Despite this week's U.S. Supreme Court ruling, Southern California air pollution officials say they will still attempt to require most large-vehicle fleets to buy low-polluting trucks and cars — a move that is certain to spark more court battles with industry groups, according to an article in the Los Angeles Times on April 29. On April 28, the U.S. Supreme Court invalidated rules that had allowed the South Coast Air Quality Management District (SCAQMD) to require private trash haulers, bus lines, and other covered fleets to buy low-pollution vehicles. But SCAQMD officials maintain the ruling does not bar them from imposing the same requirement on publicly owned fleets or on private firms that provide city services — a contention hotly disputed by the engine manufacturers that prevailed in the lawsuit decided Wednesday. Manufacturers of diesel engines, along with an oil industry group, sued the SCAQMD because it had barred the owners of the private fleets from buying their products in the greater Los Angeles area, despite advances in clean diesel technology. The U.S. Supreme Court concluded on April 28 that the air quality management district had overstepped its authority under the Clean Air Act. Industry groups now say the decision should clear the way for street sweepers, bus lines and others bound by the rule to buy new diesel engines that emit far less pollution than older models. But South Coast Air Quality Management District officials firmly maintain that the new diesel engines, although improved, are still far from clean compared with alternatives such as engines that burn natural gas, according to the L.A. Times article. "The fact is that diesel remains a much higher source of NOx emissions than natural gas, even with the new technology," said AQMD spokesman Sam Atwood in the article referring to nitrogen oxide gases, one of the main ingredients of smog. Atwood contends that the fleet rules allow companies to make a case for diesel trucks or any other technology if they can show it is as clean as natural gas. The 8-1 decision by the court also noted that local officials could still impose fleet rules by receiving the approval of the California Air Resources Board as well as the U.S. Environmental Protection Agency. Air district officials said they would seek such approvals if necessary to save the rules. Traditional diesel engines are among the worst pollution sources in Southern California, contributing heavily to smog-forming gases and particulate matter, tiny particles that can become lodged in the lungs, causing respiratory problems. Heavy-duty diesel vehicles and stationary diesel engines are responsible for 70 percent of the air pollution cancer risks in Southern California, according to a study by the air quality management officials.