The 15 Most Polluted Cities in the United States

smog in los angeles one of the most polluted cities in the U.S.

Smog encircles the Los Angeles skyline in 2015. L.A. is one of the most polluted cities in the United States. | Mark Ralston/AFP/Getty Images

Some Americans breathe easier than others. Although overall air quality in the United States has improved in recent years, 4 out of 10 people in the country still live in counties with unhealthy levels of pollution, according to the American Lung Association’s 2017 State of the Air report.

The 18th annual version of the report looked at ozone pollution, short-term particle pollution, and average annual particle pollution in cities across the U.S. While year-round particle pollution and the number of high ozone days is dropping, short-term particle pollution — or daily spikes in air pollution caused by soot — increased in several of the most polluted cities.

Americans are moving away from coal as an energy source, spending less time behind the wheel, and buying more hybrid and electric cars. So what’s causing the increase in short-term air pollution? Climate change, according to the Lung Association. Droughts, wildfires, increased heat, and other changes in climate all contributed to the rise in unhealthy air days in many cities.

“This report adds to the evidence that the ongoing changes in our climate make it harder to protect human health,” said Harold Wimmer, president and CEO of the American Lung Association.

Climate change isn’t the only thing the Lung Association is worried about. The Clean Air Act of 1970 was instrumental in improving air quality across the U.S., the organization noted. Keeping the law in place is essential to refrain from backsliding in terms of air quality. Some are nervous about President Donald Trump’s promised cuts to the EPA, which enforces the Clean Air Act, and what they could mean for air quality in the U.S.

“As we move into an ever warmer climate, cleaning up these pollutants will become ever more challenging, highlighting the critical importance of protecting the Clean Air Act,” Wimmer said.

While polluted air is a concern across the country, these 15 cities are more likely than others to experience the occasional spikes in pollution the Lung Association is especially worried about.

14. Anchorage (tie)

sled dogs

Sled dogs walk on a street in Anchorage. | Jim Watson/AFP/Getty Images

Alaska might be America’s last great wilderness, but the air in the state’s largest city isn’t always pristine. From 2013 to 2015, the Anchorage metro area experienced a weighted average of eight days a year when levels of short-term particle pollution reached unhealthy levels. Many Alaskans rely on wood-burning devices for heat during long, cold winters, the Lung Association said. And that’s one reason for the spikes in pollution.

Note: The Lung Association ranked cities for short-term pollution by looking at the number of days when the Air Quality Index drifted into the unhealthy range. Days when higher levels of pollution were measured were given a greater weight when determining averages.

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