What Are Colorado’s Biggest Sources of Air Pollution?

While most of us were concerned with hail damage and the threat of more severe weather, Denver’s air quality worsened on Tuesday, May 28, nearing unhealthy levels on the Environmental Protection Agency's Air Quality Index scale. That doesn't bode well for the ozone levels the city might experience as temperatures continue to rise this summer.

After a couple decades of progress, Colorado’s air quality seems to be backsliding. Denver's notorious "brown cloud" made a rare reappearance in March, and a report last month from the American Lung Association found that the city's ozone problem is getting worse. And beyond localized air pollution, the city's greenhouse-gas emissions have remained flat for most of the last decade, preventing it from meeting many of its climate and sustainability goals.

Where's all this pollution coming from? Airborne pollutants come in many forms, many of which can be hard to track. But statistics maintained by the EPA through its National Emissions Inventory and Greenhouse Gas Reporting Program give us a pretty good idea of who the biggest individual culprits in Colorado’s worsening air-pollution problem are.

Comanche Generating Station, Pueblo

In the long run, no category of pollutant is more dangerous than greenhouse gases, and no facility in Colorado emits more greenhouse gases than the state’s largest power plant. Operated by Xcel Energy and located south of Pueblo, the Comanche Generating Station produces more than 1,400 megawatts of electricity through its three coal-fired generating units — resulting in the emission of nearly 9 million tons of carbon-dioxide-equivalent in 2017, according to EPA data.

In addition to carbon dioxide, the Comanche plant is also Colorado’s fourth-largest stationary source of nitrogen oxides and its fifth-largest source of sulfur dioxide, according to the most recent available EPA data. These so-called “criteria pollutants” are among the most common causes of ground-level ozone and other forms of smog.

But the biggest threat posed by coal plants like Comanche is the impact of their carbon emissions on the climate. Colorado’s ten largest emissions sources are all coal-fired power plants, and phasing out coal-powered electricity has become a priority for governments in Colorado and around the world. Xcel announced last year that it plans to retire two of Comanche’s generating units, in 2022 and 2025, respectively.

Suncor Energy Oil Refinery, Commerce City

Located just a few miles north of central Denver, Suncor Energy’s sprawling refining facility is the state’s largest non-coal-related source of greenhouse-gas emissions, but that’s only beginning. Much of the crude oil pumped out of the ground by Colorado’s booming oil and gas industry flows to Suncor’s plant to be refined into gasoline and other products, and the chemical cocktail that spews out of its smokestacks in the process includes some of the nastiest pollutants around.

The refinery releases an estimated 14.1 tons of hydrogen cyanide gas into the air annually, a test conducted last year showed. As reported by the Denver Post’s Bruce Finley this week, Suncor has requested an amendment to its state air-quality permit that would allow that figure to rise to nearly 20 tons. Hydrogen cyanide is a toxic gas that was deployed as a chemical weapon in World War I and used in gas chambers in Nazi Germany.

Suncor is also the state’s second-largest stationary source of fine particulate matter, a type of pollution consisting of microscopic airborne particles that poses a wide variety of risks to human health. It’s the fourth-largest source of volatile organic compounds, which lead to ozone formation and some of which are known to cause cancer. In short, for almost every major air pollutant tracked by the EPA, the agency’s data shows that the Suncor refinery ranks among the state’s top emitters.

West Elk Mine, Somerset

The state’s largest individual emitter of methane, an especially potent greenhouse gas, is one of its last active coal mines. While far less of it is released into the atmosphere every year, methane has more than eighty times the heat-trapping power of carbon dioxide, making it far more dangerous to the climate in the short term. (Atmospheric concentrations of methane have spiked over the last decade, and scientists aren’t entirely sure why.)

Tucked away in the Gunnison National Forest on the West Slope, the West Elk Mine vents more than 440,000 carbon-dioxide-equivalent tons of underground methane annually, according to EPA data. Unlike many oil and gas facilities, West Elk isn’t required to capture or flare its methane emissions, and in 2016, former governor John Hickenlooper supported operator Arch Coal’s request for an expansion of the mine, which could significantly raise its emissions levels.

Waste Management Denver Arapahoe Disposal Site, Aurora

If you’re a Denver resident, chances are that whatever you throw out in your trash eventually ends up at this landfill on the far eastern edge of the metro area, which takes in more than 3 million tons of waste annually. There, it’s processed and compressed, releasing particulate matter, and begins to decompose, producing methane.

Though the Denver Arapahoe Disposal Site utilizes gas-to-energy systems that collect and convert some of its methane into electricity, the landfill is still the state’s eleventh-largest emitter of methane and its single-largest stationary source of fine-particle pollution, according to EPA data.

EVRAZ Rocky Mountain Steel, Pueblo

The former Colorado Fuel and Iron Company is the state’s single-largest consumer of energy, hogging the lion's share of the power generated by the nearby Comanche station. It’s also a source of industrial pollution in its own right; according to EPA data, the EVRAZ facility is Colorado’s fourth-largest individual emitter of fine-particle pollution and its third-largest source of airborne lead.

Denver International Airport, Denver

The fuel burned by aircraft at DIA is, of course, a major source of greenhouse-gas emissions, but ground operations at the country's largest commercial airport by surface area are also a significant source of criteria pollutants. It's Colorado's second-largest individual emitter of carbon monoxide, fourth-largest source of volatile organic compounds, and fifth-largest source of nitrogen oxides, according to EPA data.

You and Me, Everywhere

Large industrial emitters do harm the state's air quality, but just as important are the collective impacts of consumer-level energy use, most notably in the transportation sector. Emissions from the vast network of well pads, tank batteries and compressor stations that make up Colorado's oil and gas supply chain, for example, account for as much as 40 percent of local ozone production on high ozone days in the metro area — but much of the rest can be attributed to motor vehicles. Cleaning up Colorado's air will require not just reducing pollution from a few dozen smokestacks scattered across the state, but addressing the millions of tailpipes that travel its roads every day, too.