemistry
Abstract We have investigated the vapor wall loss of semi-volatile organic compounds (SVOCs) in the CMU smog chamber. Wall loss is a key factor influencing organic aerosols behavior in chamber experiments. Previous studies of wall loss focused on the loss of particles to the chamber wall. However, little knowledge is available about vapor wall loss that is due to the condensation of organic vapors on or into Teflon chamber walls. Matzunaga and Ziemann showed that organic vapors could sorb reversibly into Teflon chamber walls, but direct observations of semi-volatile vapor wall losses are lacking. We have studied the passive decays of alkanes (hexacosane, pentacosane, docosane, eicosane, d62-squalane) and an organic acid (oleic acid) in single-component and binary-component (organic) systems, using ammonium sulfate (AS) seeds to constrain particle wall loss (WLp). The organic to sulfate ratio (O:S) is a robust measure of mass loss; for pure organics coating AS, the coated aerosols sustain SVOCs at their saturation concentration, and so mass loss of organics from the suspended particles reflects vapor wall loss. For all organics studied here, O:S decreased steadily, clearly indicating significant vapor wall loss (WLv). This confirms that it is important to characterize WLv of SVOCs in chamber experiments. The WLv of the alkanes increased decreasing carbon number. Eicosane had the highest WLv and hexacosane showed quite small WLv. This indicated WLv was positively related to the volatility of SVOCs. The WLv of pure oleic acid and the mixture of oleic acid and d62-squalane were also studied. Pure oleic acid showed larger WLv than in the mixture. And the WLv of oleic acid in the mixture was positively correlated with the fraction of oleic acid in the mixture. Our results confirm that WLv needs to be considered in smog-chamber study, especially when evaluating the secondary organic aerosol (SOA) formation from SVOCs as well as OA evolution.