WASHINGTON (AP) — That sweet scent of a freshly mowed lawn may really be the smell of air pollution.
Scientists studying the sources of chemicals in the air have found that injured grass gives off volatile compounds.
"Wounding, cutting and drying of leaves and stems occur both naturally and by human activities, wound-induced and drying-induced ... compounds are expected to be significant in the atmosphere," a team of researchers says in a study scheduled to appear in a future issue of the journal Geophysical Research Letters.
"In urban areas, lawn mowing may contribute to the total ... emissions and impact air quality," the report says.
But do not panic. While total emissions from cutting grass and crops worldwide may seem large, it does not mean cutting the grass is dangerous for individuals.
"It just doesn't seem likely to me that the smell of newly mown grass is toxic," said Ray Fall of the University of Colorado, a biochemist and one of the researchers.
"Mowing the lawn is no more hazardous than eating raw vegetables," he added, pointing out that chewing veggies also releases tiny amounts of the same chemicals.
Even the grazing of animals can release these compounds into the air, he said: "Every time a cow chomps grass you get these little surges."
Yet, Fall said the team was surprised at the variety of chemicals released when crops were cut and during the drying process, including methanol, hexanal, acetaldehyde, acetone and butatone. Some, such as acetone, can contribute to the formation smog, the paper notes.
The scientists estimate that cutting crops adds about 1.6 million tons of acetone to the atmosphere annually, compared with estimated total natural emissions of eight to 13 million tons. They have not estimated the totals for other compounds.
The researchers studied red fescue grass cut from a lawn near their laboratory in Boulder, Colo., and clover grown in a greenhouse. This summer they plan a study of alfalfa.
The Environmental Protection Agency has a laboratory in North Carolina looking at biological emissions of chemicals, but has not studied grass or clover.
The new report says that in addition to lawn mowing, chemicals are given off by drying plant material in arid areas and during the harvest in agricultural areas.
"It can be expected that the resulting emissions have a significant impact on the chemistry of the atmosphere over these areas," said the report.
"Cut and drying organic material appears to be a significant global, and possibly regional, source of volatile organic compounds. One that we think may not have been well accounted for before," Carlton J. Howard of the National Oceanic and Atmospheric Administration's Aeronomy Laboratory in Boulder said in a telephone interview.
Howard noted that emissions from lawn mowers and even barbecues have been identified as components of pollution in some urban areas and this study adds one more source of chemicals.
"It is something that needs to be looked at carefully," he said.
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