24 April 1998

Grass No Longer Green

People who ignore warnings to "Keep Off The Grass" may be contributing to global warming. That's because lawns and grasslands release vast quantities of pollutants into the atmosphere, say a team of Australian scientists - and the more you tread, the greater the emissions.

The findings could change the way we see parks and gardens. That plush lawn you mow every Saturday is in fact a photochemical smog factory, pumping out such volatile organic compounds as ethanol, propanone and butanone. Grasslands around the world - covering a quarter of the earth's land surface - are also a major source of methanol.

"It's not just cars and industry, or lawnmowers themselves, that cause air pollution," says Ian Galbally of the Commonwealth Scientific and Industrial Research Organization. "Plants release highly reactive hydrocarbons that can add significantly to photochemical smog problems. The blue haze you often see over the Dandenongs in Victoria and in the New South Wales' Blue Mountains is caused in part by the gases released by vegetation."

But it gets worse. Trampling and mowing can increase chemical emissions more than one-hundred fold, say the researchers. In one of the first studies of its kind, scientists from the CSIRO and Monash University set up a transparent chamber in a field in Victoria, collecting and analysing gases released from grass and clover over a two year period. "After we cut the grass in the chamber, gas released from clover rose by a factor of 80, and emissions from grass increased 180 times," says Galbally.