On the nature of the diurnal variation of sulfates at rural sites in the Eastern United States

During the summer of 1976, sulfate samples were collected for 29 days at two rural sites in the Eastern U.S. other pollutant parameters, including ozone and sulfur dioxide levels, and meteorological factors such as temperature, humidity, and wind speed, were obtained. 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 ozone maximum. The second pattern, a nocturnal sulfate peak, occurred on calm nights when surface transport was not occurring, and was most pronounced on clear nights when ground fog developed.