Influence of particulate size on statistical studies of visibility at California regions

NEHZAT MOTALLEBI, THOMAS A. CAHILL, ROBERT G. FLOCCHINI

Abstract

A multiple linear regression analysis of particulate, gas, and meteorological data is presented for different sites in California. The results of the regression analysis provide some insight into visibility -impairing processes. One remarkable factor is little or no association between visibility and the abundant sulfur component with diameter less than 0.65 µm. One must conclude that it was the growth of particles above 0.65 µm that caused the poor visibility; growth that was favored by the higher humidities but that may also reflect the ultimate sources of the sulfur. This study has shown the key role played by particulate size in atmospheric extinction. Those conditions that encourage the formation or growth of particles in the optically effective part of the accumulation mode are linked to reduced visibility. These results are in good agreement with Mie theory, and allow a much better match between theory and experiments than those gained by summing all mass below 2.5 µm or even key chemical constituents in the less than 2.5 µm regime.

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