Evaluation of Source Apportionment and Source Sensitivity of Fine Particulate Matter

Fine particulate matter (PM2.5) is a widely studied pollutant that has been linked to a variety of health problems including decreased lung function and chronic bronchitis. In December 2006 the EPA lowered the 24-hour PM2.5 standard from 65 to 35 µg/m3. As of March 2009, 208 counties are in non-attainment of this new standard. Source apportionment is a method of quantifying the relative impacts of different emission sources on PM2.5 formation and provides valuable information that can be used in the formulation of emission reduction strategies. While source apportionment has traditionally been achieved by solving the equation for conservation of mass, more recent studies have utilized 3-dimensional air quality models. In this study, the Particulate Source Apportionment Technology (PSAT) available in the Comprehensive Air Quality Model with Extensions (CAMx) is used to conduct source apportionment for PM2.5 at a 12-km horizontal grid resolution over the eastern U.S. for the months of January and July 2002. PSAT is based on the reactive tracer method, in which additional tracer species within the model track particle formation from different emission sources. Two CAMx/PSAT simulations are being conducted to determine the contributions of the ten source categories for both months. These results will be compared with source sensitivity results using the brute force method from the Community Multiscale Air Quality (CMAQ) modeling system. The results from PSAT in CAMx and the brute force method with CMAQ will be evaluated along with discussions of likely causes for the major differences and similarities between the resolved source contributions from each method. Additionally, the relative importance of each source category and their potential implications on source-oriented emission control strategies will be examined.