Modeling of Indoor and Outdoor Exposures and Risk from Outdoor Benzene Emissions in Los Angeles

This paper reports on a demonstration study of the use of dispersion and exposure modeling to estimate carcinogenic risk to residents of the South Coast Air Quality Management District from benzene emitted into the atmosphere from outdoor sources. Exposures in indoor and outdoor environments are estimated throughout the basin. The distribution of individual risks across the population and among various population subgroups is assessed. The resulting expected excess lifetime cancer incidence is also evaluated. The fractions of overall risk attributable to various emission source types are compared. The results show that the contribution to overall carcinogenic risk from outdoor benzene emissions is split approximately equally between mobile sources (such as vehicles) and small, dispersed sources (for example, gasoline stations). The contribution of industrial sources (such as, large stationary sources) is negligible in comparison.