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Abstract
Size-segregated impactor samples of Denver’s wintertime airborne particulate were analyzed for the major chemical species. These species are responsible for most of the pollution-related visibility reduction in Denver. Samples were collected three times a day during a 40-day field program in November-December, 1978. Each of the measured chemical species (sulfate, nitrate, ammonium, bromide, organic and elemental carbon) had a log-normally distributed accumulation mode with a mass median aerodynamic diameter near 0.3 μm. For all species, particle size increased with increasing relative humidity. These results are supported by electrical aerosol analyzer (EAA) measurements. The impactor results for this time period are consistent with a photochemical mechanism for particulate nitrate formation and a heterogeneous mechanism for the formation of sulfate particles.