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| ?? | ?? | The graph shows a rising trend in ozone levels at Big Bend, Great Smoky Mountains, and Shenandoah National Parks from 1989 to 1998. When confronted with data documenting deteriorating air quality, NPS managers are using a variety of strategies to exercise influence over air pollution sources the National Park Service cannot control. |  |
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This material is from Natural Resource Year in Review--1999; published by the National Park Service, U.S. Department of the Interior, August 2000 (publication D-1406) /YearInReview/yir/yir99/pages/02challenges/03shaver_graph.htm |
