Comparison of Predicted and Observed Solar Radiation in an Urban Area

Abstract

Measurements of the downward solar radiant flux in the St. Louis, Mo., area are compared with predictionsfrom an approximate solution to the radiative transfer equation. The atmospheric aerosols were assumedto have a power size distribution, dn/dr∼r-4, and the refractive indices suggested by Fischer (1973) foran urban area. On a relatively clean day, the predictions compared well with observations. On a hazy day,the comparison was poor with the a priori choice of aerosol properties. The particles on the hazy day apparently had more submicron particles than those found in the assumed size distribution, and the particleswere considerably less absorbing than those observed by Fischer. These changes could represent the effectsof relative humidity and different air mass characteristics.