Special Report

The 30 Most Polluted Places in America

Air quality in the United States has been worsening over the last three years — and it’s killing people. While air quality had been improving since 2009, the trend reversed in 2016. Nearly 10,000 premature deaths have been attributed to this increase alone, according to the National Bureau of Economic Research.

As of 2019, more than 141 million Americans live in places with unhealthy levels of air pollution, according to the American Lung Association’s 2019 State of the Air report. This is significantly more than the 134 million people reported in 2018.

24/7 Tempo reviewed the 30 metropolitan areas with the highest levels of air pollution using data from the Environmental Protection Agency’s Air Quality Index.It takes into account the amount of carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide into the air, as well as the estimated concentration of PM2.5 and PM10. The 24-hour concentration of PM2.5, the most harmful type of air pollution, is considered unhealthy when it rises above 35.4 μg/m3.

PM2.5 — shorthand for particulate matter that is 2.5 micrometers in diameter or smaller. These fine particles are produced by burning fuel – car engines, factories, domestic heating — or by chemical reactions that take place in the atmosphere.

There are three major reasons that air pollution is getting worse in the United States, according to experts: booming economic activity, increases in wildfires, and more relaxed enforcement of clean air regulations.

Another harmful type of pollution is ground-level ozone. It forms when pollutants produced by cars, power plants, industrial boilers, and other sources react with sunlight. The hotter the days, the higher the levels of ozone pollution.

Whether from fine particles or ozone, air pollution can have serious health consequences. They range from effects such as asthma attacks from short-term exposure to pollutants to heart disease and lung cancer from long-term exposure.

Bad air quality isn’t a concern just in the U.S. An estimated 90% of the world’s population breathes dangerously polluted air — these are the 30 most polluted cities on Earth.

Click here to see the 30 most polluted places in America. 


To identify the most polluted places in America, 24/7 Tempo reviewed the EPA’s Air Quality Index (AQI) for Core-Based Statistical Areas (CBSA), otherwise known as Metro / Micropolitan Statistical Areas. The AQI for each CBSA was calculated every day by the EPA using monitored criteria gasses (carbon monoxide, nitrogen dioxide, ozone, and sulfur dioxide) and the estimated concentration of PM2.5 and PM10, which stands for particulate matter smaller than 2.5 and 10 micrometers in diameter. The number of days the AQI was calculated for each CBSA, the percentage of good, moderate, unhealthy, and hazardous days in each CBSA, and days with dangerous levels of criteria gasses all came from the EPA report. Total population data is from the American Community Survey 2017 5-Year Estimates.

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