AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Photolytic Processing of Organic Atmospheric Particulate Matter
SCOTT A. EPSTEIN, Mallory Hinks, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 47 Working Group: Aerosol Chemistry
Abstract The organic multifunctional compounds including peroxides, carbonyls, and nitrates typically found in organic particulate matter (PM) are photolabile and decompose when exposed to solar radiation on atmospherically relevant time scales. Many of these organic molecules and their photolysis products are semi-volatile, and depending on conditions, can have significant concentrations in both the gas and condensed phase. Most past experiments designed to characterize the photochemistry of organic PM mixtures involve photolysis of both gas and condensed phase species inside a reaction chamber. While these experiments reveal the overall behavior of the aerosol mixture, the semi-volatile nature of the constituents makes it difficult to distinguish between direct photolysis and photooxidation processes occurring in the gas phase and the condensed phase. We have designed and built a flow cell system to study the photolysis of organic particulate matter in absence of its corresponding vapors. After sending an organic aerosol mixture through several large denuders lined with activated charcoal to remove gas phase species, residual particles enter a photolysis flow cell containing UV lamps designed to simulate solar radiation. The photolysis chamber contains a large surface area of continuously cooled activated charcoal to remove vapors evolved from PM photolysis. The intensity of radiation exposure is quantified using chemical actinometry methods. Particle composition with and without UV radiation is monitored in real-time with an Aerodyne HR-ToF-AMS. In addition, off-line analysis of particle composition using methods of ultra-high-resolution mass spectrometry provides additional molecular level information about the aerosol constituents. These experiments reveal the effects of solar radiation on several different types of organic particulate matter derived from anthropogenic and biogenic precursors.