SIZE-SEGREGATED FINE PARTICLE MEASUREMENTS BY CHEMICAL-SPECIES AND THEIR IMPACT ON VISIBILITY IMPAIRMENT IN DENVER

In the winter of 1987-1988, a field study was undertaken to identify the principal causes of visibility impairment in Denver so that a plan to improve air quality could be designed. One focus of the field study was the measurement of the mass of sulfate, nitrate, organic and elemental carbon in particles as a function of particle size. The analysis of those measurements led to the following conclusions: (1) emissions of ammonia in areas northeast of Denver contribute to the mass of fine particle ammonium nitrate in Denver; (2) soot is much less efficient at scattering light than the other constituents of the Denver brown cloud, and much more efficient at absorbing light; (3) meteorological conditions that produce episodes of visibility impairment in Denver can be distinguished by the associated size distribution of airborne fine particles and (4) a significant fraction of the particle mass of organic carbon measured in the 1987-1988 Denver Brown Cloud Study could have been adsorbed gases.