New heavy-duty trucks and buses would be virtually smoke-free by 2007 under national standards for cleaner diesel fuel and engines unveiled May 17 by the Clinton administration. The new pollution limits would dramatically reduce the truck and bus emissions that are major sources of California’s two worst air pollutants – smog and particle soot. The highlight of the proposal by the U.S. Environmental Protection Agency is a 97-percent cutback in the sulfur content of diesel fuel. The new fuel standard has potential to seriously affect supplies, adversely affect U.S. consumers, and harm the U.S. economy, said Red Caveney, president of the American Petroleum Institute. However, diesel engine manufacturers, California trucking companies, and environmentalists praised the standards as reasonable and necessary to protect people from pollutants that threaten their health.