Colorado Wildfire Smoke, Air Quality, and Training: Ultimate Guide for Runners and Athletes

September 9, 2025

Blog prepared by AJ Cohen

Episode 33 of Making Strides sparked this deep dive. Huge thanks to our guest, sports science researcher Ty Mangum, whose work looks at environmental health and exercise physiology. This guide translates that conversation into a straight-shooting resource you can use year after year.

In the fall of 2020, when the Cameron Peak fire raged west of Fort Collins, running outside felt like rolling the dice every single day. Some mornings, I’d look out over Horsetooth, and the sky was this eerie mix of red and orange, with ash literally falling in the streets.

AQI readings shot up into the multiple hundreds, making simple decisions like “should I go for a run on the Poudre Trail” feel like a real health gamble.

One of the worst days, I remember strapping my son into the car and driving twenty minutes south to Devil’s Backbone. Down there the air was crisp and clean, AQI in the single digits.

But when we turned north, we could see a massive smoke plume choking Fort Collins, stretching over the city like a wall. It was surreal to be hiking under blue skies while knowing friends training back home couldn’t safely step outside.

Other days were less obvious. On the morning of the Long View Half Marathon, the AQI sat just under 100 before the gun went off, so I decided to race. By the time I crossed the finish line, the number had climbed into the 150s. That day drove home how quickly conditions could flip during wildfire season.

As runners we’re stubborn, we want to get in our miles whether it’s on the Spring Creek Trail or training for the Colorado Marathon, but the truth is, there’s no playbook for when smoke rolls in.

That gap is exactly why I put this resource together. Whether you’re running in Fort Collins, Boulder, Denver, or anywhere else in the country, smoke from wildfires in Colorado, the Pacific Northwest, or even Canada can change the air quality in a matter of hours.

This guide is the one I wish I had back then: simple, practical, and built for athletes who need real answers about air quality index, PM2.5, when to take it indoors, and more!

Image Caption: Large smoke plume from the Cameron Peak Fire (2020) as seen from Devils Backbone, Loveland, CO – photo by AJ Cohen

What’s Actually In The Air

We talk about “air quality” like it is one number. It is not. Air is mostly nitrogen and oxygen. Floating in there are all kinds of extras: dust, pollen, ocean spray, soot, and yes, wildfire smoke. Those floating bits are called particulate matter.

The size that matters most for health and performance is PM2.5. That means particles that are 2.5 microns or smaller. You cannot see them. They are about one-thirtieth the width of a human hair. They are also small enough to slip past your lungs’ normal filters and reach the alveoli, then cross into your bloodstream.

That’s why this topic is bigger than “my lungs feel fine.” PM2.5 affects the whole system.

Another player is ozone. Ozone is useful in the upper atmosphere because it blocks UV. Down at ground level it is an irritant. Ozone tends to be more of a factor at altitude and on hot, sunny days.

For most athletes during wildfire season, PM2.5 is the number to check first. Ozone still matters, but PM2.5 is the workhorse indicator.

AQI, PM2.5, and Why Apps Don’t Always Match

AQI stands for Air Quality Index. Think of it as a score that translates pollutant concentration into a simple range.

Different apps may display different defaults.

One might show PM2.5 AQI.
Another might be showing ozone.
Some pull from government monitors.
Others pull from community sensors that can vary block to block.

Air is local. Wind, inversions, and terrain make big differences across short distances.

The general AQI ranges most people use:

0–50: Good
51–100: Moderate. Use caution if you have asthma or cardiovascular issues
101–150: Unhealthy for sensitive groups. Most athletes should modify
151+: Unhealthy for everyone. Strong case for taking it indoors

You can use any reliable source.

AirNow.gov is a good starting point because it aggregates official monitors, providing clean PM2.5 and ozone views, as well as hourly forecasts.
PurpleAir is also useful because it fills in gaps with lots of local sensors. I like to cross-check the two when I need a fast read on my neighborhood.

Bottom line: make sure you know which pollutant your app is showing. If you only check one number before training, check PM2.5.

What PM2.5 Does Inside Your Body

Quick physiology in plain English. Your lungs have two main jobs:

Gas exchange. Bring oxygen in and move carbon dioxide out.
Filter and defend. Catch junk and help your immune system deal with it.

PM2.5 is small enough to bypass that second job. It gets deep into the alveoli, crosses into the blood, and can trigger systemic effects like inflammation and oxidative stress.

In the short term, this can show up as increased arterial stiffness and changes in how your blood vessels function. Over longer stretches and repeated exposure, risks stack up.

You won’t necessarily feel this during the workout. That is part of the problem. This is not just a “my lungs burn” thing.

Now layer in exercise. When you train, you breathe more air per minute. A lot more. Intensity and duration both drive total exposure.

A hard hour will pull a large volume of air.
A long easy three hours will pull a large volume of air.

Different routes, same concept. The more air you move, the more particles you take in.

If you want help tailoring cutoffs to your health history and race goals, reach out for more info at (970) 500-3427, and we can make a plan that fits your season.

Why Fort Collins and the Front Range Feel It So Often

Living on the Front Range, you sit downwind of multiple wildfire-prone areas. Fires on the Western Slope, in Rio Blanco County, or even as far as British Columbia and the Pacific Northwest can send smoke east in just a day or two.

That’s why you sometimes wake up on a Friday morning with clear skies, only to find smoky skies drifting in by the afternoon.

Current Fires and Regional Air Quality Concerns

Colorado smoke doesn’t just come from new wildfire events in our own state.

Larger areas of the northwestern United States and western Canada frequently contribute. A Stoner Mesa Fire in Dolores County or a blaze in Steamboat Springs can lead to downwind impacts.

The Colorado Department of Public Health and Environment regularly issues air quality health advisories when fine particle pollution reaches sensitive levels.

How Air Quality Monitors Help You Stay Ahead

Air quality monitors around Fort Collins, Loveland, and Colorado Springs give you a real-time sense of particulate matter trends. Pair those with AirNow or PurpleAir, and you’ll have a good feel for what’s moving in.

Keep in mind that local topography can trap outdoor air intake differently in valleys and neighborhoods. Reduced visibility is often a sign that particulate matter is building, but you should rely on the numbers, not just your eyes.

Simple Training Rules You Can Actually Use

There is no perfect line that fits every person in every situation. What you can do is pick clear thresholds in advance and honor them.

Here is a practical starting point.

Before you head out:

Check PM2.5 in your area. Use AirNow.gov or your preferred app.
Glance at the hourly forecast to see if the next few hours trend up or down.
Consider wind direction. A short drive or different trailhead can be night and day.

Cutoffs to consider:

Quality sessions (speed work, tempo, hard long runs): Target AQI under 100.
- If PM2.5 is 50–100 and you are healthy with no respiratory or cardiovascular issues, you might proceed with caution.
- If it is 100+, take the workout indoors or reschedule.
Easy aerobic runs: Prefer 0–100.
- 100–125 becomes a personal risk call. If you go, shorten the duration.
- 125–150: Strong nudge to go inside.
- 150+: Go inside.
Above 150 for anything: choose an indoor option. The juice is not worth the squeeze.

Race week and race day:

Pick a number days ahead as your hard cap and write it down. If the race morning PM2.5 AQI is above that cap, you already made your decision. No bargaining with yourself at the start line.
Monitor the hourly on race morning. Smoke plumes and winds can flip a course from good to nasty within the duration of the race.
Remember there will be other races. Your lungs and cardiovascular system are not single-use items.

Indoors Beats Toughing It Out

When air is poor, moving the session indoors reduces particle exposure because most buildings have some filtration. You can improve it further.

Use a treadmill or bike trainer in a room with the windows closed.
Run an air purifier in that room. You don’t need something fancy. A proven HEPA unit works.
Upgrade HVAC filters during fire season. Even a simple improvement helps.
If budget is tight, a box fan plus a high-quality furnace filter taped to the intake side can lower particulate levels in a small room. Not perfect, still better than nothing.

No, indoor training is not the same as that trail you love. It is a short-term pivot that keeps momentum without rolling the dice on your health.

What About Masks and “Lung Training” Gadgets?

Masks can reduce particulate intake when worn correctly. The catch is, they also add resistance to breathing, trap heat, and complicate fueling. That tradeoff gets bad fast in long or intense sessions. For a casual walk, sure. For a tempo run, it is rough. For an ultra, fueling and hydration become a mess.

If you need to be outside for errands on a smoky day, a well-fitted N95 is useful. For high-intensity exercise, moving the session indoors is usually the smarter play.

On “strengthening your lungs” to tolerate smoke. No. You can strengthen respiratory muscles. You cannot train the alveoli to enjoy toxic particles. Save your effort for training that builds performance, not tolerance to pollutants.

Red Flags That Mean Stop

Most of the physiological changes from PM2.5 are not things you can feel in the moment. A few signs you should take seriously:

Persistent or uncontrollable coughing during the session
Shortness of breath that does not match the effort
Throat or chest irritation that builds as you continue
Wheezing if you have asthma or exercise-induced bronchospasm

If one of these shows up, stop. Get to clean air. You do not get a medal for pressing on through airway irritation caused by smoke.

Recovery After Unexpected Smoke Exposure

Let’s say the forecast looked fine and then a smoke layer drifted in mid-run. You still had to get back to the car. Now what.

Get to cleaner air as soon as you can.
Hydrate and eat normally. Your body will handle the rest.
Antioxidant-rich foods are part of a healthy diet anyway. Fruits and vegetables are great.
Avoid the temptation to drown yourself in unproven supplements. There is no magic pill that reverses particulate exposure.
If you have reactive airways or asthma, follow your plan and check in with your clinician if symptoms flare.

Acute vs Chronic Exposure

One smoky workout is not the end of the world. It can still spike inflammation and vascular stiffness in the short term. The body tends to reverse those changes once exposure drops.

The bigger concern is repeated days at moderate to high AQI. That is when risk stacks up. So if you have a string of smoky days, the cumulative effect matters. Use the indoor plan. Protect the long game.

Practical Adjustments Athletes Can Make

On days with heavy smoke, you’ll notice air quality advisories recommending that sensitive populations and older adults stay indoors.

For athletes, prolonged or heavy exertion outdoors under those conditions raises health impacts even if you feel fine during the workout. A few practical steps help:

Shift key sessions to early mornings when there’s often less smoke.
Close windows and use air conditioning to maintain cleaner indoor air.
Temporarily relocating to an area with less smoke, even just a short drive south or north, can provide a break.
Build an indoor air setup with a purifier so you can keep training momentum without risking lung disease later.

Easy Decision Framework You Can Save

Here is a compact way to run your training day.

Check PM2.5 AQI for your neighborhood.
Look an hour ahead on the forecast.
Decide the session type and match it to a cutoff.
- Quality day needs better air.
- Easy day has more wiggle room, but still has a ceiling.
Pick the environment.
- Clear and under your cutoff: go outside.
- Over your cutoff: go indoors.
- Marginal: shorten and lower intensity or move inside.
Monitor during the run for red flags.
Recover in clean air and move on.

Stick that flow in your notes app. It will save you overthinking on smoky mornings.

Real-World Scenarios

“It smells smoky but the PM2.5 is moderate.”

Smell and AQI do not always track perfectly. Trust the number, not your nose. If PM2.5 is under your cutoff, proceed, and stay alert to symptoms.

“PM2.5 is 95 and I have intervals.”

You can move to a treadmill, cut the reps and keep quality, or swap days so today is easy and quality slides to a cleaner day.

“Easy long run planned and PM2.5 is 110.”

If you go outside, shorten the duration and keep it truly easy. Better option is a split indoor session or a cross-training day on a trainer.

“Race morning starts at 70 and trends toward 140 by late morning.”

Set your cap ahead of time. If your cap is 100, you toe the line if you expect to finish before the spike. If your race is three hours and the forecast crosses your cap at hour two, consider pulling the plug or adjusting expectations with a firm stop point.

Coaching Notes for Athletes

If you coach runners, build this into your system.

Set personal caps in training logs so decisions are automatic.
Create an indoor backup menu for each athlete. Treadmill versions of key workouts. Bike options that hit similar systems.
Educate on red flags so athletes do not try to “tough it out.”
Plan race-week contingencies. If smoke is likely, make the call and communicate it. The more you decide in advance, the less emotion runs the show later.

Frequently Asked Questions

Is one smoky workout actually dangerous?

It can create short-term changes in blood vessel function and inflammation. The bigger problem is repeated exposure. One bout is more reversible. Strings of days are not your friend.

Which is riskier, an hour of hard intervals or a three-hour easy run?

Think total air volume. The long easy run likely wins for total particulate intake. Hard intervals are still not ideal, but shorter duration limits total exposure. Best answer is to avoid both outside when air is poor.

Can I just wear a mask and keep training outside?

For errands, yes. For long or hard workouts, the breathing resistance and fueling issues make it a poor choice. Move the session indoors.

What should I check first, ozone or PM2.5?

PM2.5 is the priority for wildfire smoke. Ozone matters at altitude and on hot sunny days. If you are at elevation, check both.

Why do different apps show different numbers?

Different sensors, different pollutants, and very local conditions. Know what pollutant you are looking at and cross-check when in doubt.

Can I train my lungs to tolerate smoke?

No. You can build fitness. You cannot make alveoli enjoy toxins. Adjust the environment instead.

Resources

AirNow for PM2.5 and ozone with hourly forecasts: airnow.gov
PurpleAir for dense local sensor maps: purpleair.com
Basic HEPA air purifier. Pick a proven unit and run it in your training room during fire season.
Quality HVAC filter. Upgrade during wildfire season and change it on schedule.
N95 respirators for necessary outdoor time when it is smoky.

(If you want a short list of purifier and filter picks, say the word and I’ll add a buyer’s guide. No sponsorships or fluff. Just what works.)

The Three Golden Rules

Choose your caps in advance. Decide your PM2.5 cutoff for quality days and easy days. Write them down. Stick to them.
Check before you train. A quick look at PM2.5 and the hourly forecast saves a lot of grief.
Build an indoor plan. Treadmill, trainer, basic purifier, and better HVAC filters. A simple setup keeps your training rolling when the sky looks like a sepia filter.

Outsmart Colorado Wildfire Smoke to Keep Health Impacts Low

You cannot control where smoke blows. You can control how you respond.

Smart athletes protect both performance and health by making a few clear decisions ahead of time.

Check PM2.5. Respect your caps. Go inside when you need to. You will stack more good training weeks by playing the long game.

If you live in a smoke-prone area, save this post and share it with a training partner. Set your personal caps today and put an indoor backup on your calendar for the next smoky spell.