Relationships between synoptic-scale atmospheric circulation and ozone concentrations in Metropolitan Pittsburgh,Pennsylvania

A synoptic climatology demonstrates the relationships between the atmospheric circulation and surface ozone (O₃) concentrations. To deduce these associations, a subjective synoptic classification scheme is applied to 10 years' O₃ data from the Pittsburgh metropolitan area. The results focus on four aspects of the atmospheric circulation-O₃ relationship: average, extreme-event, between season and year-to year conditions. On average, each of the nine circulation types is related to a characteristic O₃ concentration level and cumulative O₃ dose. Extreme high-O₃ events are associated with either the western side of a slowly migrating anticyclone or a stagnating extended high-pressure ridge; low-O₃ events are experienced under cool and cloudy cyclonic conditions. Between-season variations in the average and extreme circulation-O₃ relationshipsare observed: the high-pressure features that produce the high st O₃ levels in summer are related to low levels in winter, while circulation patterns that contribute very little to summertime O₃ build-up are associated with the highest levels of wintertime O₃. The latter situation could be caused by tropopause folding and the introduction of stratospheric ozone in winter months. While zonal (meridional) circulation regimes tend to produce lower (higher) mean annual O₃ levels, such year-to-year changes in synoptic-type frequencies do not appear to be strongly related to interannual variations in O₃, and other non-climatic factors appear to be of greater importance.