Worried about air pollution? Your own backyard could be part of the problem! CSIRO and Monash University scientists have found that lawns and grasslands release vast quantities of pollutants into the air.
Firing up the mower and cutting the grass will just make things worse. Emissions of chemicals increase around 100-fold after grass is cut, taking hours to reduce to their original level.
To measure emissions of these air pollutants from grass, scientists from Monash and CSIRO set up a transparent chamber in a grass paddock in Gippsland, south-eastern Victoria. The scientists collected and analysed gases released by the grass over a two-year period. Their aim was to learn how emissions are affected by variations in temperature and light intensity, and by drought.
"It's not just cars and industry, or lawnmowers themselves, that cause air pollution," says Mr Ian Galbally, from the CSIRO Division of Atmospheric Research.
"Plants release highly reactive hydrocarbons that can add significantly to photochemical smog problems," Mr Galbally says. "The blue haze you often see over the Dandenongs in Victoria and in New South Wales' Blue Mountains is caused in part by the gases released by vegetation."
Wayne Kirstine from the Gippsland campus of Monash University conducted the research with Mr Galbally.
Although grasslands and pastures cover a quarter of the Earth's land surface, this study is one of the first of emissions from grass and clover.
"Emissions from grass are at their greatest in warm weather and at around midday, when sunlight is most intense," says Mr Galbally. 'No gases are released at night.'
"After we cut the grass in the chamber, gas release from clover rose by a factor of 80, and emissions from grass increased by 180 times," says Mr Galbally.
Cattle grazing or trampling will have a similar effect to mowing, increasing emission rates from grass.
Scientists believe that some of the additional gases released by cut grass are natural antibiotics, which act to disinfect the wound site.
Gases released by grass include the volatile organic compounds methanol, ethanol, propanone and butanone.
This study has shown that grasslands around the world may be one of the biggest sources of the gases methanol, and perhaps ethanol, in the atmosphere.