Source apportionment study of nitrogen species measured in Southern California in 1987

A novel receptor-oriented methodology has been developed to apportion source contributions of the nitrogen species measured in the south coast air quality basin (SoCAB) in the 1987 southern California air quality study (SCAQS). This method begins by calculating a conditional probability field [potential source contribution function (PSCF)] relating the probability of a 5 km by 5 km area to observed high concentrations at a receptor site. Comparison of the locations of known sources with areas of high PSCF values indicates the power of the PSCF results. The source contribution of a grid cell (i.e., a source area) was then computed by multiplying the available emissions inventory emissions rate by the PSCF value and including the contributions from the species into which the emitted compounds could be transformed. The probability weighted emission rate can then be interpreted in terms of source contribution "as observed" at the receptor site. The estimated source contribution includes the atmospheric transport, removal, and transformation processes. The PSCF-constructed source apportionment map could be effective in the design of emission control strategies than emission inventory values, because the PSCF results indicate the actual impact of each grid source on the total amount of material received at the receptor site.