"Each weekend, about 54 million Americans mow their lawns, using 800 million gallons of gas per year and producing tons of air pollutants. Garden equipment engines, which have had unregulated emissions until the late 1990's, emit high levels of carbon monoxide, volatile organic compounds and nitrogen oxides, producing up to 5% of the nation's air pollution and a good deal more in metropolitan areas.
According to the EPA, a new gas powered lawn mower produces as much volatile organic compounds and nitrogen oxide air pollution in one hour of operation as 11 new cars each being driven for one hour."
http://www.peoplepoweredmachines.com/faq-environment.htm#environment
Offer a bounty on older gas-powered lawn mowers and reduce emissions by scrapping higher-polluting mowers.