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Do trees pollute? In the early 1980s, then-president Ronald Reagan and some noted scientists
attracted attention when they confirmed that trees themselves are a possible source of some types of air pollution. Trees do contribute to the formation of ozone by releasing VOCs such as
isoprene, monoterpene, and alpha-pinene.
Under Title 1 of the federal Clean Air Act, states are required to estimate how much trees and plants
contribute to VOC production for those areas that exceed ozone standards. The sources of these VOCs, known collectively as "biogenics," include forests, crops, lawn grasses, and other
vegetation. The more vegetation an area has, the more these biogenics will contribute to overall VOC levels. For example, biogenics are estimated to account for 22 percent of all VOCs emitted
in the woody Houston-Galveston area, but only 12 percent in the arid El Paso area. Nationally, the EPA estimates that biogenics and other natural sources actually produce more emissions of
VOCs than do anthropogenic sources. Of course, biogenic sources are natural sources of air pollution, and cutting down trees to reduce pollution would be counterproductive: the air quality
benefits of biogenics far outweigh the costs, since plants produce oxygen, filter the air, and prevent erosion. Biogenic sources are not figured into the calculation of how much an area must
reduce VOC emissions.
(Sources: TNRCC, Revisions to the State Implementation Plan for the Control of Ozone Air Pollution [May 13,
1994]; EPA, Regulatory Impact Analysis of New Ozone and Particulate Matter NAAQS Standards [July 17, 1997].)
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