AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Effect of Ambient Primary Organic Aerosols on Secondary Organic Aerosol Formation
JIANHUAI YE, Bruce Urch, Greg J. Evans, Arthur Chan, University of Toronto
Abstract Number: 58 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) is known to pose serious health effects and plays a significant role in global climate change. Current atmospheric models assume that all organic species, including both primary organic aerosol (POA) and SOA form a well-mixed liquid phase and oxidation products partition into POA similarly as into SOA. Under this assumption, gas/particle partitioning equilibria for different SOA systems are parameterized in laboratory experiments (Odum model, volatility basis set etc.) with SOA-only organic phases.
Recently, Song et al. (Geophys. Res. Lett., 2007) demonstrated that SOA yield of alpha-pinene ozonolysis was not enhanced by introducing dioctyl phthalate and lubricating oil (POA surrogates) as expected, which indicated the overestimation of the results from the “Odum model”. Similarly, Asa-Awuku et al. (Geophys. Res. Lett., 2009), showed that different POA compositions may result in distinct phase partitioning behaviours. In both cases, the POA were laboratory-generated.
In this work, we examine the validity of “single phase” assumption by studying the interactions between ambient POA and SOA from the ozonolysis of alpha-pinene. The study is conducted adjacent to a major roadway in Toronto, Canada. Ambient POA is introduced into a custom-made quartz reactor (10.2 cm I.D. × 120 cm L.) together with alpha-pinene and oxidized with ozone. Aerodyne Aerosol Chemical Speciation Monitor (ACSM) will be used to determine the chemical compositions of POA. Aerosol size distributions and number concentrations are measured using a Scanning Mobility Particle Sizer (SMPS). Alpha-pinene concentrations are monitored using GC-FID.
In this study, we compare the experimental SOA yields of alpha-pinene ozonolysis in the presence of ambient POA to those predicted from the “Odum model”. In addition, POA/SOA phase partitioning behaviours are investigated with varying POA compositions during the day. Finally, the role of humidity in POA/SOA phase partitioning is also examined.