Historic polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) concentrations in Riverside, California: Evidence of a diffuse vehicular source

The goal of the research presented in this paper is to clarify the historic contribution of leaded gasoline combustion to ambient PCDD/F levels in Riverside, California during the initial period of leaded gasoline phaseout (1974–1980).; This goal was accomplished by analyzing seventeen archived hi-vol air filters from the Magnolia monitoring station in Riverside to determine ambient PCDD/F levels during the period 1974–1980. Ambient PCDD/F levels were correlated to ambient levels of vehicular pollutants (CO, NOx, Pb, TSP), and compared to modeled levels of PCDD/F that accounted for mobile sources in the greater Riverside urban area on the days of hi-vol filter collection.; Measured particle-phase PCDD/F levels (both uncorrected and corrected for vapor phase partitioning) were highly correlated to ambient vehicular pollutants, most notably CO and NOx, suggestive of a diffuse, vehicular source.; Back wind trajectories were utilized to determine which stationary sources were likely located upwind of the Magnolia site on days of hi-vol filter collection. Impacts of stationary combustion sources on downwind PCDD/F concentrations at the Magnolia site were examined qualitatively and compared to measured concentrations. The emission strength of upwind stationary sources did not correspond to measured PCDD/F concentrations at the Magnolia site; thus, stationary sources are not thought to have significantly influenced PCDD/F levels in the greater Riverside urban area.; A box model was utilized to predict PCDD/F concentrations due to vehicular sources. The box model reasonably described the variability of about 61% of measured PCDD/F and reasonably described the magnitude of about 50% of measured PCDD/F. The box model correctly predicted the variability of PCDD/F due to dilution, indicating the predominance of a diffuse source. Given the uncertainties in historic emission factors, activity, background concentrations, PCDD/F stability on 25+ year-old filters, and the unknown fate of PHDD/F in the environment, the box model provides plausible evidence of a vehicular contribution to ambient PCDD/F in the Riverside urban area during the period 1974–1980.; The results of the research suggest that vehicular sources were important in emitting and distributing PCDD/F throughout the environment in the past, especially in areas with few major stationary combustion sources.