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Shenandoah National Park officials continue to be concerned about the high ozone pollution levels that the Park has been experiencing during the summer of 1993. Since the beginning of the year the Park has had 21 days when ozone pollution levels were above 80 parts per billion (ppb). Superintendent Bill Wade said “We are concerned when ozone gets about 80 ppb because sensitive plants begin to show symptoms of injury, and some people who are sensitive to ozone begin to experience health problems.”
Ozone pollution levels were high in July on six separate days. The air quality monitoring stations at Big Meadows and/or Sawmill Run had levels above 80 ppb on those days with the highest reading of 105 ppb on July 28. Air quality monitoring specialist Rolf Gubler stated, “As of early Sept. 1993, the Park has had over three times as many high ozone pollution days than the entire summer of 1992.” Ozone pollution levels must exceed l!20 ppb (unhealthy levels) in order to violate the federal health standard established by the Environmental Protection Agency. The last time the Park experienced unhealthy ozone pollution levels was in 1988 on two separate days.
At ozone pollution levels of 80 ppb to- higher, persons who are sensitive may experience symptoms of breathing difficulty, a burning sensation in the chest or throat, dizziness, weakness, and headaches. Ozone is equally toxic to sensitive species of trees including white pine, tulip poplar and black cherry. Ozone enters pores in the leaves (stomates) and kills chloroplast cells, decreasing the tree’s ability to produce its own food.
Ozone exists naturally in a thin layer in the upper atmosphere (stratosphere) where it helps screen out much of the harmful sunlight that can cause skin cancer and leukemia. When formed in the lower atmosphere however, ozone is a highly toxic gas that can affect human health and cause injury to vegetation. This type of ozone formation is caused primarily by a chemical process between several types of air pollution given off by
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