As stay-at-home measures went into place in March 2020, many wondered how fewer cars on the road would impact Salt Lake’s air quality. The first preliminary measurements are now in. Air quality along the Wasatch Front in March is usually good, but the reduction in emissions from COVID-19 stay-at-home measures have made air quality even better than usual.

The results here are some of the first to integrate ground-based air quality and greenhouse gas emissions with satellite observations to understand how emissions have changed .

“These measurements, taken together, paint a consistent picture of cleaner air from reduced emissions, especially from reduced traffic,” said Logan Mitchell, research assistant professor in the Department of Atmospheric Sciences at the University of Utah, who conducted the analysis using data from Utah Department of Environmental Quality (DEQ) monitoring stations. “It shows how fast the air quality improves after a reduction in emissions and suggests that as the economy starts to recover and emissions ramp up, we’re going to see our air quality get worse again.”

“For environmental scientists, this was a once-in-a-lifetime opportunity to study the air quality impacts of fewer cars on the road,” said Bryce Bird, director of the Utah DEQ’s Division of Air Quality. “We are looking forward to further analyzing the data our monitors collected during this period when residents were teleworking and driving less. Dr. Mitchell’s initial analysis shows a lot of promise and hopefully, the final results will help inform behavior and policy in the coming years.”

March air quality by the numbers

Measurements of all air pollutants come from a monitoring station at Hawthorne Elementary in Salt Lake City and additional measurements of carbon dioxide come from monitoring stations in Sugarhouse, at the U, and in the southwest Salt Lake Valley. The measurement period reported here is the last half of March since many of Utah’s stay-at-home measures were in effect by March 15.

• NO_x (oxides of nitrogen) levels were lower due to traffic reductions, especially during rush hour peaks. Nitric oxide (NO) levels were 57% lower than the average March, and nitrogen dioxide (NO₂) was 36% lower than average.
• O₃ (ozone) is about the same as usual at midday but slightly elevated at night.  This is characteristic evidence of less NO_xin the air and less reaction between NO_x and ozone at night. It’s consistent with what scientists think urban air would look like with decreased NO_x  emissions.
• PM_2.5 (particulate matter) is down by 41%, particularly at night. It’s not clear yet whether that’s due to reduced overall particulate matter emissions or reduced formation of particulate matter through atmospheric chemistry.
• CO₂ (carbon dioxide) levels are at 19% and 33% lower than average at the Sugarhouse and U stations, respectively.
• SO₂ (sulfur dioxide) is around typical levels. Mitchell says this isn’t surprising, as there aren’t many SO₂ sources in the Salt Lake valley.

More analyses are forthcoming, and the data have not yet been peer-reviewed, Mitchell says. Also, analyzing the weather conditions from March 2020 will provide a more complete picture of how emissions compare to previous years.

“These results give me a lot of optimism about the future,” Mitchell said. “It shows that as we recover from the pandemic if we invest in clean energy and electric vehicles, it’s really possible to clean up the air.”

Read the full report of preliminary results, including images, here.

Find current air quality conditions from the Utah DEQ here and measurements from stationary and mobile air quality monitors through the University of Utah here.