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Some of the worst ozone pollution in the U.S. settles along the Front Range. New rules to fix it are ahead.

Colorado has made some progress toward reducing the chemical dangerous to human health. But it will take leaning on automobiles and oil and gas producers to really move the needle.

Traffic on Interstate 25, Wednesday, May 19, 2021, in Denver, CO. (Hugh Carey, The Colorado Sun)
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When it comes to oxygen, the Front Range sometimes has too much of a good thing. On many sunny, summer days the region has not only O2 in the air but also O3 – oxygen with an extra atom that transforms it into a corrosive gas — ozone.

“The extra atom of oxygen turns it from an essential to something dangerous to breathe,” said James Crooks, a researcher at National Jewish Health in Denver.

Ozone has been the bane of state air quality regulators for two decades as they have tried to curb the ingredients – volatile organic chemicals and nitrogen oxides, or NOx – that create it.

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Over that time, the region’s designation has slipped from the Environmental Protection Agency’s marginal nonattainment designation to moderate and then to serious. And if the nine-county Front Range isn’t in compliance by July, it will be downgraded once more to severe, triggering a new round of regulations and a clamp down on new emission sources.

“We are going to be downgraded to severe unless something magically happens,” said Mike Silverstein, executive director of the state Regional Air Quality Council , which is responsible for putting together a plan to reduce ozone to safe levels.

The state’s new implementation plan, or SIP, however, drew fire from environmental groups for being inadequate, even before it was submitted in March to the EPA, which oversees compliance with federal clean air standards.

“The EPA should not approve the plan,” said Robert Ukeiley, an attorney with the Center for Biological Diversity. “If they didn’t, it would give the EPA the power to create its own plan or the state would have the opportunity to improve the plan.”

Some progress on ozone is better than none. But still.

For years, ozone has hung over a litany of community clean-air battles, from the fight by Boulder residents to close Xcel Energy’s coal-burning Valmont Station (the coal-fired unit was shut in 2017) to the push by Broomfield homeowners for tighter controls on local oil and gas drilling to the current neighborhood opposition to renewing the air permit of the Suncor refinery in Commerce City.

Denver ranked eighth in the country for worst ozone pollution in the American Lung Association’s 2020 pollution assessment. Fort Collins ranked No. 17.

The Front Range’s slide, however, belies the progress that has been made in cutting pollution, with a 44% reduction between 2011 and 2020 in volatile chemical emissions to 293 tons a day, and NOx down 49% to 164 tons per day during the same period, according to RACQ figures.

“We are making progress, but not fast enough,” Silverstein said.

Part of the problem comes from the federal government repeatedly dropping the level of ozone in the air that is considered safe as medical research has found it dangerous at lower and lower concentrations.

The health standard for ozone, set under the federal Clean Air Act, fell from an average of 80 parts per billion (ppb) over an 8-hour period in 1997 to 75 ppb in 2008 and then to 70 ppb in 2015.

“We aren’t even close to meeting the 2008 standard, much less the 2015,” said Alexandra Schluntz, an attorney for the environmental group Earthjustice. “The proposed SIP is not sufficient for attaining the 2008 standard.”

Of course, even reaching the 2015 standard would be cold comfort since there is growing evidence that ozone poses a risk even at lower levels.

“The scientific consensus is that the current standard isn’t sufficiently protective, and that it should be decreased to 65 ppb or lower,” said Crooks, the National Jewish researcher.  

To get a better handle on the Front Range’s ozone problem there are three fundamental questions that need answering: Why is ozone so dangerous? Where does Front Range ozone come from? And what is being done about it?

Why is ozone so dangerous?

When the ozone levels are above the health standard – on hot, sunny summer days with calm weather conditions – everyone is breathing in the gas, though once it is in the body, where it goes and what it does varies from person to person.

“That third oxygen is very reactive,” said Anthony Gerber, a National Jewish pulmonologist and researcher on lung inflammation. “Oxygen doesn’t like to be O3. It wants to be O2. So, you breathe it in and that free oxygen molecule looks for something to oxidize.”

In the first instance, it can inflame lung tissue, but that’s just the beginning. “It damages cells and makes the body react to them, getting an immune system reaction,” Gerber said.

From there the effects can go systemwide. “That’s why it is unhealthy at any level,” Gerber said. “That inflammation for somebody who has heart disease might tip them to have an actual event.”

In healthy people, ozone has been shown to temporarily reduce lung function – which is why individuals are urged to refrain from outdoor activities like jogging on high-ozone days. But once the ozone dissipates, lung function returns.

“When you’re exposed to a short-term spike in air pollution you have an acute inflammatory response in your lungs that can temporarily make it harder for you to breathe,” Crooks said. “But when you’re exposed to air pollution constantly, even at relatively low concentrations, the inflammation spreads throughout your body and never lets up.”

This weighs particularly heavily on vulnerable populations, from infants to children to the elderly.

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One California study found that a 12-ppb increase in average daily ozone levels over the entire course of women’s pregnancy was linked to a 47.2-gram (1.7 ounce) reduction in newborn birth weights. “This association was most robust for exposures during the second and third trimester,” the University of Southern California researchers said.

Impact on birth weights is only the beginning.  “Young children are a vulnerable population with respect to air pollutants, given their narrow airways, higher breathing rate and developing lungs and immune system,” said a New York state study that tracked 1.2 million children from birth to age 6.

The study found that the risk of hospital admissions for asthma attacks increased 22% with a 1 ppb increase in average concentrations during the ozone season, and that children living in New York City were four times more likely to be admitted than children in other parts of the state.

Very young children were more susceptible and poorer children were found to have a greater risk of asthma-related ER and hospital admissions than others at the same ozone level.

Studies in Texas and Seattle also found some association between increased ozone levels and childhood asthma.

Long-term exposure to ozone pollution is likely one of the causes of asthma and an exposure over eight hours between 31 ppb and 50 ppb can lead to an increase in hospital admissions and emergency room visits, according to the EPA’s 2020 ozone science assessment.

In a study of people over age 65, Harvard School of Public Health researchers found a 10 ppb daily increase in the ozone warm-season was linked to an increase in deaths. The increase was small, less than 1 death per million people at risk, but statistically significant.

“This risk occurred at levels below current national air quality standards, suggesting that these standards may need to be reevaluated,” the study said.

Nor are the risks limited to the elderly. Researchers from Yale and Johns Hopkins universities looked at mortality in 95 urban communities and found that a 10 ppb increase in the previous week’s ozone levels was associated with a 0.52% increase in daily mortality and a 0.64% increase in cardiovascular and respiratory mortality.

“The risks are small, but you have to be concerned about apparently small risks, because millions of people are exposed across the United States,” said Jonathan Samet, dean of the Colorado School of Public Health.

All these epidemiological studies looked at ambient ozone levels and real populations, but the impacts of ozone may be even more far-reaching, according to emerging laboratory research, as ozone pollution can set off stress hormones, compromise liver function and exacerbate diabetes.

“The initial events in the cascade of physiological events include sensory nerves in the respiratory tract and respiration tract inflammation,” the EPA’s science assessment said. “These early physiological reactions to ozone may trigger a host of autonomic, endocrine, immune and inflammatory responses throughout the body at a cellular, tissue and organ level.”

And yet, even though ozone is the second most dangerous pollutant regulated under the Clean Air Act, after fine particles like soot, it evokes little public consternation.

“One of the major problems is people don’t see it, don’t smell it. It is silent,”  Gerber, the National Jewish doctor, said. “When someone shows up in the health care system, it isn’t like the doctor is going to write on the chart: increased risk from ozone. They are going to treat your asthma without realizing that the flare-up was caused by ozone.”

Where does the Front Range’s ozone come from? 

Ozone isn’t a pollutant emitted by a specific source, like sulfur dioxide coming out of a power plant smokestack. It is created in the air as a mélange of chemicals interact with summer heat and sunlight.

The photochemical transformation of those volatile organic chemicals and NOx into ozone is the result of hundreds of thousands of chemical reactions taking place above the Front Range. Calm weather conditions are also a requirement so the emissions aren’t simply blown away.

There is another layer of naturally created ozone more than 30 miles above the Earth’s surface that screens out the sun’s deadly ultraviolet rays. It is sometimes referred to as “good ozone.” 

It is when the gas covers homes, schools and playgrounds that it becomes “bad ozone.”

In the summer of 2014, the Front Range Air Pollution and Photochemical Experiment (FRAPPÉ), a collaboration of more than 100 scientists led by the Boulder-based National Center for Atmospheric Research, studied the drivers of summertime ozone pollution. 

The project collected data on Front Range sources of pollution, as well as meteorological and topographical data, from ground sites, mobile vans, balloons, lasers, aircraft and satellites.

The area examined included all or part of nine Front Range counties, stretching north from Douglas County to the Wyoming border, taking in Weld and Larimer counties and the cities of Denver, Boulder, Greeley and Fort Collins. This is the area the EPA has designated as the state’s ozone “nonattainment area.”

It has taken almost five years to analyze and model all the data collected that summer.

The project found that motor vehicles are the main source of NOx followed by the oil and gas industry – the two account for more than 60% of the emissions. Oil and gas operations are the leading generator of volatile organic chemical pollution, about three-quarters of all emissions, followed by industrial and motor vehicle emissions.

Frank Flocke, a scientist in the Atmospheric Chemistry Observations & Modeling Lab at the National Center for Atmospheric Research, poses for a portrait outside his facility in Boulder on April 21. (Andy Colwell, Special to The Colorado Sun)

Computer models used by RACQ put oil and gas at 41% of total volatile organic emissions in 2020.  Frank Flocke, an NCAR scientist and a lead researcher for FRAPPÉ, said his group’s work found oil and gas emissions were underreported in industry and state studies.

Estimates of annual reductions in oil and gas emissions also have been overly optimistic by as much as a factor of four, a recent study by University of Colorado and National Oceanic and Atmospheric Administration found. 

Xcel Energy’s coal-fired Comanche Generating Station, located in Pueblo, is the largest power plant in the state of Colorado. (Mike Sweeney, Special to The Colorado Sun)

Among the individual, large sources were the Denver International Airport, Xcel Energy’s Comanche Generating Station in Pueblo and the Suncor refinery in Commerce City.

The releases from Commerce City factories and the Suncor refinery are a highly reactive mixture of volatile organic chemicals that can create ozone much more quickly, Flocke said.

A state proposed Suncor permit renewal — which is being opposed by community and environmental groups — would allow the refinery to increase its volatile chemical emissions by 138 tons a year. 

The nature of ozone problems in many urban areas is pretty much the same. The emissions from autos and local industries build up over the day. The sun and heat cook them and ozone levels reach their peak in the late afternoon.

When the sun goes down the ozone dissipates and the process, if conditions are right, starts again the next day. 

Not so in Colorado.

“Sunshine and high pressure are the main ingredients as they are everywhere, but the Front Range has unique terrain and meteorology,” Flocke said.

What other metro areas don’t have is the Rocky Mountains, which can scramble the when and where of ozone formation, as well as the Denver Cyclone, a sweeping gyre of air that, from time to time, moves counterclockwise across the region.

On those hot, cloudless summer days, the pollutants not only bake over the Front Range but as the day warms the heat pushes the air and pollution upslope. “On days with strong upslope, the flow can reach the top of the Continental Divide by midafternoon,” according to a FRAPPÉ report.

The project measured ozone readings as high as 76 ppb along Trail Ridge Road in Rocky Mountain National Park and 78 ppb just off Colorado 7, north of the Longs Peak trailhead, at about 9,000 feet in elevation.

Prevailing westerly winds can push pollution from the mountains back down onto the Front Range and as the sun goes down, cooling air moves downslope, collecting nighttime pollution, which ends up pooling in the Platte River Valley. 

Under the right weather conditions, the pollution flows down from the mountains through Denver to Greeley, where it mingles with Fort Collins pollution streaming down the Poudre River Valley.

The pollution doesn’t necessarily stay on the east side of the divide. On a FRAPPÉ flight over the mountains, researchers using an array of chemical sensors detected high levels of ozone at Grand Lake, in Grand County.

 “We flew in the late afternoon and saw that the ozone was strongly elevated,” Flocke said. “The ozone was pushed over the Continental Divide by the upslope and then as the sun went down the downslope pushed it into the valley.”

The state Air Pollution Control Division has 14 official monitors that measure ozone pollution levels across the Front Range. Flocke said they ought to add another in Grand Lake “to see if this is a common occurrence.”

For the most part, the emissions in the southern portion of the nonattainment area, around Denver, are dominated by vehicles and local industries, while in the north oil and gas releases are the main pollution sources.

But another confounding factor is the Denver Cyclone — which, when it appears, can move pollution “primarily from oil and gas operations, from the north to the south leading to impaired visibility and air quality deterioration in the Denver metro area,” according to a FRAPPÉ  analysis.

“The ozone standard is tough to attain with our meteorology and terrain,” Silverstein said. “It makes our job really hard.”

What is being done about the ozone problem?

Even before the ignition of a single Front Range auto is turned on or a wisp of emissions escapes from an oil storage tank, the region has an average background ozone level of 40 to 50 ppb brought in on the winds from the west.

The EPA has an ozone monitor outside Crested Butte and, between 2018 and 2020, it averaged 67 ppb for the standard used to evaluate Clean Air Act compliance.

 “The background ozone has been increasing in the West, as a result of population growth,” Flocke said. “The wiggle room we have over that western background (ozone) is getting smaller and smaller.”

In 2019, Defend Colorado, a business advocacy group, argued that the state should seek an exemption based on this transboundary pollution, which can come from as far away as China. Gov. Jared Polis, however, rejected the notion and even balked at seeking a one-year waiver from the EPA.

“There’s too much smog in our air, and instead of hiding behind bureaucracy and paperwork that delay action, we are moving forward to make our air cleaner now,” Polis said in a 2019 statement.

And so, Silverstein said, “what we have to do is look at what’s left, though it doesn’t leave us much to work with.”

The state has played a game of regulatory whack-a-mole as the Air Quality Control Commission has issued rules to limit emissions from sources such as paints, wood coatings, foam manufacturing and personal-care products. If you can smell your deodorant or hair spray it is a source of volatile chemicals.

The RACQ even runs a program to encourage owners of gas-powered lawnmowers to trade them in for cordless, electric models. Residential mowing creates the equivalent of 5.5 tons a day of volatiles and 500 pounds of NOx.

The two big sources, however, remain the same.

“To make progress we will continue to have to focus on mobile sources and oil and gas,” Gary Kaufman, director of the state’s Air Pollution Control Division, said in an email.  “We will also be looking for opportunities to reduce emissions from the industrial sector.”

Nickel Road Operating’s Blehm Pad oil and gas development site is pictured west of Ault on May 19. (Andy Colwell, Special to The Colorado Sun)

Recently adopted limits on emissions for diesel motors used in the oil and gas industry and requiring zero-emission controllers, which operate equipment in the oil and gas fields, will also help, Silverstein said.

The Air Quality Control Commission is set to have rulemakings this year aimed at more emission reductions from the transportation and oil and gas sectors.

The proposed transportation rule, which is being developed, could require larger employers in the ozone nonattainment area to come up with plans to cut the percentage of workers who commute alone by doing things like charging for parking, and organizing carpools and offering shuttles from transit stops.

Other transportation initiatives could include mandating cleaner-burning gasoline and diesel fuels and tweaking emissions tests in the auto inspection and maintenance program, Silverstein said.

Nevertheless,  the tally, so far,  doesn’t add up to the needed reductions, according to Ukeiley, from the Center for Biological Diversity.

“We already knew from the data that the plan failed when the Air Quality Control Commission approved it in December,” he said. “The state keeps making these tiny little tweaks and we keep failing.”

The fact that companies self-report emissions and currently develop trip reduction programs without oversight weakens the overall effort, as does pressure to not hobble economic activity, Ukeiley said.

Environmental and community groups have sued the Air Pollution Control Division for what they called the “rubber-stamp” issuing of air emission permits to the oil and gas industry and allowing for “routine” gas venting. Three division employees filed a whistleblower complaint in March with the EPA Office of the Inspector General for what they said was a short-circuiting of pollution control analysis to expedite permits.

Despite the criticism and charges, Silverstein said, “as bad as it might sound, we are not that far off. We had an almost clean data year [in 2020], just two sites that didn’t make it, then the wildfire season came and blew everything up.” 

The state, however, doesn’t get cut any slack for natural disasters. “Attainment is attainment,” Silverstein said. The goal, he said, is to meet both the 2008 and 2015 standards by 2024 or sooner.

When the Front Range is designated a severe nonattainment area, it will force new requirements, such as additional penalties on companies for exceeding their permits and requiring reformulated gasoline in summer months to cut fumes from vehicles. Only nine areas in the U.S. are required to use reformulated gasoline: Los Angeles; San Diego; Greater Connecticut; Greater New York; Philadelphia-Wilmington; Chicago; Baltimore; Houston-Galveston; and Milwaukee-Racine.

It will lower the emission level at which new emitting sources, such as factories, must get a state operating permit to 25 tons-a-year of volatile chemicals or NOx from the current 50-tons-a-year. Existing facilities will have to show they are using “reasonable achievable control technology.”

To get a permit, new facilities will have to offset their emissions with reductions of existing emissions at a ratio of 1.3 tons for every ton emitted. For a serious nonattainment area, the ratio is 1.1 to 1.

“It is unlikely a new, large facility will locate here,” Silverstein said. One strategy would be to find a way to keep emissions below the 25-ton threshold or to create or buy offsets to keep emissions below that level.

EPA will evaluate the SIP section by section and approve it or return it to the state for revisions, said Carl Daly, acting director of the air and radiation division for EPA Region 8, which includes Colorado. The agency has 18 months to complete its review.

But even before EPA completes its review of the current SIP, the Front Range will fail to meet its July compliance deadline, and that will lead to reclassifying the region as severe, requiring a new and tougher SIP.

If the EPA does not approve the SIP, Colorado risks losing federal clean air funds and federal transportation funding, although it has been rare that those sanctions have been used.

“Basically, we are going to have two SIPs that say many of the same things,” Silverstein said.

Getting to attainment, however, is not the same thing as having clear air, for compliance is judged on the three-year average of the fourth highest ozone readings, not the highest.

On a hot and sunny afternoon on Aug. 27, as the temperature reached 87 degrees, monitors around the region logged well over the health standard: 78 ppb in Fort Collins; 82 ppb at Chatfield State Park; 83 ppb at Rocky Flats and at Boulder Reservoir; and 91 ppb in Golden.

“We are way behind the curve and it is getting harder and harder to catch up,” said Dan Grossman, the Environmental Defense Fund’s senior director for state advocacy.

At some point the pollution in the air may weigh more heavily on the Front Range, environmentalists and health experts say.

“Denver and the Front Range are an attractive place for people to move to,” National Jewish’s Gerber said. “When there is pollution and you can’t go outside it is going to make the place less attractive.”


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