AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Average Chemical Properties and Potential Formation Pathways of Highly Oxidized Organic Aerosol
KELLY DAUMIT, Sean Kessler, Jesse Kroll, MIT
Abstract Number: 282 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Measurements of ambient organic aerosol indicate that a substantial fraction is highly oxidized and low in volatility, but this fraction is generally not reproduced well in either laboratory studies or models. From field measurements, we know that low-volatility oxidized organic aerosol (LV-OOA) is highly oxidized (with an average carbon oxidation state of approximately 0-1), exceedingly low in volatility (c* ~0.1 to <10$^(-7) ug m$^(-3)), and generated relatively quickly (over time scales of ~1-3 days). Thus the atmospheric formation of LV-OOA must involve reactions that rapidly increase the oxidation state of organic carbon (i.e., increasing O:C and decreasing H:C) while also rapidly decreasing the vapor pressure of the organics. In this work, we describe a new approach for constraining the viable precursors and formation pathways of LV-OOA, by starting with the oxidized product and considering the possible reverse reactions, using a simple set of chemical rules. The elemental composition and volatility of the aerosol enables the determination of its position in three-dimensional chemical space (defined by H:C, O:C, and carbon number) and its average chemical formula. Consideration of possible back-reactions then defines the movement taken through this chemical space, constraining potential reaction pathways and precursors. Results suggest that potential LV-OOA formation pathways include functionalization reactions that add multiple functional groups per oxidation step, oligomerization of highly oxidized precursors, and, in some cases, fragmentation reactions that involve the loss of small, reduced fragments.