An analysis of the meteorological parameters affecting ambient concentrations of acid aerosols in Uniontown, Pennsylvania

Ambient concentrations of aerosol strong acidity (H+) that were collected in Uniontown, Pennsylvania, during the summer of 1990 were evaluated to determine the relationships between meteorology and the magnitude of the H+ concentrations. An extensive database containing 17 meteorological parameters was compiled for the Uniontown - Pittsburgh region. The database included both surface and upper air meteorological parameters. Concentrations of ambient acid sulfate aerosols collected in Uniontown, Pennsylvania, in the summer of 1990 were greatly affected by both local and regional meteorological conditions. Seven distinct meteorological synoptic types or regimes were identified for the summer months. A clear association was shown between episodic events of elevated ambient H+ concentrations and one of the regimes, referred to here as synoptic type 5, which occurred when an anticyclone set up to the east of the mid-Atlantic states. Much of the variability (approximately 45%) in H+ concentrations for the overall model was explained by the surface air temperature. Approximately 10% of the Hʹ variability was explained by westerly winds as expressed by the U components of the morning 850 mb wind and the mean daily surface wind at Uniontown. Results showed that for days under the influence of synoptic type 5, which was associated with the highest levels of ambient Hʹ, the surface temperature explained approximately one-third of the variability in Hʹ concentrations. The height of the mixing layer also affected the variability in H+ concentrations, accounting for nearly a quarter of the variance. These results show that an analysis of the surface wind speed and direction alone will not adequately explain the variability in the concentrations of ambient acid aerosols. Analyses of the meteorological parameters affecting ambient concentrations of acid aerosols should include the mixing height, as well as the temperature, wind speed, and wind direction; both at the surface and for an upper level of the atmosphere that facilitates regional transport of pollutants.