Utah’s inversion season officially started Nov. 1, and, almost on cue, Salt Lake County’s first inversion of 2019-2020 began building that afternoon.

Over the weekend, state regulators advised Wasatch Front resident to take voluntary actions to reduce the emissions that contribute to the thickening fine particulate matter, or PM2.5, visibly piling up in the haze seen Monday over the Salt Lake Valley.

That means minimize driving, take transit or walk, turn down thermostats and don’t burn solid fuels.

(Trent Nelson | The Salt Lake Tribune) Birds fly over a hazy Salt Lake Valley on Monday, Nov. 4, 2019.

For Salt Lake County residents, that call triggered a mandatory burn ban that is expected to remain in effect for the next several days while stagnant weather persists. Warm air above the valley is holding down cooler air near the ground, trapping emissions from tailpipes, smokestacks, farms and landfills.

"Outside Salt Lake County, we ask that you not burn wood because it contributes to poor air quality, especially particulate pollution, those small particles that get lodged in lung tissue," said Donna Spangler, spokeswoman for the Utah Department of Environmental Quality. "It's being proactive because we are already in an inversion. Even if the air quality isn't near the health standard, we know based on forecasting we are not going to get weather conditions that would remove the pollution. Every day we are in an inversion we are going to continue to build."

The air quality in Utah’s monitored counties Monday was listed as unhealthy for sensitive groups, with the worst readings in Salt Lake County, which recorded a level of nearly 30 micrograms per cubic meter. That’s well below the federal threshold, but Salt Lake County health ordinances still require residents to take mandatory actions, such as refraining from operating wood-burning appliances.

Violations of the burn ban are subject to a $150 fine, which increases for repeat offenders.

“Anytime we drive, we turn up our heat, that is just going to contribute to our air quality problem,” Spangler said. “If you have to drive, try to consolidate trips, avoid idling and drive-thrus.”

Monday and Tuesday are the days residents may apply for up to $4,000 in grant money to convert a wood-burning appliance to one that burns natural gas or propane or runs on electricity. The next registration period is Dec. 3-4. Studies show that wood smoke accounts for up to 15% of the pollution trapped in some of the state’s worst inversions.

While the state’s conversion program is aimed at those who rely on wood for heat, it is open to all residents who operate wood stoves in their homes.

This and other state programs that subsidize the replacement of older, dirtier equipment were put in place to address the Wasatch Front’s long-standing battle against air pollution. Lawmakers have made millions available to encourage people to replace gasoline lawn mowers and snowblowers with electric models, retrofit or replace diesel engines, ride transit, and drive low-emission or electric cars.

During wintry days, northern Utah’s air quality is sometimes among the worst in the nation, but environmental regulators say the state has seen great improvements in the past two decades despite a steady growth in population and in vehicle miles driven.

Improvements have reached a point at which the federal Environmental Protection Agency has proposed to move Salt Lake County to the next phase for controlling and monitoring particulate pollution.

Many activists and officials, including both of Salt Lake City’s mayoral candidates, contend Utah still has a long way to go to boost its air quality and reduce emissions.