TRACKING OZONE - AIR-MASS TRAJECTORIES AND POLLUTANT SOURCE REGIONS INFLUENCING OZONE IN PENNSYLVANIA FORESTS

Ground-level ozone pollution is causing measurable damage to the forests of the eastern United States, including those in Pennsylvania's Allegheny Plateau region. This area is surrounded by many urban and industrial pollution sources in the Midwest, Southeast, and Northeast United States and in southeastern Canada. Any of these may play critical roles as source regions from which ozone and its precursor pollutants are carried toward the forests. This study identifies those geographic regions with the greatest potential influence on forest ozone concentrations via a climatological analysis of air-mass trajectories. In this analysis, observed meterological data and a trajectory model are used to calculate the spatial history of polluted air-masses. Multiple trajectories are examined using a newly adapted methodology of ensemble trajectory analysis in combination with ozone data and key synoptic weather patterns from a related climatology. Results indicate a critical region of influence centered on the junction of the Ohio and Mississippi River valleys, and extending eastward up the Ohio River Valley. These parts of Indiana, Ohio, Kentucky, Illinois, and Missouri have the greatest likelihood of influencing high-ozone air masses arriving in Pennsylvania, and they coincide with some of the highest emission regions in the country. In the worst cases, air masses accumulate pollutants for several days as they stagnate over this region, and then continue accumulating pollutants as they move slowly toward Pennsylvania. Brief comments regarding the research and policy implications of these results are provided.