The air quality in many cities has improved markedly thanks to improved technology in fuel-burning mechanisms, although problem areas remain, the American Lung Association announced Wednesday. The biggest improvement came as counties studied across the United States lowered the levels of particle pollution in the air. Although weather patterns change air quality, 16 US cities hit their lowest levels of particle pollution ever for the entire year. This included Los Angeles, although it remains the nation's most polluted city for ozone pollution, while Bakersfield topped the list for particle pollution. Many cities benefited from both new practices at power plants fueled by coal and better emissions and engine technology in cars and larger vehicles. Improvement came across the United States, and many areas are seeing the effects of the 1970 federal Clean Air Act. Although some still have dirty air, many of the nation's most polluted cities were slightly cleaner than last year. In Ohio, for example, particle pollution readings improved in Cleveland, making it among 16 cities that reported their lowest levels of particle pollution on record. The American Lung Association lauded the federal Clean Air Act, currently on hold by the Supreme Court, but urged states to individually evaluate their air quality to determine paths to improvement. As scientific information has become more available, cities have been able to make specific plans because they know their targets for clean air.