The Environmental Protection Agency (EPA) reports small, spark-ignited engines at or below 25 hp contribute about 20 percent of hydrocarbon emissions and 23 percent of carbon monoxide emissions from non-road mobile sources. These engines, which usually run on gasoline, power lawnmowers, string trimmers, leaf blowers, chain saws, commercial turf equipment and lawn and garden tractors. The EPA implemented Phase 1 regulations in 1997 that required new small SI engines follow emission standards for hydrocarbons, carbon monoxide and nitrogen oxides. The standards have resulted in a 32-percent reduction in hydrocarbon levels. The newly adopted Phase 2 standards for non-handheld equipment phase-in between 2001 and 2007 and will result in an additional 60-percent reduction in hydrocarbon and nitrogen oxide emissions beyond Phase 1 levels. Phase 2 standards for handheld equipment phase-in between 2002 and 2007 and will result in an additional 70-percent reduction in hydrocarbon and nitrogen oxide emissions beyond Phase 1 levels.

Source: The Environmental Protection Agency (www.epa.gov).