WASHINGTON -- The U.S. Supreme court ruled Wednesday that a Los Angeles air regulatory agency cannot force certain public and private fleets to purchase low-pollution vehicles for their fleets.The Engine Manufacturers Association (EMA) sued the South Coast Air Quality Management District (SCAQMD) over fleet rules that required new commercial vehicles to meet strict emissions standards that preempt federal regulations. The fleet rules banned the purchase of many types of new vehicles such as diesel-fueled trucks and buses that had otherwise met federal emissions standards. SCAQMD argued that they were regulating the types of vehicles local fleet-owners could buy, not regulating the manufacturing of these vehicles, and thus did not overstep their power. Yet in an 8-1 decision the Court ruled that “treating sales restrictions and purchase restrictions differently for preemption purposes would make no sense. The manufacturer’s right to sell federally-approved vehicles is meaningless in the absence of a purchaser’s right to buy them.”The ruling came on the same day the American Lung Association released its annual pollution report. Los Angeles-Riverside-Orange Counties ranked as the metropolitan area with the worst air pollution.