Spending an hour behind a roaring lawn mower can spew nearly the same amount of oily pollution into the air as a 100-mile car trip, according to a Swedish study.
The study, which researchers say is the first to compare the pollution of the average car and lawn mower, recommends that catalytic converters be added to the millions of U.S. mowers sold each year to reduce the amount of pollution they cause. The report appears in the June issue of Environmental Science and Technology, the journal of the American Chemical Society.
Outfitted on cars since the 1970s, catalytic converters transform a large portion of car exhaust into harmless compounds. But they aren't required on lawn mowers and similar equipment, which the Environmental Protection Agency says is responsible for about 10 percent of the pollution from "mobile sources," which includes trucks and cars.
"Lawn and garden equipment really does add to air pollution," says Cathy Milbourn, spokeswoman for the EPA. "People can reduce the impact it has by using [lawn equipment] in the early morning or in the late afternoon. Or perhaps not at all" on high ozone days, she says.
Scientists say sunlight and heat, stronger during midday, contribute to the creation of ground-level ozone, the principle component of smog.
Milbourn says the EPA recognizes the contribution garden equipment makes to air pollution, but instead of making catalytic converters mandatory, the agency has tightened emission rules.
"We say to the manufacturers, here are the emission standards you need to reach, and we let the manufacturers decide how to do it," she says.
In 1999, the EPA finalized new exhaust standards for small machines like lawn mowers and weed whackers, which will be fully phased in by 2007. The new standards call for a 59 percent reduction in hydrocarbons.
Americans use an estimated 38 million lawn mowers to trim their lawns, according to the Outdoor Power Equipment Institute, a group that represents the manufacturers of lawn care machinery. But that number doesn't include the millions of snow blowers, trimmers, leaf blowers, tillers, chain saws and other small garden and lawn contraptions. By some estimates, nearly 100 million such machines are in use.
The main agents found in engine exhaust are compounds known as hydrocarbons, which help ground-level ozone form. Ground-level ozone is a particular problem in cities during the sultry summer months, when heat, sunlight and pollution combine in a potent mix. High levels of ground-level ozone exacerbate asthma and other lung problems, and can even cause respiratory problems in otherwise healthy people.
Roger Westerholm, a chemistry professor at Stockholm University in Sweden and author of the lawn mower study, says instituting the use of catalytic converters could cut down on one particularly dangerous hydrocarbon pollutant by up to 80 percent.
"Using a catalyst would help prevent most emissions from small engines," he said in a statement. "Of course, people could also use an electrical-powered lawn mower instead."
But the Outdoor Power Equipment Institute claims the use of catalytic converters is impractical for small machines like mowers. The group estimates that the average mower only gets 25 hours of use per year, burning perhaps a few gallons of fuel.
"From a consumer standpoint, catalytic converters would probably make the cost of a mower very, very high," says Peggy Douglas, spokeswoman for the group.
Electric-powered machines aren't very practical for many consumers either, she says.
"I have a small, battery-powered mulching mower, which is perfect for my small yard," says Douglas. "But for people who have something like a one-acre yard or more, the technology just isn't there yet."