10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Source Apportionment, Wind Transport and Atmospheric Transformation of Carbonaceous Aerosol in the San Joaquin Valley, California
BENJAMIN DE FOY, Michael Olson, Alexandra Lai, Min-Suk Bae, Qingyang Liu, Matthew Skiles, James Schauer, St. Louis University
Abstract Number: 795 Working Group: Source Apportionment
Abstract PM2.5 samples were collected in Fresno and Bakersfield, California, from Jan 2015 to Feb 2016. The samples were collected over 24 hours every third day, matching the samples from the Environmental Protection Agency’s Chemical Speciation Network (EPA CSN). Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF) were applied to the chemical composition of the samples to obtain estimates of major sources contributions to ambient carbonaceous aerosols. There was a strong seasonality in the contributions of some sources as well as dependence on wind transport. Meteorological analysis of surface winds and radar wind profiler data was applied to distinguish the impact of source variations, chemistry and wind transport on the sample concentrations. Back-trajectories using WRF-FLEXPART were used to further characterize wind transport and residence times in the Central Valley. Clustering of the trajectories revealed dominant wind patterns and were combined in a multiple linear regression model to identify source regions. The meteorological analysis further revealed the importance of stable atmospheric conditions in the valley and the impact of the “Fresno Eddy” in contributing to air quality exceedances. The results from the fourteen-month study were compared with long term trends based on measurements of criteria pollutants from the Air Quality System (AQS). These were available at multiple sites in the valley at an hourly resolution, which provided a database with hundreds of thousands of data points. Analysis of these time series was used to estimate the trends in emissions on an annual, seasonal, weekly and diurnal timescale. The AQS data also provided constraints on the impact of transport and meteorology on high pollution events and air quality exceedances. By combining the analysis of speciated aerosol measurements with long time series of criteria pollutants, the analysis identified improvements in air quality over the last decade and avenues for future improvements.