Validation of the Chemical Mass Balance Receptor Model Applied to Hydrocarbon Source Apportionment in the Southern California Air Quality Study

Abstract

The non-methane hydrocarbon (NMHC) data base acquired during the Southern California Air Quality Study (SCAQS) was used to assess the performance of the chemical mass balance (CMB) receptor model following the CMB applications and validation protocol. As a prelude to the actual CMB effective variance runs, initial source contribution estimates were made to determine the optimal combination of source profiles and fitting species. Several different source composition profiles were selected for major source types to determine the effect of alternative profiles on the source contribution estimates and on overall model performance. The ambient NMHC data were also examined by less complex tracer and bivariate regression methods to gain additional insights about probable source contributions, spatial and temporal patterns of emission sources, and photochemical reactions of various hydrocarbon species. NMHC was apportioned to motor vehicle exhaust, liquid fuel, gasoline vapor, gas leaks, architectural and industrial coatings, and biogenic emissions. Attribution of source contributions among the motor vehicle source categories is highly sensitive to the abundance of ethyne and light olefins to NMHC in the exhaust composition profile, which varies with emission control technology and vehicle maintenance and operation. 51 refs., 2 figs., 9 tabs.