NATURE OF THE DIURNAL-VARIATION OF SULFATES AT RURAL SITES IN THE EASTERN-UNITED-STATES

During the summer of 1976, the General Motors Research Laboratories' mobile atmospheric research laboratory collected 4-h sulfate samples for 29 days at two rural sites in the Eastern United States. In addition, simultaneous measurements of other pollutant parameters including O3, SO2, and bscat, and meteorological parameters including temperature, relative humidity, wind speed and direction, ultraviolet intensity, and inversion height were obtained. The results indicate that the sulfate levels are governed by meteorology rather than local sulfur sources. Two types of distinct diurnal patterns were observed. In the first type, a peak was observed in mid-afternoon at about the time of the O3 maximum. Data presented in the text, however, indicate that photochemistry by itself cannot account for the sulfate peak. Afternoon vertical mixing of sulfates transported above the nocturnal inversion layer appears to play a significant role. The second type of diurnal pattern, a nocturnal sulfate peak, occurred on calm nights when surface transport was not occurring and it was most pronounced on clear nights when ground fog developed. The data suggest that the 03-S02-olefin reaction mechanism is significant on nonfoggy nights and the O3-S02-fog droplet mechanism is important on foggy nights. © 1979, American Chemical Society. All rights reserved.