Solar irradiation and atmospheric pollution

Abstract

This report contains the results from 30-minute observations of UV (0.29 to 0.38 μm) and total solar irradiation, (0.3 to 3.0 μm) made on the rooftop of a medium size building in downtown Cincinnati. The one year data are obtained from a pyranometer and a UV radiometer used in conjunction with integrators and printout devices. UV and total direct solar irradiation data are analyzed in order to detect possible weekly pollution cycles. It is found that the average difference between weekday and Sunday values in Cincinnati is 3.6% and 29.2% for total direct and UV irradiation, respectively. Chi-square tests indicate significance of these differences at the 5% and 0.5% levels. Ratios of UV and total solar irradiation are presented as indices of atmospheric opacity and compared with turbidity coefficients. It is shown that the ratios vary relatively little irrespective of whether the atmosphere seems to be polluted or clean. Apparently the particle size distribution in a polluted atmosphere is no different from that in clean air. It is suggested that the small decrease in the ratio of UV to total solar irradiation for a polluted atmosphere may be due to selective absorption by gaseous pollutants. UV irradiation curves are used to analyze processes leading to fumigation and photochemical smog formation. Calculation of theoretical UV irradiation curves allows the exact assessment of the magnitude of UV attenuation due to pollutants. This attenuation ranges from 30% in clean to over 80% in smoggy atmospheres.