EXAMINING THE RELATIONSHIP AMONG ATMOSPHERIC AEROSOLS AND LIGHT-SCATTERING AND EXTINCTION IN THE GRAND-CANYON AREA

During the winter and summer months of 1990 a special study called Pro ject MOHAVE (measurement of haze and visual effects) was carried out w ith the principle objective of attributing aerosol species to extincti on and scattering and the aerosol species to sources and/or source reg ions. The study area included much of southern California and Nevada, Arizona, and Utah; however, the intensive monitoring sites and primary focus of the study was on the Colorado Plateau of northern Arizona, s outhern Nevada, and Utah. This paper reports on the apportionment of v arious aerosol species to measured fine and coarse mass concentrations and these species to scattering and extinction. The study is unique i n that a number of ''ambient'' integrating nephelometers were operated to measure the ambient scattering coefficient, while transmissometers were used to measure atmospheric extinction. Comparison of measured s cattering, extinction, and aerosol species concentration, both statist ically and theoretically, allows for an estimate of scattering and abs orption efficiencies. Analysis suggests that using elemental carbon, d erived from thermal optical techniques, to estimate absorption may sig nificantly underestimate absorption. Using elemental carbon, absorptio n is estimated to be 5% of extinction, while direct measurements of ab sorption suggest that it is about 30% of measured extinction. Furtherm ore, because light absorption by soil is usually not accounted for, so il extinction is underestimated by about 30%.