It might be officially nicknamed the Golden State, but sometimes, it’s more like the Yellowish-Brown State: California continues to lead the U.S. in dirty air, with nearly twice as many “smog days” as any other state in the union, a recent report by an environmental group found. According to the study of government air-quality data by the U.S. Public Interest Research Group, smog levels nationwide exceeded federal health standards 4,634 times in the summer of 2001, a 10 percent increase over the previous summer — and this summer is shaping up to be even worse. Texas, Pennsylvania, New Jersey, and Ohio rounded out the worst-five list in 2001. Texas, Michigan, Massachusetts, Maine, and Rhode Island were the only states to show improvements over 2000 air-pollution levels. The U.S. PIRG report comes as the Bush administration is attempting to ease regulations governing emissions from power plants, one of the leading sources of air pollution.