A Study of Summer Midday Low-Visibility Events in the Los Angeles Area

Citation

Larson, Susan Mary (1988) A Study of Summer Midday Low-Visibility Events in the Los Angeles Area. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/33vc-mc45. https://resolver.caltech.edu/CaltechETD:etd-11072007-152224

Abstract

The reduction of visibility due to air pollutants in the Los Angeles atmosphere can be severe. During summer midday periods, visibility can be reduced to less than a few kilometers. A five-site air monitoring network operated during the summer of 1984 provided data needed to characterize the summer midday visibility problem in the Los Angeles area. Light scattering and absorption by fine aerosol particles was found to account for more than 80% of the light extinction at the five sites studied. Carbonaceous aerosols and sulfates were responsible for approximately half of that fine aerosol burden. The theories of light scattering and absorption, and the data collected describing the physical and chemical characteristics of the suspended particulate matter and gaseous pollutants were used to calculate the light scattering coefficient and extinction coefficent present on each experiment day. The theoretically computed scattering and extinction coefficients are in reasonable agreement with measurements of those quantities.

One method of presenting the results of a visibility model in a readily understood fashion is to produce synthetic photographs that simulate the appearance of the scene of interest in the presence of a specified level of air pollution. A procedure for creating such synthetic photographs is developed, and methods for testing the accuracy of image processing-based visibility models are explored. The contrast reduction observed when objects are viewed through a polluted atmosphere is reproduced in the synthetic photographs, and with the inclusion of a radiative transfer code to calculate sky intensities, the appearance of the sky can be accurately simulated.

Since carbonaceous aerosol is the largest single contributor to fine particle concentrations in the Los Angeles atmosphere, pollutant abatement programs directed at visibility improvement must consider the reduction of primary carbon particle concentrations. The effects on visibility of strategies that have been proposed for reducing the emissions of primary carbon particles are examined. It is estimated that the mean light extinction coefficient in the Los Angeles area atmosphere could be reduced by 8% to 15% by means of carbon particle emission controls costing $80.4 x 10⁶ year⁻¹. Controls on other emissions would further improve local visibility.

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