More than 141 million people — are routinely exposed to dangerously polluted air, according to the American Lung Association’s “State of the Air 2019” report. That’s over 7 million more people than the previous year’s report indicated. As climate change continues to cause record-breaking heat, ozone pollution — one of the least controlled and most dangerous pollutants — is getting worse.

Harmful to breathe, ozone is created when pollutants such as gases coming out of tailpipes and smokestacks come into contact with sunlight. Higher temperatures increase ozone formation and spark wildfires that spew more dangerous particles into the air — and these are the hottest cities in every state. 

As one of the states with the highest average temperatures, it’s no surprise then that of the 25 most polluted metro areas in the United States, 11 are in California. 24/7 Tempo reviewed the 25 metropolitan areas with the highest levels of ozone pollution, also known as smog, from the American Lung Association’s annual “State of the Air 2019” report.

In addition to ozone pollution, the ALA report also considers particle pollution, which is measured in short-term spikes in a given year and in long-term annual averages.

Because low-income neighborhoods tend to lie next to industrial districts, highways, and power plants, residents of these communities are often exposed to the highest levels of pollution. And these are the poorest counties in every state. 

Individuals inhaling high levels of these particles are at considerably greater risk of adverse health outcomes. People suffering from asthma, chronic obstructive pulmonary disease (COPD), and diabetes, as well as the elderly and the very young are at an even greater risk. Other health risks include difficulty breathing and cardiovascular-related illnesses. And this is just one of at least 28 dangerous things experts have linked to heart disease.

Click Here to read about the 25 Most Polluted Cities in the US.

To identify the 25 most polluted U.S. cities, 24/7 Tempo reviewed the metropolitan statistical areas with the highest levels of ozone pollution, measured in days in a year when the concentration of ozone, or smog, exceeds the EPA standard from the American Lung Association’s “State of the Air 2019” report.

Short-term particle pollution — which is measured in days with excessive particle pollution levels each year and long-term particle pollution, expressed as the annual average concentration of particulate matter — very small air pollution particles that pose significant risk to human health when inhaled — as well as the number of area residents with asthma, including the number of adults and the number of pediatric cases of the disease — came from the ALA.

The incidence of cardiovascular disease and the number of residents who have been diagnosed with chronic obstructive pulmonary disease (COPD) at some point in their lives also came from the ALA.