• Original Reporting
  • Sources Cited
  • Subject Specialist
Original Reporting This article contains new, firsthand information uncovered by its reporter(s). This includes directly interviewing sources and research / analysis of primary source documents.
Sources Cited As a news piece, this article cites verifiable, third-party sources which have all been thoroughly fact-checked and deemed credible by the Newsroom in accordance with the Civil Constitution.
Subject Specialist This Newsmaker has been deemed by this Newsroom as having a specialized knowledge of the subject covered in this article.

Smoke from West Coast wildfires in 2021 caused half of Colorado’s toxic ozone violations on the summer days that repeatedly breached EPA standards, according to a new study led by the National Oceanic and Atmospheric Administration. 

Smoke from Canadian wildfires obscures downtown Denver and most of the Front Range, from the Mother Cabrini Shrine above Golden, on May 22, 2023. The haze has contributed to danger alerts for unhealthy air in late May. (Michael Booth, The Colorado Sun)

The findings will give ammunition to multiple parties in the ongoing battle to define the worst contributors to ozone pollution and consider new limits on Colorado’s oil and gas industry or Front Range drivers. 

The study’s authors and clean air advocates say the EPA does not relax its vigilance for ongoing ozone violations just because the totals were influenced by outside sources like fire smoke. They say Colorado regulators should consider speeding up actions on locally produced ozone the state can control, to protect health and avoid new federal sanctions. 

Trade groups, meanwhile, point to increasing wildfire smoke and Colorado’s high naturally produced background ozone as evidence that state regulators should not choke off economic activity to please the EPA if such rules can’t realistically lower ozone levels. 

“People might want to throw up their hands and say, ‘Oh, we can’t do anything about anything. So we should do nothing.’ But I think the opposite is true,” said Andrew Langford, a researcher with the NOAA Chemical Sciences Laboratory in Boulder and lead author of the smoke study. 

“It just makes it that much more important to try to control the ozone we can control. It’s still bad for people,” Langford said. “Every extra bit that you can reduce it will be a good thing.”

The standards could get even tougher for Colorado in coming years, Langford said. The EPA is reconsidering some of its National Ambient Air Quality Standards, and a key science advisory group is likely to recommend lowering the ozone standard to 55 to 60 parts per billion averaged over an eight-hour period, Langford said. With “background” or natural ozone hovering around 50 on many days in the Denver metro area, he added, before accounting for the additions from wildfire smoke, Colorado is “not even getting close” to meeting EPA demands. Ozone monitors on the Front Range have shot above 80 on many days in recent years, after declining in previous decades.

The NOAA study combined ambient air measurements from regulatory and private monitors in Colorado, using 2021 readings. The researchers also had lidar, or laser light studies, that detailed the extent and makeup of fire smoke plumes drifting from massive 2021 fires in Arizona, California and the Pacific Northwest. The study, co-authored with researchers from the University of Colorado, was recently published in the “Journal of Geophysical Research.” 

The north Front Range nonattainment area for ozone, which includes nine counties from Larimer on the north to Douglas on the south, saw a record number of ozone violations in the summer ozone season of 2021. In July, ozone violations hit on two-thirds of the days, Langford said. The NOAA analysis shows wildfire smoke caused about 8 parts per billion of the ozone on some July days when the toxic gas was often spiking above 80 ppb, compared to the current EPA limit of 70 ppb. 

On some days of 2021, the wildfire smoke contribution was as high as 12 ppb, the study said.

“And probably about half of those violations would not have happened without the wildfire smoke,” Langfor said. “The smoke doubled the number of violations, basically. Over the course of the summer, the smoke pushed ozone up by an average of three or four parts per billion a day, which is pretty substantial.”

To put that in context, Front Range officials are considering seeking a ban on the sale of new gas-powered lawn mowers and leaf blowers, because that small-engine category contributes about 2.5 parts per billion on many summer days. Clean air advocates argue Colorado must do a better job trimming ozone in places where it has some local control, no matter how small a portion of the total ozone, since bad wildfire years are inevitable and the EPA standards are likely to get more strict.

The NOAA study comes as environmental watchdogs point to 2023 ozone readings that already guarantee Colorado will be above the 2021-23 averages that will trigger the EPA to move the Front Range counties from a “moderate” violator of the 2015 limits to a “serious” violator. Colorado needed to keep its highest 2023 readings in the 40 ppb range to avoid triggering the downgrade, but the monitors have already recorded ozone in the 80s in May. The state issued another high ozone alert for Tuesday.

Those advocates want state health regulators to ask the EPA to make the downgrade now, instead of waiting until 2024 deadlines and delaying ozone action by the Air Quality Control Commission. Each downgrade requires Colorado to meet a new set of EPA ozone requirements, including expanding the number of oil and gas and other industrial operations that must seek state pollution permits. 

The state Air Pollution Control Division, which staffs and makes recommendations to the commission, said a number of initiatives in recent years will help cut both ozone-causing emissions and greenhouse gases that contribute to climate change. Those include requirements for an overhaul of new car and heavy truck sales to cleaner electric models, and working with the Colorado Oil and Gas Conservation Commission to lower emissions from oil production. 

Local elected officials working with environmental groups want more action, and faster, including a pause on oil and gas drilling in summer months where heat helps produce excess ozone, and more spending on transit. 

Oil and gas officials, meanwhile, said the smoke study should influence the work of an interim ozone study committee set up by the 2023 legislature to consider new policies. 

“The data from this NOAA analysis is revelatory and underscores the need to holistically study and ultimately address the Front Range’s ozone challenges,” said Kait Schwartz, director of API Colorado. Regulators should look at all influences on ozone “rather than squeezing a single industry in an effort to score political points,” Schwartz said.

The layers of EPA ozone regulation for Colorado can be confusing, but the state is in violation of all of them.

Last year, the EPA downgraded Colorado from “serious” to “severe” violations of the 2008 standard of 75 ppb for ozone. The state must submit detailed plans to lower ozone to the EPA each time there is a downgrade. Colorado in late 2022 submitted only part of its latest implementation plan and delayed the rest, after discovering that its calculations of ozone contributions from oil and gas severely underestimated emissions. 

When the EPA moves Colorado to the “serious” category for its lowered 2015 standard of 70 ppb, it starts the clock ticking on state regulators writing yet more implementation plans for compliance. Colorado officials said last week they were considering the idea of asking for that downgrade earlier than required, but had not made a decision.  

The complications from wildfire smoke contributing to ozone are amplified when Colorado’s normal weather patterns are disrupted, the NOAA researchers said. On hot summer days, Front Range ozone often peaks under late afternoon sunshine, and the accumulation of transportation and oil and gas emissions in the trough between the plains and the foothills. 

The ozone is usually dispersed, though, by afternoon and evening thunderstorms that blow and wash out contaminants. That pattern can cut an ozone spike from the threshold eight hour average down to four or six hours, avoiding the EPA’s trigger points, Langford said. 

In 2021, as wildfire smoke blew into Colorado, the summer weather pattern changed for unrelated reasons, Langford said. The afternoon storms from the west didn’t appear, often replaced by upslope winds from the east that kept pushing the contaminants up against the foothills monitors. 

“It didn’t get blown out to Kansas,” Langford said. 

The EPA’s ambient air standards do allow for communities to claim an exemption if they can prove ozone violations were caused by one-off events, or were limited to one- or two-day violations with little chance of repeating, Langford said. With Front Range readings worsening for years now, he said, it’s unlikely Colorado would qualify even if state leaders made the politically unpopular decision to seek exemptions. 

“It’s not set up to exclude two-thirds of the days in a month,” he said. 

Michael Booth is The Sun’s environment writer, and co-author of The Sun’s weekly climate and health newsletter The Temperature. He and John Ingold host the weekly Sun-Up podcast on The Temperature topics every Thursday. He is co-author with...