Meteorological conditions are characterized for a prolonged period in which an air mass contained high concentrations of sulfate pollutants. The period occurred in the Los Angeles area from February 26 to March 5, 1975. In addition, the episode occurred during the off-season and virtually coincided with an oxidant episode. The meteorological conditions associated with both episodes were (a) slow moving air; (b) abundant sunshine; (c) elevated temperatures; (d) limited vertical mixing at the coast and inland vertical mixing varying from negligible at night to relatively deep in the daytime; (e) relatively very poor visibilities due to smoke, haze, and fog; and (f) high relative humidities at all times at the coast and at night at inland locations, but very low relative humidities in the daytime over inland locations. The ozone episode ended with the onset of strong winds and rain, while the sulfate episode persisted into the windy and wet period. Differences in the spatial patterns in sulfate and oxidant concentrations were observed and these are attributed to differences in the relative humidities at coastal and inland locations. Identification of these meteorological conditions provides information for air pollution investigators to use in attempting to forecast future sulfate episodes.

Includes bibliographical references (p. 18-20). PB-284 056. EPA-60074-78-022.