The EPA is cracking down on pollution from lawnmowers, weed-trimmers, and chainsaws with new rules announced yesterday. It may seem like small potatoes, but 20 million small engine-powered devices are purchased by Americans each year, and together these devices are the second-largest contributor to smog after automobiles. The new EPA pollution rules, to be phased in over the next seven years, will reduce emissions of smog-forming pollutants by 350,000 tons each year and improve the fuel efficiency of small engine-powered equipment by 30 percent. Enviros gave the new rules a thumbs-up.