Emissions of two major pollutants have steadily decreased on Salt Lake City roads over the past two decades, while levels of carbon dioxide emissions, a related gas blamed for climate change, remained steady, according to a new study by University of Utah atmospheric scientists conducted in partnership with the federal National Oceanic and Atmospheric Administration.
The team led by John Lin, scientific director of the Wilkes Center for Climate Science & Policy and a faculty member in the Department of Atmospheric Sciences, analyzed pollution data recorded continuously at three locations in Utah’s biggest city and documented trends that could help Utah tackle its air quality problems.
The study tracked emissions between 2005 and 2023, focusing on three gases linked to human activity: nitrogen oxides (NOx), carbon monoxide (CO) and carbon dioxide (CO₂). These gases are co-emitted when fossil fuels are burned, especially in cars, trucks, homes and industrial processes.
The findings offer proof that emission standards and vehicle improvements have helped curb the amount of unhealthy gases spewing from tailpipes.
“Catalytic converters have proliferated, and the new cars are so much cleaner than what we had before,” Lin said.
The study also shows that pollution sources are becoming more mixed. While vehicle emissions used to dominate, other sources, such as industry, residential heating and off-road equipment, are becoming relatively more prevalent, according to lead author Haley Humble, a graduate student in Lin’s lab.
The findings, appearing in the journal Atmospheric Environment, documented the following:
- NOx and CO emissions have dropped significantly over time.
- CO₂, however, has not decreased much overall, suggesting that total fuel use hasn’t fallen significantly, even as pollution per unit of fuel has improved.
- Over time, the rate of improvement has slowed, meaning Utah is still reducing pollution, but not as quickly as before.
- The COVID-19 pandemic established a clear, lasting shift, with reduced traffic levels persisting on city streets even after lockdowns ended.
“There’s been so much more flexibility since the pandemic, with the ability to work from home or when you can come into the office,” Humble said.
The rapidly growing Salt Lake Valley is home to one of the world’s longest running urban CO₂ observation networks, established in 2001, resulting in a valuable one-of-a-kind dataset, according to Lin.