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Smog Lake City: The Science of Inversions and Plan to Clean Utah’s Air

When it comes to pollution problems along the Wasatch Front, many factors are within our control, but some are outside our purview. 


Often, the first thing associated with Utah's air quality concerns: inversions. And rightfully so. Along with record-breaking winter snowfall comes prolonged periods of trapped smog throughout the valley.


Inversions are meteorological events that naturally occur in landscapes like Salt Lake City — valleys situated between mountains, creating a bowl-like effect.1


Typically, the air is warmer near the ground and colder at higher elevations, but during an inversion, it’s flipped. Warmer air settles on top of the valley and traps colder air, and all of the pollution, beneath it.1 Putting the lid on a dirty air-filled Tupperware. 


Inversions are more common during winter months as snow reflects heat instead of absorbing it, clearer and longer nights promote cooler air, and a lower sun gives off more heat to the atmosphere and less to the surface. Additionally, inversions spike during high-pressure systems — prolonged periods of non-active dry weather — and generally form after a storm cycle has moved through the region.1 


Along with the weather-related side of inversions, a chemistry factor is just as significant.


As air quality modeler Marcus Trail tells us on the latest episode of the O₂ & You Podcast, "When things are emitted into the atmosphere, they don't just stay what they are." 


A single chemical in the air may not be dangerous on its own, but a reaction occurs with other compounds and the sun (even if we can’t see the sun, it is still reacting with the air up above us), Trail explained. This process, known as secondary formation, creates water droplets and other particles that can be more harmful than PM2.5, essentially supercharging the inversion.


TLDR: we can’t control when, where, and how inversion occurs.


So, what can we do when it comes to inversions? Control our emissions.


When an inversion settles above our valley, everything we emit from large manufacturing plants, vehicles, and homes and buildings is trapped beneath it.


Without an inversion, pollution disperses throughout the atmosphere. But the inversion’s lid keeps everything trapped and concentrated near the ground, resulting in a high Air Quality Index (AQI) number, affectionately known as a “bad air day.” These conditions also produce the chemical reactions that hypercharge the buildup of gunk in our air.


AQI takes into account PM2.5 pollution (particulate matter of dust and soot that are 2.5 micrometers and smaller) and ozone pollution (formed when chemicals react with the sun).2 Size of the particulate matter is important to note because PM2.5 is small enough to pass through our bodies and directly impact our lungs, according to Trail.  


O₂ Utah’s legislative framework, Prosperity 2030, aims to tackle this exact problem. Prosperity 2030 is a series of bills to reduce our emissions by 50% by 2030 so when the inevitable inversion rolls around, we are trapped in a much cleaner Tupperware.


In 2023, we worked with the Utah Legislature to implement one idea from Prosperity 2030. This bill, HB 220, deals with a single pollutant — bromine — that research found makes our inversions 10-25% worse!


We know the problem and we have the plan to reduce our emissions. For too long, our policymakers have stood by and ignored the root causes of Utah’s poor air quality.


Our elected officials can continue down a path of indifference or address our air and health with policy.


Along with our legislative partners, O₂ Utah has outlined the ideas and policies of Prosperity 2030 for the Legislature. It's time to Choose Clean Air.



Photo: Eliott Coda


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