Anthony Gerber had every intention of going for a vigorous bike ride last Sunday, until he walked outside his home in Denver’s Central Park neighborhood and caught a whiff of West Coast wildfire smoke.

“It smelled like I was next to a barbecue,” Gerber said. “I thought, that kind of intense aerobic activity, breathing stuff really deep into your lungs? Maybe not.”

Not a good idea, that is.

Gerber is an expert on the dangers of unhealthy air. He is the director of Pulmonary Research at National Jewish Health, as well as a University of Colorado medical professor and chair of the Colorado Air Quality Control Commission.

While Sunday’s air quality convinced Gerber to nix his bike ride, making decisions on whether to exercise in the poor air conditions that have prevailed recently along the Front Range isn’t always so clear cut. The Colorado Department of Public Health and Environment, which issues air quality alerts when conditions are problematic, lists six levels of air quality from good to hazardous. Air that is rated “unhealthy for sensitive groups” may not be cause for concern for those without compromised cardio-pulmonary systems.

“It’s a pretty complicated decision,” Gerber said. “If you’re having symptoms, if you have asthma or some other kind of heart or lung disease and you begin to notice, ‘I feel a lot worse today when I’m out hiking,’ I wouldn’t do that again. I would probably say maybe that activity, when the air pollution is bad, is not the thing for you to do.

“If, on the other hand, you go for a hike and you notice the smell but you’re not really noticing that it’s changing your performance, we think there is a very small risk in otherwise healthy people.”

One comprehensive source for making informed decisions is the Colorado Air Quality Summary maintained by CDPHE, which offers a rundown of air quality forecasts, public health recommendations and links to other important sources of information. CDPHE issues “action day” advisories when the air is bad — or is forecast to become bad — and those alerts are explained in the air quality summaries.

It’s also important to note that conditions can worsen as the day progresses with rising ozone levels that tend to diminish overnight, and that there may be a range of air quality ratings across the Front Range at any given time. Another handy CDPHE resource is its Monitoring Sites Map Air Quality Index, which shows hourly air-quality readings at sites across the Front Range and around the state. A pocket of air that is rated unhealthy for sensitive groups may be surrounded by sites where the AQI is rated good or moderate.

Monitoring sites on the map are color-coded, corresponding to the air quality rating system: Green is good, yellow is moderate and orange is “unhealthy for sensitive groups.” Red, purple and maroon stand for unhealthy, very unhealthy and hazardous, respectively. Among the metrics that determine air quality are two that have been a big problem lately: particulate matter (from wildfire smoke) and ozone.

So how should you decide whether to exercise outdoors when the air is hazy? There are several considerations to keep in mind. For example, Gerber notes that going for a hike in the mountains may help you get around the ozone problem.

“There’s much less ozone as we move out of the urban area and out of that inflection point with the foothills, where some of the more volatile organic compounds that promote ozone get trapped,” Gerber said. “Not that there’s no ozone, but you’re unlikely to have the levels that we have closer to the urban area.

“The second issue is related. Some of the smoke that we’re getting does not necessarily equally distribute across the Colorado Rockies, so you can find areas to hike where the particulate level might be better, depending on how far you’re willing to drive. We know the Front Range kind of traps some of the particulates, and we’ve also got the urban-generated particulates that we always have. So you might be able to find some areas where that AQI is actually better when you’re hiking.”

Air quality issues and poor visibility don’t appear to be discouraging people from visiting Rocky Mountain National Park.

“Our 5 p.m. ‘night before’ (reservation) releases are still filling up and we are not seeing cancellations,” said the park’s public affairs officer, Kyle Patterson. “Some people might be choosing not to come and not canceling, though. We should know more at the end of the month when we look at the overall data. Because smoke and poor air quality is impacting so many states, it may be that people are continuing with their travel plans.”

Gerber won’t exercise outdoors when the AQI is purple or maroon (very unhealthy or hazardous) but he will head out when it is yellow or orange (moderate or unhealthy for sensitive groups).

What would he advise if someone did have a reservation for Rocky Mountain National Park, with plans to go hiking, and air quality was rated moderate? For those who are healthy and not having symptoms related to air pollution exposure, Gerber said experts believe it’s probably OK to hike in moderate wildfire smoke, although he might advise doing a less strenuous hike than what a group had been planning.

“I don’t want to make it a binary choice,” Gerber said. “I think it’s really a risk-management choice. Every person has to metric that differently. For some people, exercise is just so crucial for their mental health and psychological well-being. For that person, it might be a different calculation from someone who says, ‘I’m not going outside and hike in Rocky Mountain National Park, I’ll get on my treadmill in the basement.’ This is really different from the recommendation to wear a mask for COVID, where you are protecting other people. Here it is truly a personal decision. The risk is your own.”

Gerber is concerned about the cumulative effects of breathing problematic air over time, though, noting that he can’t remember the last time Colorado didn’t have “a smoke-filled summer.” Last year, Colorado had to deal with smoke from several wildfires in the state including the Grizzly Creek, Cameron Peak and East Troublesome fires. Much of the smoke now is coming from the West Coast, especially the Dixie fire in northern California, the second-largest in that state’s history.

“You start to feel that if every year for two months you’re out vigorously exerting in high-particulate pollution, most people are going to be fine, but the risk that you might start to hurt your lung function over time with those repeated exposures does go up,” Gerber said. “With as bad as things have been for so long, I’d probably encourage people to think, if they bike every day, in the heat of the wildfire season maybe that’s four days a week.”

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