The Salt Lake Valley’s summertime ozone pollution is a complicated puzzle because so many different kinds of emissions contribute to the problem, which in turn is affected by the time of day or year, the weather and many other factors.

Without knowing which emissions are most culpable or understanding the role of the region’s topography, solutions to Utah’s ozone mess will remain elusive.

In collaboration with University of Utah faculty and funding from the state, the National Oceanic and Atmospheric Administration (NOAA) is helping find answers.

A team of NOAA scientists is in Salt Lake City for the next few weeks gathering masses of air quality data that is expected to yield new insights that could help bring relief. Building on a long record of air quality data compiled by U scientists and the Utah Division of Air Quality (DAQ) over several years, this new snapshot data is hoped to illuminate what is driving elevated ozone levels along the Wasatch Front, according to Steven Brown, one of the NOAA research chemists leading the Utah Summer Ozone Study.

“Every city in the United States has an ozone problem, but every city is also different in terms of the sources that contribute to that ozone. And Salt Lake is no exception in that regard,” Brown said. “We’re certainly trying to understand the influence of wildfires. But then you’ve got this mix of industrial and urban sources in a valley with very unusual meteorology. We’re trying to characterize all those sources. What does that meteorology look like, and how do those things combine to produce the unique ozone problem that affects Salt Lake City?”

NOAA’s multi-platform study is being coordinated with the U’s Utah Atmospheric Trace Gas & Air Quality (UATAQ)) lab, headed by John Lin, a professor of atmospheric sciences. Also involved is Lin’s colleague Gannet Hallar, whose students are launching weather balloons and providing weather forecast briefings most days of the study to support NOAA’s regular overflights.

While Utah has made strides in reducing the severity of its particulate pollution-trapping winter inversions, summertime ozone has worsened to the point that Salt Lake City is out of attainment of the federal standard.

The valley often experiences summer afternoons where concentrations spike above the ozone standard, set at 70 parts per billion. Exposure to this gas can damage lung tissue and harm sensitive ecosystems. A highly reactive, unstable three-atom oxygen molecule, ozone is not directly emitted into the atmosphere. Rather it typically forms when two categories of pollutants interact in the air in a chemical reaction catalyzed by sunlight.

The primary ozone precursors are volatile organic compounds, or VOCs, which are emitted from countless sources—including oil refineries, gas stations, wildfire, paints, even personal care products, like deodorant—and nitrogen oxides, or NOx, a product of combustion.

“Photons are needed to break up certain molecules, so the reactions typically will not happen without sunlight,” said John Lin, the associate director of the Wilkes Center for Climate Science & Policy. “It essentially chops up those chemical bonds. Then ozone reacts with other things and levels get lower at night.”

To effectively combat ozone pollution, the state needs to know which pollutants are driving the problem.

“A big question DAQ has deal with is do we reduce NOx or do we reduce VOCs?” Ling said. “Policy is important. Which lever do you pull? If you pull the wrong lever you can increase ozone.”

Lin and Hallar oversee a collection of air quality measuring instruments atop the Browning building on the U campus, as well as a network of fixed sites around the valley and mobile equipment on TRAX trains.

“Emissions are linked in various ways. For example, things that emit methane emit other things like NOx, which leads to ozone,” said Lin, who has long studied Utah’s greenhouse gas emissions. “This is an opportunity where understanding ozone can also lead to an understanding of greenhouse gases and fugitive emissions.”

Other important factors affecting Salt Lake Valley’s ozone levels are its valley terrain, hemmed by the Great Salt Lake and mountain ranges cut by deep canyons. This terrain in turn shapes air currents and weather patterns that also play a role.

This is why it’s crucial to take measurements far above the ground and observe how ozone levels move around far off the ground, according to Carrie Womack, a researcher with the NOAA Chemical Sciences Laboratory based in Boulder, Colorado.

“Ozone on the ground is what affects human health,” Womack said,” but the atmosphere has this complicated, dynamic, vertical structure to it, and it is important to know what’s above.”

Through August. 8 the NOAA team will fly a Twin Otter aircraft for a total of 70 flight hours, taking ozone measurements and air samples at various altitudes around the valley. Another instrument located at fixed site during the project uses lidar to generate a constant vertical profile of ozone levels extending into the atmosphere above Hawthorne Elementary School, the site of a DAQ monitoring station.

Womack’s crew is also driving a sprinter van packed with state-of-the-art instruments around the valley, taking measurements for different kinds of NOx and up to 60 different VOCs. Such compounds number in the hundreds if not thousands, but the team has identified this large subset to focus on.

“This is really a multifaceted campaign because we are coming with our assets and the University of Utah has its assets, and by combining efforts and sharing data, we can build a more complete understanding of what’s going on,” Womack said. “The more data you have, it’s more than the sum of its parts. If you just took one instrument’s measurements, that’s great. But it helps to have it in the broader context of the entire atmosphere.”

• Theo Stein NOAA Communications
  ‭(303) 819-7409‬ theo.stein@noaa.gov
• Brian Maffly Science writer, University of Utah Communications
  801-573-2382 brian.maffly@utah.edu
• John Lin Department of Atmospheric Sciences
  ‭(801) 349-0831‬ John.Lin@utah.edu
• Gannet Hallar Professor of atmospheric sciences
  Gannet.Hallar@utah.edu