Potential source contribution function analysis and source apportionment of sulfur species measured at Rubidoux, CA during the Southern California Air Quality Study, 1987

During the Southern California Air Quality Study (SCAQS) in summer and fall of 1987, specially designed SCAQS samplers were used to collect particles and gaseous species. Ion chromatography (IC) and colorimetry were employed to analyze the gaseous and particulate ionic species while the trace elements in the particles were analyzed using x-ray fluorescence (XRF). Potential source contribution function (PSCF) analysis was applied to the chemistry data of the acidic species collected by the SCAQS samplers at the Burbank, Claremont and Rubidoux sites and the meteorology data in the form of air parcel backward trajectories. The results are presented as gridded conditional probability maps showing source areas that have a potential to contribute to the high concentrations of acidic species observed at the receptor sites. In order to quantitatively determine the mass contributions of acidic species from these identified source areas to the receptor sites, a source apportionment method was developed that utilizes the PSCF analysis results and the ground and elevated level emission inventories. One result is a gridded joint probability map showing the quantities of emitted acidic species from source areas that were transported to the three receptor sites with and/or without undergoing chemical transformations during the transport. Another result is a gridded map for each single receptor site showing the possible maximum amounts of emitted acidic species from source areas that were transported to that receptor site with and/or without undergoing chemical transformations. The potential source areas identified by the PSCF analysis and the amount of transported emissions identified by the source apportionment method are generally well correlated with the emission inventories. The receptor modeling results of SO₂ and SO^2-₄ are presented to illustrate the methodology.