Mesoscale Meteorological Structure of a High-Ozone Episode during the 1995 NARSTO-Northeast Study

Observations and numerical model fields were analyzed to study the meteorological structures contributing to high concentrations of lower-tropospheric ozone over the northeastern United States on 14–15 July 1995. It was found that the episode is characteristic of high-ozone events associated with the Bermuda high, having light winds, high temperatures, few clouds, and sparse rain over the entire region. The specific distribution of ozone at the peak of the episode on 14 July is of particular interest, however, since only the area from the urban corridor to the Atlantic Coast experienced ozone exceedances of the National Ambient Air Quality Standard. The analyses showed that an Appalachian lee trough (APLT) played a vital role in this pattern. Mesoscale structures associated with the APLT that affected ozone formation and distribution included 1) south-southwesterly winds east of the trough, which favored accumulation of emissions in an airstream that passed directly along the urban corridor; 2) w...