traffic air quality

Vehicles travel along 400 North in Logan on Thursday afternoon.

Support Local Journalism

After more than 10 years on the EPA’s watchlist, Cache Valley is meeting federal PM2.5 air pollution standards.

While the “attainment” designation won’t be official until a few more steps, including public comment periods, Cache Valley is the first nonattainment area in Utah to clear that bar.

“It doesn’t mean that all our problems are solved and that we don’t have work still to do,” said Jeff Gilbert, transportation planner for the Cache Metropolitan Planning Organization. “But it’s kind of a good sign, I think, something to celebrate, that we’ve met the standard.”

After Cache Valley’s nonattainment designation is lifted, it is expected to enter a “maintenance” regulatory phase. The EPA will still be watching PM2.5 levels in Cache and Franklin counties, Gilbert said, but bad air days won’t mean that local officials have to go all the way back to the drawing board.

“If we do slip back for a time and exceed the standard, there’s kind of some built-in contingency measures that will be put in place or that we’ll be required to implement,” Gilbert said. “Whereas if we weren’t in attainment and we had those violations, it would mean that we’d have to come up with a whole new plan.”

There’s been some talk of the EPA tightening PM2.5 regulations, Gilbert said, so that’s another reason not to get complacent.

“Obviously we still need to remain vigilant and keep doing what we’re doing,” Gilbert said. “But I think it’s a good sign and I think we should have reason to celebrate on some of the steps we’ve taken.”

Vehicle emission levels dipped in 2020 due to coronavirus pandemic precautions. That wasn’t a factor in Cache Valley meeting air quality standards, however, because the deadline for attainment was December 2017 and the data under review for the decision came from 2015-2017, according to the proposal to move the Idaho side of the valley into attainment published by the EPA on Wednesday.

“The good news is that since then we’ve also had, in 2018, 2019 and 2020, we’ve continued to attain the standard,” said Becky Close, air quality policy section manager at the Utah Department of Environmental Quality.

Officials credit a number of efforts for Cache Valley’s improving air. EPA requirements for vehicle exhaust have been getting more strict over the years, so one of the biggest factors in cleaner air locally is that older vehicles are aging off the road.

“It’s really quite remarkable how much cleaner newer cars are than older cars,” Gilbert said. “They say the new 2017 cars with the new Tier 3 fuel are nearly as clean as a CNG (compressed natural gas) car.”

To speed up the process of getting local vehicles more in line with newer pollution-reducing technology, Cache County implemented vehicle emissions tests in 2013, and though the County Council scrapped the tailpipe emissions requirement in 2018, Close and Gilbert credit the program with helping the area reach attainment.

“The reason that we’ve seen that trend is actually because of these state implementation plans, for the most part,” Close said.

Programs to limit woodburning stoves on inversion days and to replace or convert older stoves so they pollute less have helped, as well, according to Close. While people are relying less and less on fireplaces to heat homes in the winter, woodburning stoves can have an outsized effect on air quality because the smoke from partially combusted wood contains PM2.5 particles themselves as well as nitrogen oxides and volatile organic compounds, two of the ingredients in the chemical reactions that create most of the valley’s PM2.5 pollution, Close said.

A program to help organizations reduce emissions from heavy-duty diesel engines has replaced 35 school buses and 15 trucks in Cache County and still has about $1 million left in available funding, according to DEQ spokesperson Ashley Sumner.

“And then we’ve also seen really great behavior changes with the general public,” Close said, “so people knowing when not to burn in their fireplaces, not idling when they’re getting fast food or picking up their kids from school, as well as making sure that they’re grouping their errands together when they’re out in the car.”

PM2.5 pollution refers to particles in the air that are 2.5 micrometers in diameter or smaller. Such small particles pose special health risks because they are small enough to enter lung tissues or even the bloodstream, where they can cause or aggravate cardiopulmonary conditions, according to the EPA.

Cache Valley’s bowl shape makes it prone to winter inversions, when colder air is trapped lower in the valley. The longer an inversion lasts, the more pollution has a chance to build up in the stagnant air. Chemicals from industrial and automobile pollution rise to the top layer of the inversion and, when exposed to sunlight, combine with ammonia emissions from the agriculture industry to form PM2.5 particles.

Because Cache Valley agriculture emits so much ammonia — and because there are fewer practical ways to regulate those emissions — efforts to curb PM2.5 pollution locally have focused on the other precursors, including emissions from vehicles and wood-burning stoves, according to Close.

Ammonia concentrations in Cache Valley air are so high — three to four times higher than at other monitoring sites on the continent, according to USU professor Randy Martin — that much of it already goes without reacting with nitrogen oxides and volatile organic compounds to form ammonium nitrate PM2.5. Limiting the other ingredients, therefore, has the biggest effect on bringing PM2.5 concentrations down.

“We are continually trying to improve our ammonia inventory,” Close said. “The ammonia inventory is something that we haven’t had a really good handle on in the past, and it’s certainly part of the equation and it’s something that we are continually looking at, but it’s pretty complicated so we’re continuing to do research projects and learn from researchers up at USU like Randy Martin, as well.”

Multiple programs are available to help local residents reduce their contributions to air pollution, including:

— The Vehicle Repair and Replacement Assistance Program, which helps people pay for improvements on or replacements of vehicles that fail emissions inspections. To apply, visit

— The Wood Stove and Fireplace Conversion Assistance Program, which helps people pay to convert woodburning stoves to gas. No awards in the Cache County area are currently available, according to Sumner, but that’s expected to change later this year. For more info, visit

— The Clean Diesel Program, which helps fleet owners voluntarily reduce emissions from heavy-duty diesel engines. For more info, visit

Please be aware that Cache Valley Publishing does not endorse, and is not responsible for alleged employment offers in the comments.