WHILE we are yet to ascertain whether
aerosols are warming or cooling our
planet, a scientific team has traced a new
source: deciduous trees. These are
plants that shed their leaves seasonally.
So far aerosols were described as particles
of pollutants like sulphur dioxide,
black carbon (soot) and sea salt that
remain suspended in the air.
Deciduous plants release around 500 teragrammes (1 teragramme equals 1012 grammes) of carbon each year in the form of an organic compound called isoprene (hydrocarbon). The chemistry of what happens to the compound as it forms aerosol particles has, so far, been unclear.
The team from CalTech in the US, University of Otago in the New Zealand and University of Copenhagen, in Denmark, found isoprene is repeatedly oxidized in the atmosphere to form an epoxide, hitherto unknown, called dihydroxyepoxide.
Epoxides are generally synthesized in the chemicals industry. It is rare to find such huge quantities of an epoxide, produced naturally by plants. "Nothing is known about its fate in the atmosphere. Given the tendency of this epoxide to stick to acidic particles, it is likely to form aerosols under pristine conditions," said Fabien Paulot of CalTech.
Paul Weinberg, atmospheric science professor from the same insitute, said: "If you mix emissions from the city with emissions from plants, they interact to alter the chemistry of the atmosphere." Higher the concentration of aerosols, human-induced or otherwise, foggier is the visibility in that area. Tadeusz Kleindienst, scientist at the US Environmental Protection Agency, said that air quality regulatory agencies mainly pay attention to the effect of emissions from cars and industries; less is known about biogenic emissions. Hence their visibility predictions as well as other climatic predictions are not that accurate.
This study published in the August 8 issue of Science explains from where the Great Smoky Mountains derive their name: the mountains are covered by one of the largest patches of deciduous forests in North America.
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