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Grass Cutting Beats Driving in Making Air Pollution

ENS 31may01

STOCKHOLM, Sweden  --  The air pollution from cutting grass for an hour with a gasoline powered lawn mower is about the same as that from a 100 mile automobile ride, according to a new study from Sweden. The report, which the authors say is the first to compare lawn mower pollution with auto mileage, recommends using catalytic converters on mowers.

One old gas powered lawn mower running for an hour emits as much pollution as driving 650 miles in a 1992 model automobileOne old gas powered lawn mower running for an hour emits as much pollution as driving 650 miles in a 1992 model automobile (Photo courtesy U.S. Environmental Protection Agency)

One problematic pollutant from mowers is polycyclic aromatic hydrocarbons, or PAHs, said Roger Westerholm, Ph.D., an assistant professor in the department of analytical chemistry at Stockholm University. Westerholm claims that such emissions, similar for both riding and push mowers, can be cut by more than 80 percent using a catalytic converter like those used in automobiles.

The 20,000,000 small engines sold in the U.S. each year contribute about one tenth of the total U.S. mobile source hydrocarbon emissions, and are the largest single contributor to these non-road emissions.

Each weekend, about 54 million Americans mow their lawns, using 800 million gallons of gas per year and producing tons of air pollutants. Since this equipment is used mostly during the hot summer months, when ground level ozone is the highest, it causes problems for asthmatics and aggravates other respiratory conditions.

Westerholm found that the worst case of lawn mower PAH emissions totaled more than 4,000 micrograms per hour using unleaded fuel without a catalytic converter. Average emissions dropped to almost 800 micrograms over the same time period with the addition of a catalytic converter, he said.

Some PAHs, including a few in lawn mower emissions, are classified as probable carcinogens by the U.S. Centers for Disease Control and Prevention.

"Obviously, if catalysts will become mandatory on lawn mower engines, and possibly other small engines as well, a significant reduction of exhaust components will be achieved," said Westerholm.

In 1998, the U.S. Environmental Protection Agency (EPA) issued the so called "Phase I" rules, which mandated a 32 percent reduction in emissions for small "non-road" engines. This affects all engines less than 25 horsepower produced after 1997, including mowers, leaf blowers and chain saws.

According to an EPA study prior to the Clean Air Act of 1990, small engines from lawn and garden equipment make up almost nine percent of some types of air pollution. While current mowers meet the reduced emissions standards, catalytic converters would lower emissions levels further, Westerholm said.

In the Swedish testing, the researchers used regular unleaded fuel in a typical four stroke, four horsepower lawn mower engine and found, after one hour, that the PAH emissions are similar to a modern gasoline powered car driving about 150 kilometers (93 miles). A typical push type lawn mower is run for an average of 25 hours per year, according to the Outdoor Power Equipment Institute.

A higher octane fuel known as alkylate also was tested and resulted in lower emissions. Alkylate is difficult to find in the U.S. and significantly more expensive than regular unleaded fuel in Europe.

Catalytic converters are already available on some European mowers, Westerholm reported. The pollution control devices have been required on U.S. made cars since the late 1970s.

"Using a catalyst would help prevent most emissions from small engines," Westerholm said. "Of course, people could also use an electrical powered lawn mower instead."

In March 2000, the EPA ordered major cuts in emissions from lawnmowers, chainsaws, leaf blowers and other small engine powered equipment. By 2007, when the new standards will be fully in place, the ground level ozone pollution caused by these engines will be cut by 70 percent or 350,000 tons each year.

The new emission reduction standards will affect small hand held engines at or below 19 kilowatts, or 25 horsepower, such as those used in lawn and garden equipment. The 20,000,000 small engines sold in the U.S. each year contribute about one tenth of the total U.S. mobile source hydrocarbon emissions, and are the largest single contributor to these non-road emissions.

Some consumers are junking their old, dirty lawnmowers in favor of less polluting newer models

In December 2000, drawing heavily on rules already in place in the U.S., the European Commission proposed a law governing air pollutants from petrol driven non-road mobile equipment, such as lawnmowers and other garden tools.

The directive will establish the first ever European Union limits on such machinery and it follows agreement of similar limits on non-road diesel engined machinery in 1997.

Westerholm's research is reported in the June 1 issue of the journal of "Environmental Science and Technology," a peer reviewed journal of the American Chemical Society, the world's largest scientific society. His research was funded by the Swedish Environmental Protection Agency.

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