Upper-Level Atmospheric Circulation Patterns and Ground-Level Ozone in the Atlanta Metropolitan Area

Abstract

Abstract The purpose of this paper is to identify middle-troposphere circulation patterns associated with high ozone concentrations during June–August of 2000–07 in the Atlanta, Georgia, metropolitan statistical area (MSA), which is located in the southeastern United States. The methods involved classifying daily 500-hPa geopotential height fields into synoptic types, determining the mean atmospheric conditions (i.e., daytime temperature, daytime relative humidity, daytime cloud cover, morning mixing height, and afternoon mixing height) for the types, determining the mean daily maximum 8-h average ozone concentrations for the types, and performing back-trajectory analyses for high-ozone types. There were a total of 12 synoptic types, and significantly high ozone concentrations across the MSA coincided with the three following types: Atlanta under a continental anticyclone, Atlanta to the east of a continental anticyclone and west of a trough, and Atlanta under the western side of a trough. The continental-anticyclone type was much more prevalent than the other two types. When the MSA was under or just to the east of a continental anticyclone, atmospheric conditions were conducive to increased in situ ozone production and pollutant carryover from the previous day. Between 45% and 60% of the days with those circulation patterns had ozone concentrations exceeding the federal standard. When the Atlanta MSA was under the western side of a trough, not only did the potential for in situ ozone production and pollutant carryover contribute to high ozone concentrations, but there also was a high potential for pollutant transport from the Ohio River valley into the Atlanta MSA.