Air quality slipping after years of improving

After decades of improvement, America's air may not be getting any cleaner.

Over the last two years, the nation had more polluted air days than just a few years earlier, federal data shows. While it remains unclear whether this is the beginning of a trend, health experts say it's troubling to see air quality progress stagnate.

There were 15% more days with unhealthy air in America both last year and the year before than there were on average from 2013 through 2016, the four years when America had its fewest number of those days since at least 1980.

President Donald Trump has repeatedly claimed just the opposite, saying earlier this month in Ireland: "We have the cleanest air in the world, in the United States, and it's gotten better since I'm president."

That's not the case. There were noticeably more polluted air days each year in the president's first two years in office than any of the four years before, according to new Environmental Protection Agency data.

The Trump administration is expected today to replace an Obama-era rule designed to limit emissions from electric power plants. Called the Clean Power Plan, it would have gradually phased out coal-burning power plants emitting both air pollutants and heat-trapping gases responsible for climate change.

Air quality is affected by a complex mix of factors, both natural and man-made. Federal regulations limiting the emissions of certain chemicals and soot from factories, cars and trucks have helped dramatically improve air quality over recent decades. In any given year, however, air quality can be affected by natural variations. That may be what's behind the stalled progress, scientists say.

"What you're seeing is a flattening off of progress as opposed to a major change in the wrong direction," said former deputy EPA administrator Bob Perciasepe, president of the Center for Climate and Energy Solutions.

But Trump is moving to loosen regulations on coal-fired power plants and vehicles scientists credit for cleaner air, and he appears to be less stringent about enforcing current rules, according to data obtained by environmental advocates through the Freedom of Information Act.

Scientists said it is too early to see the effects of changes in environmental policy of the Trump administration, which took office in January 2017.

But they added looser restrictions and lax enforcement would almost certainly reverse the gains made in recent decades, potentially turning what has so far been a modest, two-year backslide into a dangerous trend.

"Today it feels like the future of our kids and our country is at stake," said former EPA chief Gina McCarthy. "We do not have the cleanest air, and we have not crossed the finish line when it comes to pollution."

The EPA quietly posted new air quality data online last month showing a recent uptick in polluted days.