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Ozone is the toxic air pollutant that has a lot of smart people on the Front Range really befuddled right now.

Colorado is making big cuts to greenhouse gases, mainly by closing coal-fired power plants even faster than expected. New laws, and old cars switched out for new ones, have made steep cuts to the amount of nitrogen oxide and volatile organic compounds emitted in the nine northern Front Range counties. 

But we’ve been getting worse, not better, in the past few years on ozone, that asthma-inducing gas cooked up by a combination of nitrogen oxide, volatile organic compounds, hot sunlight and wildfire smoke. We’ve had 38 Ozone Action Alert Days called already this year, with more to come before temperatures cool off. 

Remember that the EPA has now set the limit of average ozone at 70 parts per billion. And since we are regularly hitting ozone measurements into the 80s, the EPA is about to formally declare us in “severe” nonattainment of their limits. Here’s a chart that show where we’ve gone lately on ozone, in the zigzagging black line trending up, and where EPA says we need to be, below the green and red lines: 

The jagged line shows recent average ozone values on some of the worst days each year. The red line is where the EPA set the health standard for ozone in 2008, at a top limit of 75 parts per billion. The green line is the most recent EPA standard, as scientists cracked down harder on the respiratory hazards of ozone, at 70 parts per billion. (Regional Air Quality Council)

What can be done? The Regional Air Quality Council, charged with drawing up a plan to get below 70 ppb but with no power to enforce its proposals, put the dilemma in a chart for the Air Quality Control Commission, which does hold actual power to make law.

The northern Front Range “background” ozone level starts at 48.6 ppb, RAQC says. 

An at-a-glance view of why it’s been so difficult for the northern Front Range to cut its ozone production back below EPA limits. Our background ozone starts high, and the biggest places to cut elsewhere are partially walled off by special interests and consumer habits. (Regional Air Quality Council)

This is a favorite point of the oil and gas industry, which says it has already done a lot to tighten up its ozone and greenhouse gas-causing emissions. Should they be penalized for high background levels, trade groups ask? This background is made up of ozone blown here from Chinese coal plants, Los Angeles smog, wildfires, and even volatile organic compounds given off by “woody vegetation.” (Yes, we too thought woody vegetation was a good thing. But some plants have a mean streak, apparently.) 

There’s nothing we can do about that background amount, really, except pray for rain and fewer wildfires. And as the RAQC pointed out, metro Denver provides some of the “background” ozone for points east when prevailing winds blow that way. Apologies to Kansas City, but then you get the Chiefs and Patrick Mahomes. 

So what’s the next biggest chunk of ozone we can knock off? 

Back to you, oil and gas industry. Still a big target. At 8.6 ppb of that 70 ppb limit, regulators are likely to ask the industry to do more. Some environmental groups are promoting a summer pause on oil and gas exploration and production on the northern Front Range. 

Meanwhile, you drivers in your humble Toyota or Chrysler, did you think you were innocent? Cars and trucks are next on the ozone-producing chart, at 6.8 ppb. And the Great Switch-Out to cleaner electric vehicles is a very slow trickle compared to the EPA’s deadline for reducing ozone. So all of us driving fossil-fuel powered cars, or demanding that fossil fuel-powered trucks deliver us nice packages, will have to contribute at some point. 

Curtis Claar charges his Nissan Leaf electric vehicle at the EV Trail fast-charging station in Walsenburg, near Interstate 25. It took Claar nearly three years to make the Walsenburg station a reality. He hoped to have EV Trail’s second charging station in Colorado City online in early 2022. (Mike Sweeney, Special to The Colorado Sun)

Recently came the news that California is just going to ban gasoline cars altogether by 2035. We work on this for years, and California just tweets it out. Colorado has already adopted clean electric vehicle standards modeled after California, and in 2023 will likely pass clean truck standards modeled the same way. Will there be new pressure, given the size of California’s car market and influence, to speed up Colorado’s transition? 

Another category is an example of how tricky all this is: “Lawn & Garden.” Smoke-spewing two-cycle engines like lawn mowers and gas leaf blowers are a prime target of RAQC and other regulators. Some places are banning them. Others want expansive buyback or trade-in programs in favor of clean electric models. But that kind of legislation couldn’t even pass a Democratic-controlled Colorado statehouse this year

While the next step may not be obvious, RAQC executive director Mike Silverstein said, staring at this chart is a place to start. “It’s more information that helps us say, where do we want to spend our time,” he said.

Finally we present the ozone and emissions chart that is a true puzzle, so complicated (yet so colorful!) that the RAQC can’t help but return to it in its presentations to air pollution policymakers. 

This mashup graphic is a favorite of the RAQC. It shows some emissions dropping, while the ozone violations are recently getting worse, shown in the orange circles and squares at the top. (Regional Air Quality Council)

What this pickup-sticks view shows that baffles even the experts is that some of the key emissions that help create ozone are trending steadily downward. Daily nitrogen oxide and volatile organic compounds have steadily declined since 2010, according to the RAQC. 

Then look at the orange boxes with the 70s and 80s inside. Those are average ozone readings in parts per billion at key monitoring sites. Remember, the northern Front Range needs to get steadily down below 70 ppb in the next few years if it wants to avoid even more EPA-mandated sanctions. Those orange boxes are trending up. 

One reason for that is another factor on the chart, the burnt orange line of Daily Vehicle Miles Traveled. We may be driving ever-more-clean vehicles, but there are also more of us as the population grows, and we’re not cutting back our personal miles. 

Even with clean vehicle standards, Silverstein notes when presenting this chart, by the time everybody retires an older, dirtier vehicle, “you’re 10 or 20 years into the future time by the time you see the real emission benefits, because people like their cars, and they’re expensive, and they drive them and they hold on to them until it’s time to trade up.” 

And what about climate change, policymakers want to know? Are hotter and sunnier days on the Front Range, with average temperatures demonstrably creeping upward, also making those ozone numbers worse and negating the impacts of past policy choices? 

“There is a climate impact on ozone,” Silverstein said, adding that National Jewish Health is conducting some of the best research to prove it. Laughing that the researchers “will kill me” for summarizing too breezily, Silverstein said, “it’s a couple of parts per billion penalty for a warming climate.”

As these charts cumulatively show, just a couple of parts per billion is, scientifically speaking, a lot. 

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Michael Booth

Michael Booth is a Colorado Sun reporter covering health, health policy and the environment. Email: booth@coloradosun.com Twitter: