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  1. #1
    Join Date
    Jul 2001
    London, Britannia.

    Arrow 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)."

    Dangerous levels?

    Isoprene takes part in reactions that convert nitrogen oxide from car exhaust emissions into ozone.

    End extract <<

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  2. #2
    And if it gets really hot, the trees in UK may pollute as much as the rain forests in the Amazon?

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