AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Molecular Composition and Photochemical Aging of Alpha-Pinene SOA and Alpha-Humulene SOA Generated Under Nocturnal and Diurnal Conditions
DIAN ROMONOSKY, Sergey Nizkorodov, Julia Laskin, Alexander Laskin, University of California, Irvine
Abstract Number: 106 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) formation readily occurs in reactions of biogenic volatile organic compounds (BVOC) with ozone (nighttime and daytime), OH/NO$_x (daytime), and NO$_3 radicals (nighttime). Each of the BVOC oxidation pathways may be expected to produce a uniquely different set of SOA compounds, with different physical properties. The main goal of this study was to explore the effect of each of these three oxidation conditions on the molecular composition and photochemistry of SOA prepared from common BVOC. A typical monoterpene (alpha-pinene) and sesquiterpene (alpha-humulene) were chosen to model SOA formation in a smog chamber via: (1) BVOC + O$_3, (2) BVOC + NO$_3, and (3) BVOC + OH + NO$_x + hv. In selected experiments, ammonia was added to the chamber after SOA formation to investigate its effect on SOA composition. The resulting SOA was collected on an inert substrate, extracted in water, and photolyzed in an aqueous solution in order to model the photochemical cloud-processing of SOA. The extent of change in the molecular level composition of SOA over 4 hours of photolysis was assessed with high-resolution mass spectrometry (HR-MS). The data were collected in spring of 2014, and will be fully analyzed in time for the AAAR meeting. However, the preliminary analysis revealed significant differences in the molecular composition between monoterpene and sesquiterpene SOA formed by the different oxidation pathways. The composition further evolved during photolysis. This study highlights the importance of aqueous photochemistry in the aging of biogenic SOA.