Visibility-reducing species in the denver “brown cloud”—II. Sources and temporal patterns

Abstract

The chemical and optical measurements collected at the General Motors Research Laboratories' site during the 1978 Denver “brown cloud” study are combined with data on energy consumption and emissions, as well as the use of tracer techniques, to estimate the contributions of the various sources to the fine paniculate mass (FPM) and the visual range reduction (VRR). Although no single source dominates either the FPM or the VRR, combustion processes account for over 80% of both. The major contributors to both the FPM and VRR are: motor vehicles, 26 and 27% (diesel trucks, 8 and 12%; light-duty noncatalyst vehicles. 14 and 9%; light-duty catalyst-equipped vehicles, 4 and 5% and tire rubber, negligible and 1%), coal combustion, > 20 and > 25%, and wood burning, 12 and 18%. The remainders of the FPM and VRR are due chiefly to fuel oil and natural-gas combustion and crustal and fly ash material. The motor vehicles and the wood combustion are the principal sources of both elemental and organic carbon particles while the coal combustion is the most important source of paniculate sulfate and nitrate precursors. Essentially, all the carbonaceous particles appear to be primary particles while most of the sulfate appears to be produced by a heterogeneous process. Both heterogeneous and homogeneous (photochemical) mechanisms appear to be producing nitrate, with the photochemical one being more important.