Application of a counting technique to determine certain and uncertain geographic regions of emission sources

Potential source contribution functions (PSCF) are frequently used to determine possible emission sources of airborne pollutants. A counting technique was developed to correct for regions erroneously identified by conventional PSCF. While conventional PSCF uses empirically determined weighting factors to correct for these erroneous regions, the proposed technique counts trajectories passing through a location of interest and in adjacent regions to objectively determine its identification as a source region. Conventional PSCF plots and modified version using this new counting technique were created for total PM2.5 and nitrate PM2.5 mass concentration data collected between July 2001 and September 2002. The modified PSCF eliminated erroneous potential emission sources regions and also identified potential emission sources during episodic events. These episodic source regions were not observed with conventional PSCF plots. The PSCF plots of total PM2.5 mass concentration displayed geographic regions where power plants in Southern Ontario, Michigan and Ohio were located. Similarly, the PSCF plots of nitrate PM2.5 mass concentrations displayed areas in Canada and the United States related to agricultural regions. Two episodic emission sources corresponding with forest fires in Quebec and the Prairie Provinces were also identified by the modified PSCF. Interestingly, the Prairie forest fires were identified as a nitrate source, unlike the Quebec forest fires.