Air pollution and meteorology was studied over a dammed portion of the Susquehanna River – Lake Clarke - during the time period of June through August 2007 to assess the influence that recreational watercraft have on the air quality over a man-made lake and the surrounding lake-shore population. The site area is located at Long Level, York County, approximately 8.5 km upriver from the PPL Safe Harbor hydroelectric power plant in south central Pennsylvania. The topography of the area near Long Level is one of steep slopes along both river banks, which is conducive to the funneling of transported air pollutants from the surrounding region, and trapping of pollutants emitted by watercraft operating on the lake. The static stability found naturally in the near-surface layer over a cooler water surface, especially in summer, was hypothesized to only exacerbate air quality issues. This study focused on: 1) measurements of criteria pollutants along the lake-shore, 2) comparison of these data with regional concentrations obtained from the PA Department of Environmental Protection (DEP) monitoring sites in Lancaster and York, 3) characterization of the meteorological condition on multiple scales ranging from local to synoptic, and 4) and diagnosis of the meteorological forcing mechanisms using WRF simulations.

On-site measurements of criteria air pollutants, O3, CO, NOx, and SO2, were continuously recorded by instruments located inside a trailer that was situated about 20 meters from the west bank of Lake Clarke at Long Level. In addition, total and back-scattering coefficients were obtained using a three-wavelength nephelometer. These data were compared to the DEP measurements of criteria pollutants and particulate matter (PM) for York and Lancaster Pennsylvania. Both DEP monitoring sites are located near the urban centers of their respective cities, so this would represent the worst-case scenario for proximity measurements. Basic meteorological data were collected at the trailer, and at the Frey Farm Landfill, which is located on the opposite side of the river from Long Level (east side) and at an elevation of 138 meters above lake level (207.3 meters above sea level). Meteorological data were also collected at the DEP sites and from Millersville University, approximately 8 km east of Long Level. Atmospheric profiles using a tethered balloon are planned for August to document the conventional meteorological variables and atmospheric stability over the lake.

Preliminary results indicate that O3 concentrations were often very similar for the three sites when meteorological conditions were near the climatological norms. However, there were a few select periods, when the area was under the influence of a sub-tropical air mass and air temperatures exceeded 30 C, when O3 concentrations at Long Level peaked higher than the surroundings, and remained consistently higher throughout the corresponding nighttime hours. During these time periods, O3 concentrations at the DEP sites possessed a greater diurnal variation compared to the Long Level site. The higher nightly concentration of O3 at Long Level, while not at dangerous levels, nonetheless subjects people who live next to the river to a greater long term health risks.

We hypothesize that the nightly elevated O3 concentrations at Long Level are due to local emissions from York and Lancaster that drain into the Susquehanna River Basin after the near surface air begins to cool and stabilize around sunset. This high static stability when combined with the local topography tends to trap air pollutants in the near-surface layer above the lake. During the daytime, the local emissions from the power boats and cars cause greater peak O3 concentrations at Long Level than at the DEP sites, which are located over land and where the atmosphere experiences greater mixing and ventilation of emissions.

Data analysis will continue through August and into the waning days of solar summer. Measurements obtained using a tethered balloon will provide detailed vertical profiles of meteorological variables and ozone. At the time of abstract submission, this data is not yet available. More complete results will be presented via poster format at the Conference.