Colorado finalizes stricter emissions rules to battle ozone pollution

Concentrations have exceeded EPA standards for more than a decade

By: - December 18, 2020 4:26 pm

The Suncor oil refinery in Commerce City is one of Colorado’s largest sources of air pollution. (Chase Woodruff/Colorado Newsline)

The Colorado Air Quality Control Commission on Friday finalized a new set of emissions rules aimed at bringing the Denver metro area into compliance with federal ozone pollution standards — but the region’s decade-long struggle with smoggy skies is expected to continue to run afoul of the Clean Air Act for years to come.

In a unanimous vote, AQCC commissioners approved revisions to the State Implementation Plan, or SIP, proposed by the state’s Air Pollution Control Division to achieve compliance with the Environmental Protection Agency’s 2008 ozone standard.

The adoption of the revised SIP, which includes stricter controls on oil and gas operations and other “major sources” of emissions, is a result of the EPA’s 2019 reclassification of the Denver region as a “serious” violator of EPA standards after more than a decade of noncompliance. Ozone concentrations in and around Denver this year repeatedly exceeded an eight-hour average of 80 parts per billion, above the EPA standard of 75 ppb set in 2008 — and well above the revised 2015 standard of 70 ppb.


Regulators at the APCD and the Regional Air Quality Council, however, say that those levels were inflated by the historic wildfires that Colorado experienced in 2020, and that modeling shows the state could be on track to achieve the 75 ppb standard by next year. The commission rejected several alternative proposals submitted by environmental groups challenging its use of modeling and requesting a voluntary downgrade to “severe” violation of Clean Air Act standards.

“We are appreciative that the commission acknowledged that many proposals were not sufficiently developed for consideration or adoption by the commission,” Lynn Granger, executive director of the American Petroleum Institute’s Colorado chapter, said in a press release. “Many did not demonstrate the emission reductions achieved or consider the potential economic impacts to existing and new businesses in the 10-county ozone nonattainment area.”

The Denver region’s ozone levels have declined slightly in recent years, but remain out of compliance with the two most recent federal standards. (AQCC)

For decades, Denver has struggled with high summertime concentrations of ozone, a hazardous pollutant that forms as a result of a chemical reaction between sunlight and precursors like nitrogen oxides and volatile organic compounds. Studies have shown that oil and gas operations and tailpipe emissions from gas-powered vehicles are the area’s largest sources of ozone precursors — though industry groups also argue that high levels of “background” ozone in the atmosphere, which can originate from as far away as China, make it difficult to address the problem through local pollution controls.

The bulk of the changes made by the revised SIP approved Friday relate to permitting and monitoring in the oil and gas sector. Colorado’s vehicle emissions inspection program already meets the requirements for a “serious” violation SIP, so no further changes were made.

The Denver region’s ozone levels have declined since peaking in the 1980s — the era of the infamous “brown cloud” — but still violate EPA standards and, scientists say, pose significant health risks to residents, especially sensitive groups.

“Denver is the 8th most polluted city in the U.S., and the entire metro region suffers from severe ongoing ozone pollution,” Denver City Councilman Jolon Clark said in a statement on the AQCC’s vote. “If you are an older resident of the region, the consequences are serious. If you are a young resident, with lungs vulnerable to ozone damage and disease, the consequences are serious. If you are a resident of the region with asthma, the consequences are serious.”

“Today’s decision was a step forward, but we need to do more,” Clark added.

Colorado ozone regulations under the Clean Air Act

The Environmental Protection Agency regulates air pollution across the country by setting National Ambient Air Quality Standards, or NAAQS — thresholds for various air pollutants beyond which additional state-level regulations are required.

NAAQS levels can be revised over time as scientists learn more about the health impacts of air pollution. In 2008, the NAAQS for ozone was set to an average of 75 parts per billion over an eight-hour period; in 2015, it was lowered to 70 ppb.

Areas that do not meet the NAAQS standards are designated by the EPA as being in “nonattainment.” Depending on how long an area has failed to meet the standards, it can be classified as being in marginal, moderate, serious, severe or extreme nonattainment.

In late 2019, a 10-county region in metro Denver was reclassified as being under serious nonattainment after failing to meet the 2008 ozone standard for over a decade. Higher levels of nonattainment require the enactment of stricter State Implementation Plans, or SIPs, which outline additional regulatory actions aimed at bringing the area into compliance with the NAAQS.

With ozone levels not declining fast enough, AQCC commissioners and state regulators expect the Denver region to be classified as a “severe” violator of the 2008 standard within the next several years — and it will soon become a “moderate” violator of the stricter 2015 standard, too. The APCD is already developing plans for stricter emissions rules that could be triggered when those EPA downgrades become official.

“It’s not been enough,” AQCC commissioner Elise Jones said of the state’s current emissions rules during Friday’s hearing. “We’ve been out of attainment for over a decade.”

“We need to keep coming back to the fact that unhealthy air has very real costs — in terms of people’s lives, their health, whether their kids have asthma, whether they go to the emergency room,” she added. “We should recognize that there’s an urgency behind this, because real people are hurt when the air is dirty.”


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Chase Woodruff
Chase Woodruff

Reporter Chase Woodruff covers the environment, the economy and other stories for Colorado Newsline.