Ambient concentrations of sulfur dioxide (SO₂) were measured near a coal-fired power plant in central Pennsylvania. Coal-fired power plants are the primary anthropogenic source of SO₂ in the United States. Areas downwind of power plants that are exposed to the emission plume experience much higher SO₂ concentrations than surrounding areas. SO₂ is a harmful pollutant that can affect respiratory function when found in high concentrations and can create regional visibility and acid deposition problems. Measuring downwind concentrations and modeling plume dispersion allows the areas most affected by the power plant SO₂ emissions to be determined.

Background and downwind SO₂ concentrations were measured with a pulsed fluorescence ambient SO₂ analyzer located 6 km away from the Sunbury Generation power plant in Snyder County, PA. Elevated SO₂ concentrations were recorded whenever the monitor was downwind of the power plant, as determined from prevailing winds. A computer-based dispersion model was then used to predict SO₂ concentrations for the periods when the plume affected the monitor site. Using appropriate stability class, wind speed, and emission data, the model provided predictions of downwind and crosswind concentrations. By comparing the measured and modeled concentrations, it was possible to assess the ability of the model to accurately represent the dispersion process.