AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Source Apportionment of Carbonaceous Aerosol in the San Joaquin Valley, California – Sensitivity to Seasonal Variation
MICHAEL OLSON, Alexandra Lai, Min-Suk Bae, Qingyang Liu, Matthew Skiles, Benjamin de Foy, James Schauer, University of Wisconsin-Madison
Abstract Number: 730 Working Group: Source Apportionment
Abstract One-in-three day PM2.5 samples were collected at Bakersfield and Fresno California over a fourteen month time period in 2015 and 2016. Samples were collected in parallel with the Environmental Protection Agency Chemicals Speciation Network (EPA CSN) samples and were analyzed for elemental and organic carbon (EC/OC), water soluble organic carbon (WSOC) and organic molecular marker compounds. The EPA chemical mass balance (CMB) and positive matrix factorization (PMF) models were applied to identify major source contribution to ambient OC. The primary sources identified by CMB were biomass burning, mobile source, meat cooking, vegetative detritus and “Other OC” sources. The PMF model, used as an independent validation of the CMB results, identified biomass burning, mobile sources, food cooking, two SOA sources, and forest fire emissions. The models showed good agreement, identifying a strong wintertime contribution of biomass burning and a steady annual mobile source contribution. CMB profiles were applied to segregate the gasoline, diesel, and smoking vehicle contribution, however the mobile source split could not be identified due to observed collinearity. As a result, the CMB mobile was identified as the sum of CMB gasoline, diesel, and smoking vehicle. These results showed similar trends with the identified PMF mobile source. However, PMF OC apportionment was consistently larger than the CMB mobile, likely due to fast forming SOA Compounds. This is highlighted by the inclusion of secondary acids, typical of atmospheric oxidation, in the resulting source profile. Trend analysis of the organic compounds and meteorological simulations, performed using the Weather Research and Forecast (WRF) model, further allowed verification of the source apportionment results. Unique seasonal trends were identified for meat/food cooking sources and source specific organic tracers, which indicated sensitivity to both atmospheric processing and meteorological mixing and dilution. Biomass burning, food cooking, and CMB “other” showed strong seasonal trends. However, detailed understanding of these contributors requires trend analysis of chemical species and detailed meteorological analysis to develop an accurate understanding of source contribution to ambient PM mass over the annual cycle.