Long range transport of air pollution: a case study, August 1970

Abstract

An air pollution episode during August 1970 over the central United States is examined. By use of surface visibilities and an 850 mb wind trajectory analysis, the authors observed the pollution to advance as much as 700 mi from the central midwest (source region) into the upper midwest and Great Plains (impact area). A large, nearly stationary high pressure system over the source region allowed the pollution to accumulate beneath a midlevel subsidence inversion located generally near 700 mb. Southeasterly flow around the backside of the High and the northeasterly flow around a weak Low to the south advected the pollution into the impact area. At times, surface visibilities in parts of the impact area were restricted by haze to as little as 4 mi. Although particulate cound data were meager, several stations recorded their highest particulate count of the year during the episode.