where mij is the number of endpoints for ijth cell having times of arrival at the sampling site corresponding to pollutant concentrations higher than a given reference value. The mean concentration of particulate pollutants is always selected as the reference value [Cheng et al., 2006; Wang et al., 2004]. The value nij means the number of all endpoints that fall in the same cell. Cells with high Potential source contribution function (PSCF) values are associated with the arrival of air parcels at the receptor site with pollutant concentrations higher than the given reference value. These cells indicate that the regions are high potential contributions to the pollution at the receptor site.