Analysis of Urban-Rural Solar Radiation Data from St. Louis, Missouri

Abstract

The results of an analysis of simultaneous measurements of incident solar radiation from six locations in metropolitan St. Louis, Missouri are described. The measurements were taken continuously from September 1975 through March 1977 with pyranometers with all-wave and 395 and 695 nm cutoff filters. This report documents typical urban-rural variations of incident solar radiation. Atmospheric pollutants over the center of metropolitan St. Louis reduced incident all-wave solar irradiation by ?3%. Under cloudless conditions, differences between urban and rural irradiation were ?4.5% during winter and 2% in summer. At two suburban sites, the irradiation depletion averaged 1 and 2% for summer and winter seasons, respectively. Under all conditions, the ratios between stations for the complete experiment were similar to those for cloud-free conditions. Although the comparisons were stratified by wind direction and speed, visibility, time of day and day of the week, only wind direction had a significant effect on the interstation ratios. For cloudless days two suburban sites and a rural site north of the city received ?3.5% less radiation (compared to a control site) with south than north winds. Wind direction had an effect because pollutants were advected from major sources near the city center. The two urban sites exhibited only ?1% change due to north-south wind differences. The interstation comparisons for all days were also partitioned by wind direction. With north winds, the suburban and northern rural sites showed ?2?3% more irradiation (compared to a control site south of the city) on all days than on cloudless days for both the summer period and the complete experiment.