AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
A Smog Chamber-Flow Tube Study of the Direct Photolysis of Model Biogenic and Anthropogenic SOA
SANDRA BLAIR, Scott A. Epstein, Amanda MacMillan, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 22 Working Group: Aerosol Chemistry
Abstract The physical properties and toxicity of “fresh” versus “aged” secondary organic aerosol (SOA) strongly depend on the type of aging. This paper focuses on SOA aging arising from the condensed-phase photolysis of particulate organic compounds. Previous studies of SOA aging have mainly relied on the photooxidation of SOA in smog chambers or in flow reactors. However, in these types of studies, it is challenging to isolate the effect of condensed-phase photolysis from gas-phase photochemical reactions followed by gas-to-particle partitioning. We designed and carried out experiments that produced SOA in a smog chamber, stripped the excess oxidants and gaseous organics with a denuder train, photolyzed the resulting particles in a quartz flow tube, and analyzed the SOA composition and mass concentration before and after direct photolysis of particulate organic compounds using various analytical techniques. The unique advantages of this method include the ability to exclude possible interfering factors caused by (1) oxidant recycling, (2) gas-phase photolysis of high-volatility organic compounds, and (3) dark aging. We will discuss the results for two model systems: alpha-pinene ozonolysis SOA and diesel photooxidation SOA prepared in the presence and absence of SO$_2. Specifically, we will discuss the effect of UV photolysis on (1) particle mass concentration, (2) overall peroxide content, (3) chemical composition as measured by an aerosol mass spectrometer (AMS), (4) mass absorption coefficient, and (5) oxidative stress by particle suspensions as measured by a rapid kinetic bioassay demonstrating the inhibition of glutathione peroxidase 1 (GPx-1) by organic electrophilic pollutants. The health and climate implications of these measurements will be discussed.