ATLANTA -- The federal Environmental Protection Agency says it has determined that trees in Atlanta and other cities are partly responsible for air pollution, reversing its earlier doubts that trees contributed to smog.
As a result, EPA officials said Thursday, Atlanta may have to alter its strategy for combating air pollution by imposing new controls on auto exhausts and industrial emissions.
EPA officials denied the shift in policy constitutes an endorsement of the 'killer tree' theory during the early 1980s stewardship of Interior Secretary James Watt that claimed tree emissions were a direct cause of urban air pollution.
But the said studies in Atlanta by Georgia Tech researchers show trees sometimes produce large quantities of hydrocarbons, key ingredients in the formation of ground-level ozone.
In the presence of sunlight, hydrocarbons react with nitrogen oxides, which come primarily from auto exhausts, to form ozone, an irritating gas that impairs breathing and irritates heart and lung problems.
Atlanta's air violated federal standards for ozone at least 18 times last year -- despite 10 years of increasingly stringent and costly controls in the five-county metropolitan Atlanta area.
'This may explain why in Atlanta they have reduced hydrocarbons and have not seen the kind of response we would have expected,' Gerald Emison, director of the EPA's office of air quality planning and standards, said at a news conference in Washington.
'Tree emissionsare more important than we thought,' he said. 'In the past we have probably underestimated what we need to control ozone.'
Emison said the new understanding to trees' role in air pollution clears the way for other cities to take 'natural' hydrocarbon emissions into account in their air pollution control plans.
Emison said early evidence suggests Atlanta's hydrocarbon levels are unusually high because if its many oak trees, which emit an especially reactive hydrocarbon called isoprene. Preliminary surveys show the levels of natural hydrocarbons in Houston, Philadelphia, Baltimore and Pittsburgh are less than half of those in Atlanta.