Editor’s note: This is the second in a series of articles on air quality in Tooele County.
Air pollution in Tooele County is a complex issue. For example, one year before the county saw the worst inversion episodes on record, area residents actually drove less.
That’s not to say cars aren’t an important part of the air pollution equation. Bryce Bird, director of the Utah Division of Air Quality, said cars are by far the single largest contributor to pollution in Salt Lake and Tooele valleys.
“Each car doesn’t emit a lot,” he said. “But just the fact that there are so many cars, leads them to being the leading source.”
Though Tooele County is far less populous and polluted than Salt Lake County, it too has its own share of cars. According to statistics from the Utah Department of Transportation, local residents drove a combined average of 2.25 million miles per day in 2012.
All those miles, however, represent a decrease from 2011, when residents drove an average 2.31 million miles per day, and is lower still than 2007, when the number of miles commuted in the county peaked at 2.5 million miles — nearly 1 billion miles for the entire year.
However, Tooele County’s 2012 average is still twice what the daily mileage was in 1988. UDOT’s earliest available records show that just 25 years ago, residents collectively averaged just over 1 million miles per day.
All those miles add up quickly. Even then, cars don’t emit a large quantity of PM 2.5 particles themselves, Bird said — those typically come from solid fuels, such as wood and coal. So where does Tooele County’s particulate pollution come from?
Understanding the answer requires a little scientific explanation, said Bird. There are actually two kinds of PM 2.5 particles. One kind is emitted directly into the atmosphere by various sources. The other is actually created via a chemical reaction in the atmosphere itself. The latter are far more common in Utah, Bird said.
These atmospheric particulates form when certain chemicals condense into particles under a specific set of conditions that Utah’s valleys are prone to develop. A number of gasses can contribute to the creation of PM 2.5, including ammonium nitrate and a grouping of chemicals known as volatile organic compounds, both of which are abundant above Utah’s cities.
An inversion situation can exacerbate poor air quality in Utah because it contributes to the formation of PM 2.5. When a layer of warm air traps cool air beneath it, gasses released into the atmosphere have no outlet. This increases the concentration of precursor chemicals beneath the inversion layer.
Additionally, Bird said, the cold air trapped under the inversion will prevent snow from melting. Unmelted snow reflects light back into the smog, which accelerates the formation of PM 2.5.
The presence of snow during the extended inversions of 2013 were important factors in the poor air quality that developed that year, said Bird.
Though cars are a significant contributor to air pollution, they are far from the only culprits. Bird identified multiple household sources of chemicals that contribute to PM 2.5 formation — including hair spray, cleaning and cooling agents, detergents, and even fertilizer.
One of the new rules created under the state’s implementation plan will help reign in household contributors, Bird said, by increasing regulations on what products sold in Utah can and cannot contain. The products should work the same for the consumer, he added, but should emit some 40 percent fewer pollutants.
Additionally, technological advances continue to help curb local pollution, Bird said. Today’s cars produce far less pollution than older models, even those made in the 1990s. He is confident these and other improvements will allow Tooele and Salt Lake counties to meet their air quality goal by 2019, and believes the state will be able to improve beyond it in time.