Science News :: Heatwaves can cause trees & other vegetation TO POLLUTE its reporte
Article extract >>
Trees are supposed to be one of nature's greatest defences against pollution, but new data suggests they can sometimes have the opposite effect.
Conventional wisdom holds that plants will purify the air, helping to reduce concentrations of harmful gases.
But experts at York University now say this effect can reverse itself in the UK during extremely hot conditions.
When temperatures exceed a threshold, trees and other plants emit chemicals that encourage toxic ozone production.
As the temperature increases, the emission rate increases almost exponentially
Dr Alastair Lewis, York University
The discovery was made when the team measured ozone levels in Chelmsford, Essex, during two weeks of last year's summer heatwave.
When temperatures rose above about 35C, deciduous trees began emitting greatly increased amounts of the compound isoprene. This is usually produced only in relatively small amounts.
"At 25C, the amount of [isoprene] emissions from the average UK deciduous tree is pretty low. But as the temperature increases, the emission rate increases almost exponentially," York team leader Dr Alastair Lewis told BBC News Online.
"At 30C, it's starting to become important. By 35C, the emission rate has gone up by maybe an order of magnitude (10 times)."
Isoprene takes part in reactions that convert nitrogen oxide from car exhaust emissions into ozone.
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For more inf :: http://news.bbc.co.uk/2/hi/science/nature/3700565.stm
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