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tionaJ Park. Ms. Thomas said about 15 percent of the year it is possible to see for 30 to 36 miles from the park. She said about 40 to 50 percent of the time one can see for 11 to 29 miles and 36 to 40 percent of the time 0 to 10 miles. She said that normal visibility should be 70 to 80 miles. Since 1948 visibility has gone down, particularly during the summer.
Ms. Thomas said that ozone was not as much of a problem in the park this past summer as it was in 1988. She said that the federal government considers ozone concentrations below 120 partB per billion safe, but about 20 percent of the population, especially those with bronchial problems and asthma sufferers, experience problems at 80 parts per billion. She said that 10 days this past summer ozone concentrations were above 80, compared to 50 days in 1988.
She Baid that in cities ozone is worse in late afternoon, but in the park it is worse in the middle of the night when it gets “blown in from the cities.”
Ms. Thomas noted that ozone puts stress on plants marking them with a “fine purple stipple.” She said plants stressed by ozone are more likely to succumb to other problems.
The third major environmental problem the park faces is acid rain, she said. She said the thin soils in the park have buffered as much acid as they can, and now are releasing it to the streams coming out of the park. “The streams will stay preSee
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