Emissions of nitrogen oxides and carbon monoxide have steadily decreased on Salt Lake City roads over the last two decades, according to new atmospheric sciences research conducted by University of Utah scientists in partnership with the National Oceanic and Atmospheric Administration.
Declining Pollutant Trends
The study, which analyzed pollution data recorded continuously between 2005 and 2023, found that while two major pollutants have dropped, carbon dioxide emissions—a gas linked to climate change—have remained steady. This stability in carbon dioxide suggests that total fuel use has not fallen significantly, even as the pollution produced per unit of fuel has improved.
Vehicle Technology Improvements
Researchers attributed the drop in nitrogen oxides (NOx) and carbon monoxide (CO) to advancements in vehicle technology. John Lin, a professor of atmospheric sciences and scientific director of the Wilkes Center for Climate Science & Policy, said that the proliferation of catalytic converters and cleaner new cars have helped curb unhealthy gases from tailpipes.
Shifting Emission Sources
The research also identified a shift in the primary sources of local pollution. While vehicle emissions once dominated the city's air profile, lead author Haley Humble, a graduate student in Lin's lab, noted that other sources such as industry, residential heating, and off-road equipment are becoming relatively more prevalent.
Impact of Pandemic Shifts
The study observed that the COVID-19 pandemic created a lasting change in traffic patterns, with reduced vehicle levels persisting on city streets even after lockdowns ended. Humble noted that increased flexibility through working from home has contributed to this shift.
Monitoring Methodologies
To track these changes, the research team analyzed data from three specific locations: Hawthorne Elementary School on 700 East, the Browning building on the University of Utah campus, and the Rose Park neighborhood near the Salt Lake City International Airport. The researchers utilized a ratio approach to identify specific sources, such as comparing diesel versus gasoline engine signatures.
Ongoing Air Monitoring
The findings, which were posted online in February 2026 and are set to appear in the journal Atmospheric Environment, also noted that the rate of pollution improvement in Utah has slowed over time. Meanwhile, the Utah Department of Environmental Quality's Division of Air Quality maintains a nightly updated air emissions inventory that tracks annual tons of ammonia, particulate matter, carbon monoxide, sulfur dioxide, and volatile organic compounds across the state.
