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Here’s what you need to know about Colorado air pollution — and what you can do about it

A heat wave spikes ozone levels to “Unhealthy” on the Front Range, and Sun readers have questions. We sought some of the top air experts in the state for your answers.

Haze and smog shroud the mountain view behind the Denver City and County Building, as seen in a Nov. 5, 2019, file photo. (John Ingold, The Colorado Sun)
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The state has issued an ozone health warning for Coloradans every day since July 5. 

We’ve already accumulated 37 state Ozone Action Alert Days for 2021 by the last week of July, with plenty of scorching August and September weeks left to go, after tallying 43 all of last year. State officials are all but certain we’ll blaze past the 2020 total. 

We asked for your questions about how bad the air pollution is in Colorado this summer, and what, if anything, you can do about it. We’ve got some of the answers, after checking in with experts from National Jewish Health, Boulder County Health, the chief air quality meteorologist for the state Air Pollution Control Division, the National Center for Atmospheric Research, the EPA, and more. There were so many reader questions from Facebook, Instagram, Reddit and direct emails, that we’ll be taking on more in coming weeks. 

None of these expert sources are sugarcoating what’s going on this summer in Colorado. Pollution and high heat are creating problems almost daily for those with respiratory issues, and even for healthy people who exercise at the worst part of the day. So let’s get to your biggest concerns. 

Q: How can I tell how bad the air is in Colorado on a given day? What is the Air Quality Index, and how can I better understand what it means? 

A: The Air Quality Index is meant to be public-friendly, a system set up by the federal EPA and endorsed by state and local governments to give you one easily understandable number to react to. 

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The Index combines measures of a handful of pollutants, some of which are indeed a big problem in Colorado, some of which are big problems in other cities. One of the best explainers of the numbers is here. The local AQI draws data from a number of monitoring stations throughout the metro area and foothills, giving both real-time indicators and longer-term forecasts. 

You might want to bookmark colorado.gov/airquality, which in turn has many links to all kinds of useful real-time material and background information. Since ozone is the worry right now, look for the link to Ozone Action Day Alerts, and you can sign up there for emails when a new alert is issued. The EPA’s AirNow website is also a great bookmark

AirNow is also a free app available in all the smartphone app stores, and you can customize it with your ZIP code for the best information. 

air pollution ozone EPA AirNow
The EPA’s AirNow dashboard late in the day on July 28, 2021, showed dangerously high levels of ozone for the Denver area, with more bad days ahead. (Screen capture, Environmental Protection Agency AirNow)

Remember that many of the readings making up the AQI are for an 8-hour average. If you want more real-time information to help you make decisions — such as, “Should I go on a jog or fast walk today at 4 p.m.?” — EPA’s AirNow has a NowCast feature that looks at the last two to three hours, said Colorado Chief Air Quality Meteorologist Scott Landes. 

A basic rule is that at an AQI reading above 100, your local government puts air pollution warnings into the “unhealthy for sensitive groups” category, and it gets worse from there. Above 150 is just plain “unhealthy,” with two even worse categories beyond that. 

The components of the AQI include ozone, particulate pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide. Ozone is actually created when some of those other pollutants on the list combine and then get scorched under Colorado’s summer sun. Each of these pollutants can be attributed to various industries or causes (more about that below). 

The AQI is useful, but it’s not the whole story. We could be having a bad ozone day because it’s 98 degrees and sunny. The current AQI reports you see are usually drawing on the reading of the highest pollutant at that moment — again, recently in Colorado, that’s ozone. So if you see the AQI at 90 in Jefferson County on a hot afternoon, that likely means monitors are measuring 90 parts per billion of ozone, and that’s not good. 

While Colorado’s Front Range counties have slowly ratcheted down average measured ozone levels in recent years, our violations of EPA rules are actually getting worse. That’s because the EPA has moved even faster to lower the acceptable ceiling of ozone, in accordance with new science about lung and tissue damage.

The EPA has since 2015 said that metro areas should not spike above 70 parts per billion (ppb) of ozone, while Colorado this summer has been hitting 80s and 90s on a regular basis. Credible scientists are pushing the EPA to lower the ceiling even further to 65 ppb, which would of course mean even more violation days in Colorado.

That means the EPA keeps putting us into more serious categories of failure. Those failures eventually have consequences, such as requirements to change the vehicle fuel mix or clamp down harder on emissions from oil and gas producers. But it takes years for the bureaucracy to agree on new limitations and get them implemented, often against the opposition of industry and consumers. 

Q: What are the main health risks on high pollution days, and should I keep my kids indoors above a certain level on the AQI? 

A: The EPA’s ozone-explainer website puts it like this: “Children are at greatest risk from exposure to ozone because their lungs are still developing and they are more likely to be active outdoors when ozone levels are high, which increases their exposure. Children are also more likely than adults to have asthma.”

Ozone and particulates both can irritate and inflame the airways. Inflammation causes swelling and other bodily reactions, and obviously, coughing and scratchy throats. They can irritate everyone, but it’s a common sense rule that they are even harder on people with predisposition to asthma or other chronic respiratory conditions. 

What to do with your kids is a dilemma many urban parents, and many urban school principals, must face nearly every day. A National Jewish study with Denver Public Schools found they could closely correlate bad air days with registered uses of asthma inhalers at school health clinics, where students store their medications. Principals have complained they don’t have strong guidance from their districts, and often make their own calls about go or no-go on outdoor recess and exercise on the worst days. 

ozone air pollution EPA Denver Air Quality Index
The EPA and Colorado Air Quality Index starts issuing warnings when Front Range air gets above 100 on the AQI. Above 150, the AQI is considered unhealthy for just about everyone. (Screen capture, Environmental Protection Agency Air Now)

The AQI numbers can be helpful here, argues the state’s Scott Landes. When the AQI is about 100, people who are already sensitive to air pollution risks need to start being more cautious. That includes young children, children with asthma problems, the elderly, and any adults with ongoing respiratory issues. Once the AQI nears 150 or above, the warning starts to cover everyone. People should save their most strenuous exercise or exertion for before noon or after 8 p.m., when ozone levels tend to cool off. 

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That, of course, does not protect people who must work outdoors all day, which leads to some of the tougher economic and environmental questions facing the northern Front Range “non-attainment” areas that are out of compliance with federal pollution limits. 

Q: Do home air filters work, and if so, what should I look for in one? 

Yes, they do work on particulate pollution, but they can also be expensive for many families. A filter with enough fan power to cover a medium-to-large living room can be $200 to $300. Look for online reviews on noise levels, it makes a difference. Most mainstream air filters or purifiers do well on particulate pollution, the tiny woodsmoke, dust and chemical particles called PM2.5 or PM10 depending on their size.

 “I recommend going with the tried-and-true high efficiency particulate air (HEPA) filtration units that can remove at least 99.97% of airborne particles, including dust, pollen, mold, bacteria and viruses,” said Bill Hayes, air quality program coordinator for Boulder County Health. “Units that also utilize activated carbon can have the added benefit of removing some odors and chemicals.”

Make sure the filter you choose has the put-through power to clean the square footage of the room where you’ll be putting it, he noted. 

“I strongly advise against the use of ionizing air purifiers. Few of these devices have been proven effective at reducing airborne pollutants and may produce harmful ozone,” Hayes added. 

The recommended commercial air filters don’t work on ozone, but that’s OK. 

“The one good thing about ozone is that you can escape it by being inside,” Landes said. The chemical disintegrates on contact with most surfaces. 

There are very good answers about how to choose a home air filter starting on page 5 of this online EPA pamphlet

Q: What are the biggest causes of ozone and particulate pollution in Colorado? 

The biggest culprits right now are oil and gas production and refining, driving petroleum-fueled vehicles, emission from coal-fired power plants, industrial plants and wildfire smoke. 

But hear us out, it’s more complicated than that. 

Some of Colorado’s air pollution is direct. Oil and gas production, for example, causes a large amount of both the nitrogen dioxide pollution here, and the largest share of volatile organic compounds, or VOCs. 

Ground-level ozone is created when nitrogen dioxide mixes with the VOCs, and then that chemical casserole is baked by hot sunshine. That’s why ozone peaks in the afternoon. Lately scientists have learned afternoon ozone doesn’t dissipate as much as they’d assumed, because Colorado’s geography and weather patterns swirl the ozone deep into the foothills and then back onto metro areas at night. 

air pollution ozone microns comparison human hair PM10 PM2.5
A comparison of the relative sizes of the pollution most Coloradans worry about. Note that anything PM2.5 or smaller can’t be seen with by the human eye. (Environmental Protection Agency guide to home air filters)

Colorado industries have pointed to state research showing that up to 5 ppb of ozone growth measured in Colorado is the result of pollution drifting east from Chinese coal-fired power plants and California smog

“The Denver metro and northern Front Range area typically sees background levels of ozone between 40 and 50 parts per billion,” Hayes said. “The vast majority of this background ozone is from neighboring states (including California) . . . Only a very small amount is carried from offshore (China, etc.) The national standard for ozone is currently 70 ppb, so a significant amount of our ozone pollution is within our control.”

As Hayes indicates, Colorado is now regularly violating the ozone limits by far more than that amount, and Gov. Jared Polis has directed his administration to not claim outside pollution as a reason to seek exemptions from EPA sanctions. 

So in the areas that state and local regulators could theoretically control, cleaning up oil and gas production and cutting miles driven by petroleum-powered vehicles hold the most hope for meaningful pollution cuts. The state has imposed tighter regulations requiring leak-proof oil and gas equipment; conservationists want more. 

Cutting miles driven is politically volatile — large employers objected strenuously to proposed rules this summer requiring cuts to the miles driven by commuting workers, and the state quickly backed off to make the program voluntary. 

Moving a majority of the Front Range driving fleet to electric power could make large pollution cuts, provided the electricity is generated cleanly by wind and solar plants. State leaders are pushing for rapid fleet electrification, but actual sales to the public of electric vehicles are about 6% of the total market

Gas-fueled vehicles are one of the primary sources of pollution on the Front Range and in the foothills that help cause ozone and greenhouse gases. (Olivia Sun, The Colorado Sun)

Other industries also contribute greatly to the portion of ozone created by VOCs. Readers asked us, if it smells bad, is it pollution? The answer is usually “yes.” 

Suncor’s refinery is a prime example — emissions from cracking open oil into gasoline and other compounds creates a huge amount of VOCs and greenhouse gases. Other “smell” industries contribute, from paint makers to parts manufacturers to electroplating. Consumer products like hair spray, shampoos and more also add greatly to the VOC problem. 

Q: Is there evidence of long-term damage from exercising at high ozone or particulate periods? Put another way, “If I run 10k on a polluted evening, am I in better health or worse health than when I started?” 

The most immediate danger is for those already experiencing asthma or other respiratory and heart conditions, experts say. But with ozone levels spiking above 90 parts per billion, and even above 100 on some recent days, everyone should be aware of the conditions and adjust their habits. 

Remember that ozone and particulate pollution are irritants that cause lung tissue and respiratory areas to become inflamed. 

“Going for a single run during a period of high ozone pollution may not cause long-term health impacts for a healthy individual, but repeated exertion on high ozone days can cause permanent lung damage resulting in decreased respiratory capacity,” Hayes said. “Prolonged ozone exposure can also impact other organs and functions.”

National Jewish Health professor and researcher Jim Crooks said evidence shows healthy adults benefiting overall even when exercising in relatively polluted areas. He notes that the American Heart Association released a statement in 2020 saying “the beneficial effects of increased activity easily offset the combined potential mortality risk of increased air pollution exposure and traffic accidents, in all but the most polluted cities in the world.” 

None of the most polluted cities in the world are in the U.S., he added. 

Crooks goes on to add some caveats. Only a few studies have tried to pinpoint “exactly where that trade-off occurs,” he said. The answer, of course, depends — on the overall health of the athlete, how bad the pollution is during those hours of exercise, the intensity of the workout, etc. And those studies focus on healthy adults, he adds, rather than on children or adults with chronic disease. 

In other words, if you have any conditions at all or are worried about your kids, talk to a doctor. 

Q: Can facemasks help outdoors when air pollution is high? Does it help with ozone? 

Yes, masks can help, if it’s a quality mask, and if you’re talking about particulate pollution. No, if you’re talking about ozone or an ill-fitting cloth mask left over from your pandemic avoidance. 

“While they have been shown to be highly effective at significantly reducing the spread of the coronavirus, the face coverings that we’ve all become accustomed to wearing during the pandemic do little to protect us from most air pollutants,” said Boulder’s Bill Hayes. “They do not provide a barrier to gases such as ozone (and oxygen for that matter) and are not up to the task of filtering fine PM 2.5 particles.”

Colorado’s Landes put it bluntly: N95 masks will filter out wildfire smoke particulates. Our cloth masks for COVID-19 do not.The mask fit also makes a difference, Crooks said. “Wearing a tight-fitting mask that filters out certain air pollutants may be beneficial as well, though the evidence is modest. It should be noted that cloth or surgical masks typically used to prevent COVID-19 transmission may not be tight enough around the face or filter our air pollution effectively enough.”

Hayes likes to add one last suggestion: taping a HEPA furnace filter to a window-insert fan on a hot day is just as dumb as it sounds — and yet people have done it, which is why he brings it up. It won’t really work, and the fan will overheat trying to push the air through the tight filter.

Then you’ll have an electrical fire to deal with on top of all the wildfires.

Stay safe, Colorado.


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