Science Notes

What Are We Doing About Ozone on the Front Range

By Presley Church

July 20, 2021

RJ Sangosti, The Denver Post file

By now you may have seen the infamous “brown cloud” that sits over the Front Range during Colorado’s hot and sunny summer months- a visible reminder of the severity of Colorado’s poor air quality. Recently, Denver – the largest Front Range city – earned the notorious distinction of being the 7th worst city in the US for air quality. In fact, many counties throughout the front range have long failed Environmental Protection Agency (EPA) ozone standards. What is going on here? Let’s get into the details of ozone, nonattainment zones, and EPA regulations across the state.

What is Ozone?

Ground-level ozone is not caused directly. Instead, it’s created by chemical reactions caused by mixing Volatile Organic Compounds (VOCs) and Nitrogen Oxides (NOx) and, to some extent, Carbon Monoxide (CO). Considering that Front Range summers are full of sunlight, dry heat, and metro-area pollutants (motor exhaust, industrial and factory emissions, chemical solvents etc.) which cause VOCs and NOx, and the physical topography and air flows with mountains to the West which often trap such pollutants, it’s no wonder this part of the state has such an ozone problem.

Don’t get this confused with the ozone present in the earth’s stratosphere that protects us from UV radiation. This ground-level ozone is caused by pollutants and comes with health effects. With ozone, the helpful adage you may wish to remember is ‘good up high, bad nearby’.

What’s the concern?

The Air Quality Control Commission (AQCC) and EPA are primarily concerned with the human health hazards that come with ozone exposure. The following are health risks: respiratory irritation, lung inflammation, asthma and chronic lung disease aggravation, lung damage, and other lung-related effects especially among younger and older demographics. 

What action is being taken?

Since 1971 the EPA has used their National Ambient Air Quality Standards (NAAQS) to gauge what actions may be required for better air quality. The Denver Metropolitan Area (Adams, Arapahoe, Boulder, Denver, Douglas, and Jefferson counties) often fails these safety standards and therefore has been designated an ozone nonattainment zone. The regulations of such zones have changed overtime: In 1997 the EPA NAAQS was set at .08 parts per million (ppm) over 8 hours, nicknamed the 8-hour standard. In 2008, the EPA decided that additional protection was required and the standard was changed to 0.075 ppm over 8 hours. Yet again in 2015 this NAAQS was changed to 0.07 ppm over 8 hours.  These standards use air quality data from monitoring sites acquired over 3 year periods. 

What does this mean in Colorado?

Denver, Boulder, Greeley, Fort Collins and Loveland are included in Colorado’s nonattainment areas typically with an 8-hour Nonattainment Zone classification of serious (the scale ranges from marginal to extreme).  At times the Denver-metro area is reported to have surpassed the advised .07 ppm over 8 hours. 

US Environmental Protection Agency

Recently, the county commissions of Boulder County, the Center for Biological Diversity, and other supporting environmental groups brought a lawsuit against the EPA for excluding northern Weld County from the nonattainment map, and this went to the US Court of Appeals for the District of Columbia Circuit.  The court sided with Boulder County, calling on the EPA to review Colorado’s nonattainment area.  On Wednesday, May 26th the EPA voted that Weld County should be included in the nonattainment zone.

In response, Weld County Commissioners are encouraging citizens to fight back against these proposed regulation changes. They argue that this conflicts with the 2008 and 2015 nonattainment standards that are still in place. The Weld County Website states that 

“the data in the record have not changed since U.S. EPA first issued their decision. Further, more recent data gathered and analyzed by independent consultants for Weld County have come to the same conclusions that the state of Colorado made: the interaction of weather, topography and emissions in northern Weld County do not contribute to ozone by violating monitors on high ozone days.” 

Because nonattainment zones require regulation on oil and gas production sites and other polluters, it makes sense that a county as dependent on such industries like Weld would push back on new standards. Part of The D.C. Circuit Court of Appeals’ reasoning in requiring the EPA to review Weld County was because they needed to further account for the “ozone-creating potential of oil and gas operations across the entire county,” according to the Colorado Sun.

The EPA opened a 30 day window for public comment which closed on July 14, 2021. Additionally, Colorado officials were given 120 days to provide more information to change that decision. 

Stay tuned for updates on the Colorado nonattainment zone as the EPA finalizes their decision. 

In the meantime, you can subscribe to our newsletter to stay up to date on Science Notes like this one and all things science-policy in Colorado. 


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