Air pollution is getting worse.

Nearly 134 million Americans, (41%) live in counties that got at least one "F" for unhealthy air, and have unhealthful levels of either ozone or particle pollution, according to the American Lung Association.

With record-setting heat in 2016, many cities across the U.S. experienced more days when ground-level ozone, (smog) reached unhealthy levels, the ALA reports in its annual State of the Air 2018 report.

Most at risk to the dangers of air pollution are children and adults over 65, and people with asthma or other chronic lung disease, cardiovascular disease or diabetes. Ozone and particle pollution are also both linked to increased risk of lower birth weight in newborns, the report says.

Despite the increase in ozone, the report indicates that actions taken under the Clean Air Act continue to clean up pollution in much of the nation since it was enacted in 1970. The best progress came in the continued reduction of year-round particle pollution, due to cleaner power plants and increased use of cleaner vehicles and engines. Continued progress to cleaner air remains crucial to reduce the risk of premature death, asthma attacks and lung cancer, the report states, and as climate change continues, cleaning up these pollutants will become more challenging.

According to the American Lung Association, these are the cities with the worst air pollution.

Photo: TierneyMJ Shutterstock

This article was written by a staff member of TheStreet.