The pollution report card is out, and the results are mixed.

In spite of an overall reduction of particle pollutants, air quality in the United States remains quite poor. More than 147 million Americans, almost half of the population, live in counties where levels of ozone or particle pollutants exceed safe levels, according to the 15th annual national report card released by the American Lung Association Wednesday.

Los Angeles had the worst ozone problem. Other sites such as Houston, Washington-Baltimore, Las Vegas, Phoenix, New York City, Cincinnati, Chicago, and Philadelphia also recorded ozone levels beyond permissible limits set by the U.S. Environmental Protection Agency. The EPA sets the current standard for ozone at 0.075 ppm (75 parts per billion) measured over eight hours.

"Fresno-Madera (CA) recorded higher annual particle levels and became the most polluted in the nation for year-round particle pollution," according to the report. Fresno-Madera was also ranked as the most polluted for short-term particle levels. More than 46.2 million people in the country live in regions where year-round levels of particle pollution exceeds national standard limits. The EPA's standard for annual concentrations of particulate matter measuring 2.5 microns or less stands at 12 micrograms per cubic meter.

The report, which looks at air pollution levels for 2010, 2011, and 2012 was obtained from the EPA's Air Quality System, to which various local and state level air pollution agencies report their data.

“The progress we’ve seen in cleaning our air from our first report to our 15th shows that the tools in the Clean Air Act work,” said Harold Wimmer, National President and CEO of the American Lung Association.

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Earlier in 2011, President Obama's decision not to implement a smog plan meant to reduce ground-level standards between 60 and 70 parts per billion, had been criticized by many environmental groups. “We're deeply disappointed that the administration has chosen to leave in place outdated standards that lag far behind what scientists have unanimously recommended," Fred Krupp, president of the Environmental Defense Fund, had said in his statement.

But in a 6-2 ruling Tuesday, the Supreme Court announced that some 28 Midwestern and Southern states will have to reduce emissions of sulfur dioxide and nitrogen oxide from coal-fired power plants. The Court upheld "a 2011 federal rule governing the amount of air pollution some states can let drift across their borders into their downwind neighbors," the Monitor reported.