US: Tree and industry gases a dangerous mix

American scientists are warning that gases emitted by plants can mix with
industrial pollution and create a very unhealthy aerosol.

The natural pollutant in question is isoprene, which is formed naturally in plants and animals and is a precursor of ozone. It is created by many deciduous trees, with oaks being the biggest polluters, and scientists say more than 500 teragrams is released annually worldwide (there are one billion kilograms in one teragram).

More isoprene is produced by plants and emitted into the atmosphere than all other gases, including those produced by human activities like burning gasoline and using industrial chemicals. Scientists admit that the reasons why plants are producing so much isoprene are not fully understood.

When the chemicals bump into acidic industrial air pollution, a reaction occurs creating tiny gluey droplets as aerosols - and that is unhealthy, warned researchers from the California Institute of Technology (Caltech) in the US who have been working with colleagues at the University of Copenhagen, Denmark, and the University of Otago, New Zealand.

"Particles in the atmosphere have been shown to impact human health, as they are small enough to penetrate deep into the lungs of people," said Caltech's Professor John Seinfeld.

Scientists expect the research will help inform the public and become a part of the criteria used to determine what kind of trees are planted in urban areas, to prevent further atmospheric pollution.