This is an archived article that was published on sltrib.com in 2015, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.
While little can be done about the weather conditions that cause Utah's wintertime inversions, air quality leaders say residents can take steps to prevent pollution from building.
The Utah Division of Air Quality (DAQ) predicts that Salt Lake County will experience its first mandatory no-burn day of the year on Tuesday. That doesn't mean Tuesday's air quality will exceed federal standards — rather, the DAQ is hoping to avoid an overage later in the week, said Bo Call, who oversees the DAQ's air monitoring.
Though Utahns sometimes regard inversions as distinct weather events, they're actually more like the winter status quo in northern Utah, Call said.
"As soon as air stabilizes after a front comes through, that's when they set in," he said.
Once calm winter weather sets in, the inversion acts as a lid that keeps all the pollution put into the air in the valley, where it gradually concentrates until the next weather disturbance moves in to clean it all out, Call said.
Ideally, he said, Utah would get some kind of winter storm every three or four days to keep the air clear. When that doesn't happen, pollution builds until it exceeds federal standards.
The forecast doesn't call for another storm in the Salt Lake Valley until Dec. 13.
That's where the mandatory no-burn days come into play, Call said. The idea is that if Utahns can decrease the rate at which they emit pollutants, northern Utah will be able to endure more inversion-capped days between winter storms before air pollution becomes so concentrated that it violates the health standards set by the Environmental Protection Agency.
The trouble is, Call said, that basically everyone pollutes, and not everything is so easy to regulate as wood burning — which is why the DAQ also encourages people to be mindful of their emissions and drive less, or take public transportation on "mandatory action" days in addition to abiding by the wood-burning ban.
"Every day, we all pollute," he said. "Everybody — every car, every business, every home — contributes to pollution."
Salt Lake County had 23 no-burn days last inversion season, with the first period of mandatory action beginning Nov. 20 and the last ending Jan. 27. Salt Lake County tied with Davis County for the largest number of mandatory action days last year.
During those mandatory action periods, the DAQ cited 12 Utahns for violating the wood-burning ban — five citations went to residents in Weber County, five to residents in Utah County and two in Salt Lake County, according to Jay Morris, the DAQ's manager of minor-source compliance.
But there is some good news in the mix, Call said. In recent years, the average number of inversion days Utah can absorb before violating federal standards has increased from three days to four days.
It's just not clear why that is, he said.
"There isn't one smoking gun; there are lots of reasons that may have happened," Call said.
In addition to the increased enforcement and advertisement of mandatory action days, Call said, Utah has seen a growing number of homes retrofitted to be more energy efficient, and newer cars and fuels on the market are cleaner than past technologies. Climate also plays a role, he said. Pollution tends to build faster when winter weather is colder than normal, especially if there is snow left on the ground.
And the inversions themselves, while relatively constant in their presence, are variable in their intensity. If the inversion layer occurs higher in the atmosphere, it takes longer for pollution to build up in the valley.
The current trend is positive, Call said, especially as reduced-emission Tier 3 fuels come on the market and as Utahns continue retiring old vehicles in favor of new models, which are substantially cleaner, or even electric cars.
But Call said he's still hoping to get some help from the weather — meaning either frequently stormy weather or warm temperatures and little snow, like last year.
"If we get into a situation where we're not being favored by routine storms, then that's the time of year when we tend to have long inversions," he said. "And it's hard to keep our numbers low when we have an inversion that's four days or longer."
Twitter: @EmaPen