After 13 years, the U.S. Environmental Protection Agency is poised to remove the Salt Lake metro region from its list of areas that violate its 24-hour pollution standards for fine particulates.

That’s partly because the state has made efforts to reduce its emissions — Utah’s Air Quality Board has passed more than 20 regulations to reduce industry emissions — and partly because Utah has been, well, lucky.

“Luck is a big part of this,” said Thom Carter, executive director of the Utah Clean Air Partnership, or UCAIR. “Remember, our air-quality problem starts as a weather issue. It all has to do with inversion.”

And temperature inversions, which trap dirty air in the Salt Lake Valley, were less severe from 2016 through 2018. The EPA made the proposal to change the region’s designation based on air-quality monitoring from that three-year period, which showed the area did not exceed the standard for the first time since it was established in 2006.

(The Salt Lake region includes all of Salt Lake and Davis counties and parts of Box Elder, Tooele and Weber counties.)

Just two years ago, the EPA classified the Salt Lake region as a “serious” nonattainment area.

“We’ve reduced our emissions significantly over this period of time,” Carter said. “Additionally, we’ve had great weather patterns in the last three years. But if we go a long time between storms in the wintertime, then we will exceed the limit.”

This is not a case of Salt Lake coming into compliance because the standards were lowered. Actually, when the policy was instituted in 2006, it was for PM10 particulates — a standard that has since been changed to the more stringent PM2.5, measuring particulates one-quarter the size of PM10.

The monitoring averages PM2.5 particulates across 24-hour periods, so the levels could still exceed the standard at times and be in compliance. The EPA’s rules allow an area to exceed the limits for approximately 21 days over the course of three years.

PM2.5 refers to particulates that are 2.5 microns or less in width; the largest are about 30 times smaller than the width of a human hair. They reduce visibility and cause the air to appear hazy when levels are elevated.

Short-term health effects include eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath. Long term, the fine particulates can affect lung function and worsen asthma and heart disease.

Carter pointed to the billions and billions of dollars invested by mining companies and oil refineries to install the “best available technologies” to control their emissions as one reason the PM2.5 levels have fallen. He said individual Utahns have helped, too.

“We’ve seen in our own personal data where people are saying they’re car pooling more than they’ve ever carpooled. They’re not idling as much. They’re trip-chaining,” he said. “People are better aware of their own emission space, and they’re finding ways to be part of the solution.”

Not all Utahns, however, according to a Salt Lake Tribune-Hinckley Institute of Politics poll conducted in January. It indicated about a third of those surveyed had changed their commuting habits to improve air quality.

The change in designation is not yet a done deal. The EPA posted its proposal on the Federal Register on Wednesday; a 30-day period for comments runs through July 5. Comments can be submitted to regulations.gov, identified by docket ID No. EPA-R08-OAR-2019-0081.

Even if it is finalized, it’s not necessarily a permanent change. Monitoring will continue, and Salt Lake City could end up back on the noncompliant list.

“Today is a day for everybody to shake hands and say, 'Congratulations, we've achieved something,'” Carter said. “But this is step one. We're nowhere near being done. And anybody who thinks we're done is crazy.

“We have so much to do just to maintain the standard.”