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

Abstract

A synoptic climatology demonstrates the relationships between the atmospheric circulation and surface ozone (O 3) concentrations. To deduce these associations, a subjective synoptic classification scheme is applied to 10 years' O 3 data from the Pittsburgh metropolitan area. The results focus on four aspects of the atmospheric circulation-O 3 relationship: average, extreme-event, between season and year-to year conditions. On average, each of the nine circulation types is related to a characteristic O 3 concentration level and cumulative O 3 dose. Extreme high-O 3 events are associated with either the western side of a slowly migrating anticyclone or a stagnating extended high-pressure ridge; low-O 3 events are experienced under cool and cloudy cyclonic conditions. Between-season variations in the average and extreme circulation-O 3 relationshipsare observed: the high-pressure features that produce the high st O 3 levels in summer are related to low levels in winter, while circulation patterns that contribute very little to summertime O 3 build-up are associated with the highest levels of wintertime O 3. 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 O 3 levels, such year-to-year changes in synoptic-type frequencies do not appear to be strongly related to interannual variations in O 3, and other non-climatic factors appear to be of greater importance.