Emissions of two major air pollutants in Salt Lake City have declined dramatically in the last 20 years — but there's still more work to be done.
Haley Humble is a doctoral candidate at University of Utah in the Atmospheric Sciences department. This month, she and her advisor John Lin published a study in Atmospheric Environment.
It detailed a significant decline in carbon monoxide and nitrogen oxides levels in Salt Lake City. Both are major air pollutants.
But the study wasn’t just asking whether those pollutants declined. It was asking why.
“These pollutants are primarily emitted by vehicles," Humble said. "And so we attributed a lot of the larger declines seen over nearly 20 years to these two emission chemical species."
Humble explained that the declines in carbon monoxide and nitrogen oxides are mostly due to more advanced technologies designed to keep those gases out of the atmosphere.
The third gas they studied was a little different: carbon dioxide, or CO2.
“CO2 is basically a proxy for fossil fuel combustion,” Humble said.
CO2 is a major greenhouse gas and a major contributor to human-induced climate change. Human-caused CO2 emissions add more carbon to the atmosphere than natural systems can absorb — and as atmospheric CO2 increases, global temperatures continue to rise.
Those emissions are substantial in Salt Lake City, and did not significantly decline over the last 20 years the same way carbon monoxide and nitrogen oxide did.
However, in Humble's paper, she and Lin found that CO2 emissions have not significantly increased either, even as the city’s population and development grew.
They even temporarily decreased during the COVID-19 pandemic, which Humble said established a "clear and lasting shift."
“We are seeing a decline in emissions, which is wonderful, but we cannot stop here," Humble said. "We have to continue to decline emissions for the betterment of society and the betterment of the next generation.”
She hopes her study can help show that cleaner air is possible, but continued progress depends on science reaching the public.
“The only way that air quality and air quality science are going to contribute and push further technological advancements is by informing the public," she said.
