The U.S. Environmental Protection Agency has given Utah three years to reverse a trend of rising ozone pollution in some of its most populated counties.

The EPA on Tuesday formally declared portions of seven Utah counties to be in violation of national standards for ozone, an airborne pollutant that is particularly harmful to children. The long-anticipated determination creates “nonattainment areas” — geographically defined regions with potentially harmful pollution levels — spanning Salt Lake and Davis counties, as well as parts of Weber, Tooele, Utah, Uintah and Duchesne counties.

“Following the data and the law, today’s designations reflect continued progress in addressing ground-level ozone and its precursors,” EPA Administrator Scott Pruitt said in a written statement announcing the Utah decision. “EPA will continue to work closely with our state and tribal partners to improve air quality for all Americans.”

But because these areas exceed federal limits for ozone by relatively small margins, the EPA has classified the regions as “marginal” nonattainment areas, meaning Utah will have three years to monitor the situation before its regulators will be required to draft plans for curbing the pollutant.

Utah’s decadelong struggle to comply with federal standards for small particulate pollution, which typically accumulates during winter inversions, is well-known. Ozone, however, is a relatively new problem in the Beehive State.

Invisible risk

Ozone pollution has increased to concerning levels on the Wasatch Front only in recent years, said Bryce Bird, director of the Utah Division of Air Quality. At the same time, the EPA decided to lower the levels of ozone considered acceptable at ground level, where humans might be exposed to it, from 75 parts per billion to 70 parts per billion — in light of growing evidence that the pollutant is more harmful than previously thought.

Compliance with the EPA standard is determined by averaging the fourth-highest ozone levels measured over the course of three years. According to the Utah Division of Air Quality, an air-quality monitor in Bountiful averaged 76 parts per billion in 2016.

Ozone is a colorless, odorless gas that can effectively burn sensitive lung tissues when inhaled, leaving scarring and potentially permanent damage. The pollutant can trigger symptoms such as coughing and shortness of breath, and it worsens and may cause diseases such as asthma and chronic obstructive pulmonary disease, or COPD.

Children are especially at risk because repeated ozone exposure is thought to have a cumulative effect. Athletes and those who recreate outdoors are also considered at risk due to an increased chance of ozone exposure on warm, sunny days.

Unlike most other air pollutants, ozone is not emitted directly but instead forms in the atmosphere when sunlight triggers reactions involving key chemicals such as nitrogen oxides and volatile organic compounds. These precursors, as they are called, come from a variety of sources, but are typically associated with vehicle emissions.

Computer simulations built by the EPA suggest the Wasatch Front is already on track to meet the new federal ozone standards by the 2021 deadline, Bird said. Increasingly strict rules for vehicle emissions imposed at the federal level, combined with the prospect of introduction of cleaner-buring fuels in Utah, should help reduce ozone formation in Utah’s most populous counties.

In addition, the state Division of Air Quality has already created rules regulating products that emit volatile organic compounds, which are also thought to contribute to Utah’s particulates problem. With these already in place, Bird said, air quality on the Wasatch Front should continue to improve despite recent trends.

Summer blues

Warmer, drier summers have caused ozone to accumulate on the Wasatch Front more frequently, Bird said. Some parts of the state exceeded the federal ozone standard 30 to 40 times last year.

Typically, the summer rainy season helps form afternoon thunderstorms in July and August, creating cloud cover that disrupts the formation of ozone, Bird said.

Change in the state’s weather patterns, he said, “is a concern … but it’s the one thing we have absolutely no control over.”

The situation in Uintah and Duchesne counties is more difficult, Bird said. Current computer models do not indicate conclusively the area will attain the EPA ozone standard within three years, because the nature of the problem in the Uinta Basin is more complex.

The eastern Utah basin is among few known areas to experience ozone formation in the winter, a phenomenon thought to be linked to emissions from the region’s oil and gas operations.

The Utah Division of Air Quality has sought to crack down on emissions from the industry in the area, Bird said. State regulators require even small oil and gas wells to obtain air-quality permits — even when their operation would not normally require that step elsewhere. Oil and gas operators also must install the best available emission controls to operate within the basin.

Environmental groups have acknowledged Utah’s efforts to address the Uinta Basin’s ozone problem, but some, including the New York-based Environmental Defense Fund, worry the state and the EPA haven’t gone far enough.

“By implementing simple, straightforward pollution standards for oil and gas sector, the state of Utah and the Environmental Protection Agency can deliver major clean air benefits for people in Duchesne and Uintah counties,” Jon Goldstein, director of regulatory and legislative affairs for the Environmental Defense Fund, said in a written statement.

“The Utah Department of Environmental Quality has made gains in recent months to update the state’s oil and gas policies,” Goldstein continued, “but this progress must continue to restore healthy air quality to Utah’s families.”

The Center for Biological Diversity also raised concerns in a Tuesday statement that the Bureau of Land Management has continued to issue leases to oil and gas operations in Uintah and Duchesne counties, despite known issues with ozone in those areas.

But Utah’s ability to address the situation is limited, Bird said. About 80 percent of the oil and gas sources in the Uinta Basin are on federal or tribal lands where the EPA, rather than the Division of Air Quality, has jurisdiction.

Bird said the EPA is expected to put requirements in place similar to Utah’s in Uintah and Duchesne counties in the near future.

Meanwhile, Bird advised residents to stay apprised of air quality conditions — even during the summer. Current conditions can be checked at air.utah.gov.

Officials recommend avoiding physical activity during the afternoon, when ozone is most likely to peak, and also ask residents to decrease emissions by limiting driving, avoiding excessive use of gasoline-powered tools such as lawn mowers, and choosing paints and cleaners that emit fewer volatile organic compounds.