When a gasoline-powered mower rumbles along a lawn, the tiny puff of carbon monoxide it coughs up is barely noticeable.

But multiply that puff by 44 million — the number of gasoline-powered push mowers

Miriam Mills took advantage of a program that gives Columbia, S.C., residents credit toward an electric lawn mower when they turn in their old gas mower. She now uses a Neuton battery powered lawn mower to cut her backyard.

the U.S. Environmental Protection Agency estimates are in use in the USA — and it's an air quality issue, especially in areas facing the likelihood of violating clean air standards that will take effect Aug. 31, EPA spokesman Dave Ryan says.

More than 300 counties are in violation of federal air quality standards now, and that number is likely to double when new standards go into effect, Ryan says. Plus, additional EPA standards specifically for mowers will go into effect next year that call for a 35% reduction in emissions, he says.

To help improve air quality, communities across the USA are offering residents vouchers and discounts toward purchase of electric or non-motorized mowers when they turn in their gas-powered mowers, says Bill Becker, executive director of the National Association of Clean Air Agencies, which represents air pollution agencies in most states.

"These have not been your traditional methods of reducing air pollution, but they have been very successful when implemented," he says. "We are seeing more examples of these types of programs, ranging from lawn mowers to wood stoves to other high-polluting consumer-owned activities."

Riding mowers are accepted as well as push-mowers, but few have been offered for exchange, he says.

Operating a typical 3.5-horsepower, gas-powered lawn mower for one hour that's not equipped with a pollution-control catalyst creates as much pollution as driving a newer sedan from Washington, D.C., to Boston, Becker says. Newer model mowers have catalytic converters that help turn pollutants such as carbon monoxide and nitrogen oxides into "normal atmospheric gases" such as nitrogen, carbon dioxide and water, according to the EPA's Ryan.

Mower exchange programs going on this spring include:

•Denver: In a city where testing shows lawn equipment contributes up to 10% of the emissions in the area, there will be at least 500 environmentally friendly mowers available on May 1 in an exchange program, says Sarah Anderson of the Regional Air Quality Council. People who exchange a gas-powered mower will get a discount toward the purchase of a battery powered or non-motorized mower, which will be immediately available at the site.

•Boise: On May 1, the city will offer 150 electric mowers at a $110 discount for people who trade in their gas mowers. Also, a drawing will be held, and 50 people will get an additional $125 discount, and one mower will be given away, says Aimee Hughes, environmental specialist for the city's public works department.

•Sacramento: Residents last month sent nearly 1,300 gas-powered lawn mowers for recycling and received discounts on the purchase of electric or non-motorized push mowers, says Carol Novak of the Sacramento Municipal Utility District. The discounts reflected a savings of more than over $220 off the regular retail price, she says.

That agency has teamed up with the Sacramento Metropolitan Air Quality District on this program since 1997. On-site exchange events also are being held in South Carolina, Texas, Vermont and Washington, according to Allison Cranmer, sales manager for Neuton, a battery-powered mower manufacturer offering discounts ranging from $10 to $200 on its electric and non-motorized reel mowers.

The company also is offering "virtual" exchanges, in which participants recycle their gas mower locally, then call to order an electric mower at a discount for delivery, she says. That's available in California, Florida, Idaho, Illinois, Iowa, Maryland, Massachusetts, Missouri, New Jersey, North Carolina, Ohio, South Carolina, Texas and Washington, she says.

Some programs don't even require gas mower trade-ins, she says. First-time mower buyers can, in some cases, also receive discounts to buy battery-powered mowers through programs sponsored by local governments or environmental agencies, Cranmer says.

Mowers that are turned in are usually sent to the local recycling center or solid waste collector and destroyed, Cranmer says.

"One of the big incentives from the residents' point of view is that there's low maintenance involved," says Channell Webster, program coordinator for the South Carolina Department of Health and Environmental Control. "It doesn't require oil, it doesn't require gas. There's also less noise pollution."

Miriam Mills of West Columbia, S.C., is a testimonial to the popularity of the program.

She and her neighbor, Thelma Weathersby, showed up at the trade-in site in Columbia at 4 a.m. on April 10 to make sure they were first in line when the electric mowers came off the truck five hours later.

Mills has a small lawn but says she is "for keeping the environment clean" and will share the mower with Weathersby.

"I just think it's fantastic that they do this program and I hope that they keep it up," she says.

Barnett reports for The Greenville (S.C.) News