Nearly half the country is exposed to unhealthy air that poses serious health risks, according to a new report from the American Lung Association, which warns that climate change is threatening decades of remarkable progress in cleaning up the air.

Air pollution levels keep getting worse for more people in the US, according to a new report, and experts say the Trump administration’s proposed deregulation plans will make it even harder for people to get clean air.

Despite improvements in air quality in past decades, 156 million Americans still breathe in too much soot or ozone, says the annual State of the Air report from the American Lung Association.