A relentless wave of dry heat, coupled with a recent outbreak of wildfires, is fueling a summertime scourge of the Intermountain West: the near-daily spikes in ozone and other air pollutants, collectively known as smog.
Colorado’s Denver metropolitan region and Northern Front Range — which extends from about the Wyoming border to Boulder — have been breaching federal ozone standards for years, despite vast improvements in controlling emissions in both transportation and the energy sector.
Experts attribute the continued seasonal surges in this colorless gas, which affects respiratory and cardiovascular health, to a combination of factors: climate change, population expansion and the region's unique geography.
"There have been a lot of efforts to reduce pollution through making cars cleaner, through better regulations of oil and gas," Anthony Gerber, director of pulmonary research at National Jewish Health, told The Hill.
"At the end of the day, we're only treading water because of issues with climate and then the growth of the Front Range," Gerber said.
Different from the atmospheric ozone layer, which protects people from solar radiation, ground-level ozone poses a potential threat to those who inhale it, especially among individuals with existing sensitivities.
This type of ozone forms when pollutants like nitrogen oxides or volatile organic compounds — known collectively as "ozone precursors" — react in sunlight and heat, according to the Colorado Department of Public Health and Environment.
Those compounds can come from vehicles that run on gasoline, industrial emissions, oil and gas operations and the particulate matter in wildfire smoke. The precursors then "mix the atmosphere with UV light and heat to create ozone," Gerber explained.
The highest ozone levels in the region are not typically in the middle of an urban center; rather, they are usually "more nestled up against the Front Range foothills," according to Gerber.
"Because of the mountains, those precursors can get trapped," he said. "But in periods of unusual weather — hot, dry weather, without a lot of winds — you can actually wind up with higher ozone levels that more broadly impact the urban areas."
This summer has featured persistent dryness and an influx of smoke over the past couple weeks from wildfires thousands of miles away and a series of local blazes.
Mike Silverstein, chair of the Regional Air Quality Council, explained that while the region does have prevailing winds that flow from west to east, the mountain range blocks the airflow at ground level.
Silverstein described a daytime "bathtub effect" in which warm air rises uphill and ushers in a mix of "all the oil and gas emissions, all the urban emissions, all the consumer products — hairsprays and bathroom products and cleaning products, paints and solvents, auto exhaust."
"Then the sunlight causes the reaction of these various pollutants to become ozone," said Silverstein, whose agency advises the state on air quality for the Denver metropolitan/North Front Range nonattainment region.
"It kind of puts a cap on our region — it’s like a dome," he added.
Despite the incessant air quality alerts this summer and in recent years, Silverstein said "ozone levels and the number of ozone exceedance days tends to be fewer in recent years than we experienced 20 years ago."
Attributing that decline to a significant reduction in emissions, he explained that Environmental Protection Agency (EPA) ozone attainment thresholds have become increasingly stringent.
That said, Silverstein stressed that the region endures ozone standard exceedances for at least 30 days each year. Every summer, he continued, conditions also vary based on meteorological factors.
As far as current surges are concerned, Silverstein pointed to the wildfire smoke — not just from local blazes, but from those in Canada and California — as "a big confounding factor."
Until the fires began to flood the region with smoke in the past couple weeks, Silverstein said he observed "plenty of exceedance days" for ozone, but individual numbers weren't necessarily as high as in recent years.
"Then when we started seeing the wildfire impact, the numbers just shot up," he added.
For Gerber's patients, many of whom already have diminished lung function, the persistent pollution has meant an increase in symptoms like chest tightness. Due to the inflammatory nature of such pollutants, Gerber also voiced concern about the potential for related strokes or heart attacks.
"We really encourage people to make sure they're taking all of their cardio-protective medications when the pollution is spiking," Gerber said.
Although Rocky Mountain foothills inhabitants may suffer from a routine summer spike in air quality issues, they are hardly the only residents of the U.S. West to endure such seasonal circumstances.
Silverstein cited Los Angeles as a prime example of a place marked by such pollution, noting that the "trapping effect" of mountainous topography helps drive the accumulation of contaminants.
Meanwhile, a recent study recently connected oil and natural gas development to summertime surges in ozone levels at New Mexico's Carlsbad Caverns National Park. Contaminant concentrations there often surpass EPA standards, as pollutants blow in from the Permian Basin, the authors found.
Gerber also flagged Salt Lake City as a vulnerable place and characterized ground-level ozone as "a general regional problem,” which also includes other pollutants, such as the particulate matter unleashed by wildfires.
"The two things tend to travel together," he said, noting that this mix of ozone and particulates is conventionally known as "smog."
Looking back at a past in which oil and gas were dominant contributors to Front Range air pollution buildup, Gerber recognized the regulatory progress that has helped mitigate those emissions.
"But now we're facing the dual problems of hotter days and also wildfires," Gerber said. "The evidence suggests that our air quality for the next 10 to 20 years is going to continue to frequently be at these sorts of unsafe levels."
Rather than relying on regulation to solve the problem, Gerber stressed a need to develop resilience strategies and modify the behavior of residents in areas impacted by ozone, such as exercising at earlier times of day.
Silverstein echoed these sentiments, adding that "it comes down to lifestyle choices" — making the decision to minimize the use of petroleum-based products, switching from gasoline- to electricity-powered lawn tools and reducing time spent driving.
The Regional Air Quality Council is also proposing two bills that would impact oil and gas operators: one that would reduce emissions venting when wells are shuttered for maintenance, and a second that would require the recapture of certain pollutants.
Another potential solution that researchers recently explored was the possibility that free-fare public transit could make a dent in driving down ozone levels.
To do so, they assessed an August 2022 initiative in which the regional public transportation agency waived all fares, with hopes that voluntary shifts away from cars could reduce ground-level ozone.
But a University of Colorado Boulder PhD candidate, Grant Webster, who researched the effects of such shifts, recently determined they were insufficient. While Webster observed that public transit ridership during the period increased by 15 percent to 20 percent, car volumes stayed about the same.
For Colorado to see a 1 percent decline in ozone pollution, public transit usage would need to increase by 74 to percent 192 percent, he found, publishing the results in Transportation Research.
As the region continues to grapple with ozone and smog, Gerber emphasized the need for both short-term adaptive measures and longer-term actions that could reverse global warming.
"We can't wave a magic wand and put all the carbon pollution back into a bottle and get rid of it by next year," he said. "So we need to be smart about adaptive strategies that can minimize the risk for people who otherwise enjoy all the great things about living on the Front Range."
