Even with tougher pollution standards in place, it could be many years before all Utahns are guaranteed clean, healthy air.

Scientists working for the state Division of Air Quality say they haven’t yet been able to develop an effective pollution-control plan that would keep the tiny airborne particles linked with the Salt Lake Valley’s inversions below limits set by the Environmental Protection Agency.

Barring an unforeseen breakthrough, one scientist said, it is likely Utah will miss a critical 2019 federal deadline for meeting those air-quality standards. And if that happens, it would face legal penalties that could have an economic impact on the Beehive State.

Whatever the consequences, the state Department of Environmental Quality’s current computer models for Utah’s air quality are projecting continued pollution woes for the Salt Lake Valley through at least 2024.

Small particulate pollution, called PM 2.5 for short, is capable of traveling deep into human lungs and is associated with respiratory issues, heart attacks and a plethora of other medical concerns. And the Wasatch Front’s unique geography make it vulnerable to inversions, where a lid of high-altitude warm air traps cold air beneath it, causing pollution to accumulate.

Because the region has violated the EPA’s limits for small particulates for more than a decade, Utah regulators were supposed to submit a new plan for managing the pollutant to the EPA in December.

But they have not turned in the plan yet, according to a newly released year-end report by DEQ — because the state’s own scientists don’t think it’s going to work.

“We’re still not looking like we’re going to meet the requirements that were needed by the Dec. 2019 deadline,” said Chris Pennell, the state’s lead air quality modeler.

Computer models through 2024 suggest that while most parts of the Wasatch Front respond well to the state’s planned emission controls, those same strategies don’t work as well in the heavily populated Salt Lake Valley. In fact, Pennell said, scientists have yet to find a scenario that lowers small particulate pollution in northern Salt Lake County in line with the EPA’s standards.

“It’s not working out,” Pennell said. “It does appear that we are seeing less modeled air pollution in 2024 … but it still doesn’t give us numbers that help us reach attainment.”

State air quality data appears to confirm what Pennell’s computer models are showing.

Based on data for 2017 — which state scientists are still finalizing — most of the state is on target to meet federal rules, said Bo Call, who oversees air quality monitoring for the state. But, according to Call, Ogden and Salt Lake City remained just above EPA limits of no more than 35 micrograms of particulate matter per cubic meter of air

Salt Lake City was stuck at 36.3, based on the preliminary 2017 data. And that puts Utah’s air quality status very much at the mercy of Mother Nature, Call said.

“Whether we’re close or not close, all depends on the weather,” he said. “If we get into an inversion that’s going to last a couple of weeks, we’re going to go over the standard.”

State scientists have even modeled scenarios that eliminated all emissions from industry from the Salt Lake Valley, Call said, and found that 8-9 days into an inversion, the valley still ends up violating the EPA standards due to emissions from vehicles.

Jessica Reimer, a policy associate with the nonprofit group HEAL Utah who has participated in the state’s air quality planning, called the state’s findings “very concerning.”

“This is more evidence that we need to take any and all measures to reduce our emissions in the valley,” Reimer said. “Especially as we continue to have our population grow. It’s only going to get worse.”

With less-polluting vehicles coming on the market and area refineries pledging to produce cleaner fuel for Utah drivers, the state stands to see significant reductions in emissions from its largest source of air pollution — automobiles.

But as Utah’s population continues to grow and the number of vehicles increases, Pennell said, computer models indicate that emissions from those new sources eventually will erase other gains over time.

“As cars get cleaner, that will go down,” Call said, “but at some point you get enough new cars from new people that the decline from cars getting cleaner is going to level out and go back up.”

If Utah can’t develop a pollution-control plan that works by 2019, the EPA could force it to adopt what are called the “most stringent measures,” meaning state regulators would have to deploy regulations or technologies in use elsewhere in the U.S. to control PM 2.5, without regard for cost or economic impact.

In a statement, an EPA spokeswoman said it was still too early to discuss the ramifications of missing the 2019 deadline. The EPA continues to work with Utah to produce a plan to control particulate pollution in a timely manner, according its statement.

In a recent interview, regional EPA administrator Doug Benevento expressed optimism about Utah’s prospects for reaching the EPA standard.

But the prospect of tougher controls is why Utah’s refineries have willingly agreed to move toward technologies such as making cleaner Tier 3 vehicle fuels, Reimer said — they want to avoid more stringent measures, which will likely involve significant costs.

“Down the line,” she said, “they may not have a choice.”

And while HEAL Utah advocates for better air quality, the EPA’s recourse of imposing its “most stringent measures” on the state gives even Reimer pause.

“You want people to be taking the measures that will benefit our air quality,” she said, “But I can’t say if most stringent measures would be a good thing, and would hesitate to say that, because it would impact a lot of businesses and could impact our economy.”