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Forty-seven percent of Americans live in counties with unhealthy rates of ozone or particle pollution, according to the annual American Lung Association's State of the Air report, and nearly three-out-of-four Californians are living in polluted cities. 

The report, which uses the most recent EPA data on ozone and particle pollution, finds that the level of particle pollution (which can cause lung cancer) has gone down overall from 2010-2012, but that ozone pollution has spiked. 

National President and CEO of the American Lung Association Harold Wimmer commented that the report should serve as a warning: 

We are happy to report continued reduction of year-round particle pollution across the nation, thanks to cleaner diesel fleets and cleaner power plants. 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. We must meet these challenges head on to protect the health of millions of Americans living with asthma and chronic obstructive pulmonary disease. 

Even though the report marks an improvement in air quality over previous years, the findings seem objectively dismal. Per the study, 8.9 percent of U.S. citizens live in the most polluted American cities and 22 out of the 25 most ozone-polluted cities had more high ozone days on average than in 2013. In California, the Los Angeles Times reports, 77 percent of state residents live in counties with unhealthy air. 

Not surprisingly, the most polluted areas include the country's densely-populated metropolises. The report ranked the 25 most polluted areas in each of three categories: highest ozone levels, most year-round particle pollution, and most short-term particle pollution. Los Angeles, New York City and Chicago appeared on each list, as did Fresno and Pittsburgh. Los Angeles was the worst city in terms of ozone pollution overall, followed by Visalia, Bakersfield and Fresno, respectively. The top (or lowest) four spots in terms of both year-round and short-term particle pollution were filled by Fresno, Visalia, Bakersfield and LA, respectively. 

The rankings work a little differently for the countries cleanest cities, per the State of the Air website

The cities on the cleanest cities lists for ozone and for short-term levels of particle pollution had no days with unhealthy levels of ozone or particle pollution. These lists are not ranked because all the cities earned the same scores. The cities on the list of the cleanest for year-round particle pollution levels are ranked by their average levels of particles, as calculated by the EPA.

Per these standards, the cleanest cities in terms of year-round particle pollution are Prescott, AZ; Cheyenne, WY; Farmington, NY (tied with Cheyenne); and Casper, WY.  

Currently, the EPA is considering passing stricter smog regulations, which would require lower ozone levels, as part of the smog-standard five-year review. If that doesn't pass, we'll see you in Arizona. 

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