Study: Smog emission from trees increasing rapidly

By Steven Schultz on July 13, 2004, 3:18 p.m.

Changes in U.S. forests caused by land use practices may have inadvertently worsened ozone pollution, according to a study led by Princeton University scientists.

The study examined a class of chemicals that are emitted as unburned fuel from automobile tailpipes and as vapors from industrial chemicals, but also come naturally from tree leaves. These chemicals, known collectively as VOCs, react with other pollutants to form ozone, a bluish, irritating and pungent gas that is a major form of smog in the lower atmosphere.

While clean-air laws have reduced the level of man-made VOCs (volatile organic compounds), the tree-produced varieties have increased dramatically in some parts of the country, the study found. The increase stems from intensified tree farming and other land use changes that have altered the mix of trees in the landscape, said Drew Purves, the lead author of the study that included scientists from four universities.

"There are seemingly natural but ultimately anthropogenic (human-caused) processes in the landscape that have had larger effects on VOC emissions than the deliberate legislated decreases," said Purves.

The full story is available in a news release.

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