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WEDNESDAY, July 9, 2003 (HealthDayNews) -- Country trees situated downwind of city pollution grow only half as well as the same kind of trees actually located in the city.
That curious finding comes courtesy of a Cornell University-based study in the July 10 issue of Nature.
"I know this sounds counterintuitive, but it's true. City-grown pollution -- and ozone in particular -- is tougher on country trees," study author Jillian W. Gregg says in a news release.
When she was a graduate student, Gregg began planting clones of cottonwood trees (also called poplars) in and around New York City. She also planted the cottonwoods in the Hudson River valley about 50 miles north of Manhattan.
She later harvested the cottonwoods and analyzed them. She found the biomass of the city trees was double that of the country trees. Gregg and her fellow researchers believe ozone is the main reason for this difference. Excess ozone at ground level interferes with the metabolism of trees and other plants.
The influence of atmospheric chemistry is the reason why the country trees in this study fared worse than their city cousins.
"Ozone is what we call a secondary pollutant. So while the primary precursors for ozone are emitted in the city, they must act in the presence of sunlight, over time, before ozone is formed. By then, the air mass has moved to rural environments," Gregg explains.
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