Synoptic controls on summertime surface ozone in the northeastern United States

Abstract

The relationship between synoptic-scale circulation patterns and surface ozone (O 3) across the northeastern United States was investigated for summers 2000-2004. Observational data consisted of 1200 UT sea level pressure fields obtained from the National Centers for Environmental Prediction Global Final Analysis and O 3 measurements from 474 Environmental Protection Agency and five AIRMAP monitoring sites. The five most common circulation patterns, or map types (I-V), were identified with a correlation-based synoptic categorization technique, which persisted on 65% of the days during the study period. Map type I, characterized by stagnant warm conditions throughout the northeast, occurred most frequently (21%) with associated episodes of high O 3. Interannual variability in O 3 varied regionally from a seasonally averaged daily maximum value of 64 ppbv in 2002 to a minimum of 52 ppbv in 2004. By considering both the sea level pressure system intensity and frequency of each map type, 46% of the interannual variability in summertime O 3 was reproduced with intensity being the dominant factor. The remaining interannual variability was possibly due to nonlinear relationships between climate and biogenic emissions and/or recent reductions of power plant emissions of nitrogen oxides (NO x) over the eastern United States. The storm track of cyclones in the eastern United States was a key determinate of the intensity of circulation patterns. Copyright 2007 by the American Geophysical Union.