It’s no surprise that Wasatch Front air is cleaner in the nearly two months since the coronavirus pandemic put the brakes on most driving.
Now, for the first time, University of Utah researchers have quantified just how much cleaner the air is, according to data released Tuesday, and offered a glimpse at how Salt Lake County residents could tidy up their airshed by steering away from driving or switching to low-emission vehicles.
U. researchers crunched air monitoring data gathered during the second half of March, capturing the first two weeks of the economic slowdown resulting from the pandemic’s arrival in Utah. According to the Utah Department of Transportation, traffic along the Wasatch Front dropped by 40% to 50% as the COVID-19 lockdown took hold.
At a result, levels of nitrogen oxide, a key component of tailpipe emissions, plunged, as did fine particulate pollution, according to the new analysis.
“These measurements, taken together, paint a consistent picture of cleaner air from reduced emissions, especially from reduced traffic,” said Logan Mitchell, a research assistant professor in the U.'s Department of Atmospheric Sciences. “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.”
He conducted the analysis using data from Utah Division of Air Quality monitoring stations that record ambient concentrations of various pollutants, as well as from satellite imagery that shows nitrogen oxide levels and ground-based sensors that record carbon dioxide emissions.
“For environmental scientists, this was a once-in-a-lifetime opportunity to study the air quality impacts of fewer cars on the road,” division Director Bryce Bird said. “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.”
Paradoxically, levels of ozone remained about the same, but Mitchell said that was to be expected. This corrosive three-atom molecule of oxygen forms in the atmosphere through a chemical reaction involving sunlight, nitrogen oxide and volatile organic compounds.
The data Mitchell crunched came from a monitoring station at Hawthorne Elementary School in Salt Lake City and additional measurements of carbon dioxide in Sugar House, at the U., and in the southwest part of the Salt Lake Valley.
• Nitrogen oxide, NOx, levels were lower due to traffic reductions, especially during rush hour peaks. Levels of nitric oxide, NO, were 57% lower than average for March, and 36% lower for nitrogen dioxide, NO2, which forms in the atmosphere.
• Ozone, or O3, which is not visible, was about the same as usual at midday but slightly elevated at night. This would be the expected outcome of less NOx in the air, according to Mitchell. This is because nighttime interactions between NOx and ozone breaks down ozone.
• Fine particulate matter, or PM2.5, was down by 59%, particularly at night. Mitchell was unsure whether that was due to reduced overall particulate matter emissions or reduced formation of particulate matter through atmospheric chemistry.
• Carbon dioxide, CO2, levels were 19% and 33% lower than average at the Sugar House and U. stations, respectively.
• Sulfur dioxide, SO2, remained at typical levels. This was not surprising because the Salt Lake Valley has few SO2 emission sources.
Mitchell emphasized that the findings are preliminary and will be updated as more data arrives.
March typically sees some of the best air quality of the year in Utah, but Mitchell believes the findings offer a gauge of how easily air quality could be improved by less driving and, conversely, how quickly it could degrade from increased driving.
“We are seeing the same thing from ground air quality monitoring sites, the satellite imagery and the carbon dioxide monitoring sites,” Mitchell said. “A global pandemic is a terrible way to get good air quality, but I feel this shows the possibility of how good our air quality could be moving out of the epidemic. Taking 50% of cars off the road is kind of like transitioning 50% of cars to electric.”