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Keep holding your breath. The winter smog's here for the weekend — and likely to choke us again once next week's storms pass.

That seems to be the consensus of forecasters whose predictions had given northern Utahns some hope that Thursday's rain might scrub out the air pollution that's been building for two weeks. That hope crumbled as monitors from the Cache Valley to Tooele, through the Utah and Salt Lake basins, and even Uintah County logged "unhealthy" levels of PM 2.5 particulate pollution.

"I would really be surprised if it completely cleaned out today or tomorrow," Bo Call said Thursday. He oversees air monitoring for the Utah Division of Air Quality.

Call pointed out higher temperatures for the next few days could help ease the pollution buildup. So, too, could the increasing likelihood of precipitation beginning Sunday.

State climatologist Rob Gillies said there's good reason to think another high-pressure ridge will follow soon after the next round of storminess and bring with it the associated pollution-trapping inversion. His team at the Utah Climate Center updated its analysis of weather patterns and found evidence suggesting that there will be another eight to 10 days of high-pollution conditions after Sunday.

"We're going to have another inversion in February," he said.

Several northern Utah counties — Cache, Davis, Salt Lake, Utah and Weber — have already exceeded the U.S. Environmental Protection Agency's health standard of 35 micrograms of pollution per cubic liter of air more than a dozen times thus far this season. Box Elder has exceeded it five times and Tooele 10 times thus far. It's a marked difference from last winter, when the state did not exceed the health-based standard at any site.

Meanwhile, the Utah Division of Air Quality has been puzzling over the remarkably high readings in Utah County. Monitor readings for one hour there hit 147 micrograms of pollution per cubic meter of air — more than four times the EPA's health-based standard of 35.

Plus, daily average levels remained at well above three times acceptable levels, making them the highest levels the state's ever recorded for the area.

Call pointed out that Utah County no longer has the big industrial sources of pollution that people might associate with big emissions, like the defunct Geneva Steel plant. His educated guess: Low temperatures have allowed Utah Lake to ice over, and it's fueling the buildup.

"That lake being frozen is like one big mirror," said Call.

In the Cache Valley, PM 2.5 hourly readings reached 120 on Thursday. Even without industrial sources, it's a pollution trap, a snowy bowl that holds the dirty exhaust from cars and homes and everyday life in a cold pool.

On Tuesday, the Cache County Council signaled that it will stop fighting state and federal regulators and adopt an emissions testing program for vehicles this year.

Certain they had a better solution for their community with a proposed sticker program, they balked when the EPA and state air-quality officials insisted on the sort of emissions program already used on the Wasatch Front to bring winter smog episodes into compliance with federal law by the end of next year.

"We really thought our program would be better than theirs," said County Executive M. Lynn Lemon, noting that a threatened $50,000-a-day fine was a factor. "We're going to move forward."

State air-quality scientists have been working on broader plans to reduce winter smog, but they are searching for even more pollution-cutting ideas because plans for Salt Lake and Utah counties still cannot meet federal standards.

Meanwhile, those emissions cuts won't come in time to deal with this month's pollution, since the improvements are expected to be gradual.

Twitter: @judyfutah