For years, air quality in the U.S. steadily improved. And just like that, deaths related to air pollution fell off too.

However, in 2017 and 2018, new data show, the amount of fine-particle air pollution got worse, with concentrations rising 5.5 percent after falling by 24.2 percent the previous five years.

The reversal made a real difference in the lives of thousands of Americans. Using reliable formulas that reflect the relationship between pollution and mortality, researchers say in 2018 alone worsening air quality can be linked to more than 10,000 additional deaths.

Fine-particle air pollution — from tailpipes of cars and trucks, and smokestacks at factories and power plants — is very harmful. Measuring less than 1/30th the width of a human hair, it can be inhaled and absorbed into the bloodstream. It has been linked to heart disease and stroke, respiratory disease and lung cancer, as well as dementia and Alzheimer’s disease. It can lead to lower test scores and work productivity.

Regulations have gone a long way in limiting the bad effects of air pollution. But even as pollution fell, by one measurement dropping the number of deaths related to it by 47 percent in the two decades prior to 2010, it could still be blamed in part for 71,000 deaths that year — as many as fatal shootings and car accidents combined. In 2015, even as every county in the U.S. met federal air quality standards, pollution was responsible for more than 30,000 deaths.

It’s a problem, and now it’s getting worse, again.

Americans drove more and used more natural gas the last two years, part of the reason pollution is on the rise. Wildfires, mainly in California, also played a role.

But also cited as a factor were actions by the Environmental Protection Agency, beginning during the Obama administration and given the throttle under President Donald Trump.

Enforcement of the Clean Air Act began to fall off under Obama but fell precipitously under Trump. The Trump administration also has rolled back 24 rules and regulations related to air quality, according to an analysis by The New York Times. Last year, the EPA disbanded a panel of experts that advised the agency on fine-particle pollution, replacing it with consultants from the fossil fuel, pharmaceutical and tobacco industries.

And when the EPA found that eliminating the Clean Power Plan — which sought to lower carbon emissions from power generators — would cost an additional 1,400 premature deaths, the Trump administration decided to change the way such calculations are made.

In short, against all scientific evidence, the EPA now says that cleaner air does not lead to better health.

That is simply not the case. Ignoring the very real problems caused by air pollution will only allow it to get worse, affecting the health of tens of thousands of Americans each year.