More than 147 million Americans live in counties featuring unhealthy levels of either ozone or particle pollution -- that according the American Lung Association's 15th annual "State of the Air" report card. The new report looks at pollution data compiled from 2010 to 2012; last year's report covered data from 2009, 2010, and 2011. This year's air pollution report card was a mixed bag of good and bad news. The good news is: particle pollution around the country continues to improve. According to the report: "Thirteen of the 25 cities with the worst year-round particle pollution reached their lowest levels yet, including Los Angeles, Atlanta, Pittsburgh and Bakersfield." Particle pollutants are tiny pieces of solid and liquid pollution suspended in the air, like soot, smoke, ash, cement dust, etc. Particulate exposure is associated with asthma, lung cancer and other types of heart disease and respiratory problems. The bad news is: ozone pollution is getting worse. As the report indicates, 22 of the 25 most ozone-polluted cities, including Los Angeles, New York City, and Chicago, had more smog-filled days between 2011 and 2012, than it did between 2009 and 2010. Smog -- the result of a combination of coal smoke and vehicle emissions reacting with direct sunlight and ground-level ozone -- is powerful respiratory irritant that can also work to trap other types of pollution over a city. "We are happy to report continued reduction of year-round particle pollution across the nation, thanks to cleaner diesel fleets and cleaner power plants," said Harold Wimmer, CEO of the American Lung Association. "However, this improvement represents only a partial victory. We know that warmer temperatures increase risk for ozone pollution, so climate change sets the stage for tougher challenges to protect human health."