It also has proposed cutting sulfur content in gasoline by 90 percent. But state regulators and environmentalists said trucks, although far fewer in number, are an equally bad source of air pollution. They want the EPA to require low-sulfur diesel fuel, impose even stricter emission standards than contemplated for 2004 and require inspections to ensure standards are met by trucks actually on the road. The Justice Department disclosed in October that 1.1 million trucks that had passed factory emission inspections actually were polluting much more than allowed because of devices that had been installed illegally to overcome emissions controls. Large trucks account for 3 million tons of smog-causing nitrogen oxide annually and half of the soot that comes from mobile sources.
Diesel fuel contains almost twice as much sulfur as even today's gasoline.
A single heavy-duty diesel truck can emit as much pollution as 150 cars, said Frank O'Donnell, executive director of Clean Air Trust, another environmental group. In many urban areas big trucks are the single biggest source of microscopic soot, and a major contributor to smog. Still, regulation of large trucks is now at about the same stage as regulation of cars in the mid-1970s, said Rich Kassel of the Natural Resources Defense Council. The petroleum industry has pledged to fight an EPA proposal to cut sulfur in gasoline to 30 parts per million from 300 and expressed misgivings about sulfur reductions in diesel fuel. Trucking companies and independent drivers have complained about the added cost of low-sulfur fuel as well as new costs from tighter emission controls.