Mowing the lawn and blowing the leaves off the porch may keep your yard tidy, but it’s spoiling my air.

That’s the underlying message in Environmental Protection Agency regulations released Wednesday that aim to reduce hydrocarbon emissions from gasoline-powered lawn mowers, leaf blowers and other hand-held garden equipment, as well as a other types of non-road machinery including golf carts, household generators, boats and personal watercraft.

The new exhaust emission standards take effect in 2011 and 2012, depending on the size of the engine and its use. Included in the new rule are non-road engines below 25 horsepower.

The EPA has been considering the regulation of small engines since at least the early 1990s, citing the potential health hazards of small-engine emissions. The Washington Post cites reports that a single riding lawn mower “emits as much pollution in an hour as 34 cars.” The New York Times, reporting on the issue in 2006 and citing the California Air Resources Board, said a new lawn mower engine at that time contributed 93 times more smog-forming emissions than 2006 cars.

California enacted tighter emission limits last year, over the objections of small-engine manufacturers. The EPA worked with manufacturers and eventually developed a system they agreed with, the Post said Thursday.

The new regulations are expected to eliminate 600,000 tons of hydrocarbon emissions every year, plus 130,000 tons of nitrogen oxide and 1.5 million tons of carbon monoxide — all three being key greenhouse gases and components of ozone, which can lead to increased health problems.

The regulations call for manufacturers to install catalytic converters on small engines, raising the cost of each piece of machinery $20 to $25, the Times reported in 2006.