Air pollution plagues millions of Americans, with some regions hit harder than others.

Nearly 64 million Americans are living in areas with daily spikes in particulate pollution, according to a new report from the American Lung Association. The report found that around 63.7 million Americans lived in 111 counties across 19 states with failing grades for unhealthy spikes in particulate matter air pollution during 2019-2021. Particle pollution in the air comes from sources like factory fumes and vehicle emissions and is noted in the report as a “deadly and growing threat” to public health. The report cites the success of the Clean Air Act over the last few decades as a driving factor behind the positive trend.