Poor Air Quality Training Adjustments
- Josh Fields
- Jul 15
- 8 min read
Updated: 6 days ago
Unsurprisingly, much of the United States and Canada are once again facing poor air quality due to wildfires. Don’t be the runner who “toughs it out” only to face unnecessary setbacks—or worse, long-term health consequences. Adjusting your training on bad air days isn’t weakness. It’s smart, sustainable training, and that's what leads to the vast majority of your athletic progress.
This is a seasonal problem, however affected areas vary each year due not only to different wildfires, but also wind and weather patterns.
Prefer to watch a video? You got it! Note that this is a summary video, with a bit less info than the article.
What is AQI?
The Air Quality Index takes a set of pollutant measurements and boils them down to one number that tells you how healthy — or unhealthy — the air is right now. The higher the number, the worse the air. At any given moment it reflects whichever pollutant is worst, which during wildfire smoke is almost always fine particulate matter.
The scale runs across six categories:
0–50 Good
51–100 Moderate
101–150 Unhealthy for Sensitive Groups
151–200 Unhealthy
201–300 Very Unhealthy
301–500 Hazardous
You'll sometimes see readings above 500 during a serious smoke event — apps will happily show you 600 or 700. That's officially "Beyond the AQI," and the guidance is straightforward: treat it as Hazardous or worse, and stay out of it.
Most services also break the number down by component. Usually this includes fine particles (PM2.5), coarse particles (PM10), and ozone. The number in "PM2.5" and "PM10" is the size of the particle, in microns, so PM2.5 means particles 2.5 microns across or smaller.
For scale, a human hair is about 50–70 microns, which makes a PM2.5 particle roughly 25 times thinner.
Coarse particulate matter can be irritating, and include things like dust from a dirt road, farm or mine. This is something we encounter frequently, is often hyper-localized, and settles quickly.
However it's fine particulate matter, PM2.5, that is the most dangerous, as it can penetrate into the deepest parts of your lungs, and even your bloodstream. The most common example is smoke, whether from a woodstove, or from wildfires.
Impacts
As an athlete, it's vital to keep track of the local AQI where you live and train, and adjust your training accordingly. While poor air quality affects everyone, athletes are particularly at risk. A resting human moves roughly 6 liters of air per minute; during a hard effort an athlete can exceed 90 — about 15 times more air, and that much more of whatever's in it. Hard breathing also shifts you toward the mouth, bypassing the nose's filtering and sending particles deeper.
There is research that shows that prolonged exercise in poor air quality can have long-term health implications. High exposure to particulate matter during endurance athletics can lead to increased blood pressure, impaired vascular function and inflammation. Obviously those health implications also affect your training! Above all remember that the concrete number isn't the most meaningful; effects depend on the severity of the particulate matter, frequency and duration of exposure and intensity of breathing.
Remember that one workout, or even one WEEK of workouts just isn't that important compared to your long-term health, fitness and happiness.
Don't derail your progress or threaten your long-term health and performance for a couple of runs.
How Do I Find the Local AQI?
The US EPA (Environmental Protection Agency) operates both an app (iOs or Android) and a website called AirNow. I highly recommend both. It's quick and easy to see your AQI, the component scores, and a map of AQIs near you.
During wildfire season, go straight to AirNow's Fire and Smoke Map. It combines the permanent monitoring stations with temporary and low-cost sensors, so you get a much denser local picture than the official monitors alone — dense enough to answer "is the air better a few towns over?"
That matters, because poor air comes in waves and gets shaped by the terrain. A short drive can sometimes drop you into dramatically cleaner air. Just don't assume lower is better: valleys and low spots tend to trap smoke, especially on calm mornings, so a valley trail can be worse than where you started. Let the map point you toward the clearer air rather than guessing.
AirNow forecasts the next day too. While you can't count on precise numbers, or accuracy on the edges of narrow bands of smoke, you might see that it's ugly today but clearing tomorrow. That might help you with the adjustments below!
Guidelines for Training Adjustments
These are the guidelines I give the athletes I work with. It's important to take them as a starting point, not a rulebook, because there's no single AQI where the air flips from safe to dangerous.
What matters is your dose: how dirty the air is, how hard you're breathing, and how long you're out in it, and how many days you do it. Those first three move together, which is why the same number can mean "go run easy" for one person and "stay in today" for another.
So before you decide, weigh what you're actually working with:
The local AQI where you'll be running.
The PM2.5 reading specifically — for smoke it's usually what's driving the number, and it's the component that matters most for your lungs. A high reading driven by afternoon ozone is a different problem than one driven by wildfire smoke.
How long it's expected to last. One run in bad air is not the same exposure as the fourth straight smoky run.
Any underlying lung condition, or how you're feeling right now. Asthma is a reason for real caution. So is a scratchy throat or tight chest mid-run; that's your body telling you the dose is adding up.
Where you are in your training or racing. Months out, a missed session is nothing. Even close to a goal race, it's rarely worth the trade, but I'll leave that for you to decide.
The run on the schedule. An easy 30 minutes and a threshold workout pull very different amounts of air through your lungs.
Your indoor options: a treadmill, a gym, anywhere you can move a hard session inside.
Nearby pockets of cleaner air, using the map. Sometimes a short drive changes everything.
Here's what I'd recommend for a starting point, but adjust up or down based on the factors above.
Good 0 - 50 — train as planned, no modifications needed
Moderate 51 - 100 — Most easy running is fine. Dial back effort, volume or both on workouts and long runs with intensity in them.
Unhealthy for Sensitive Groups 101 - 150 — Shorter easy runs are okay, but bring workouts and long runs indoors (or switch to short and easy). You can also split long runs so you're only outdoors for part.
Unhealthy 151 - 200 — Short and easy running ONLY, move indoors if you have any option. If it's more than one day, I'd recommend shifting to indoors above 180.
Very Unhealthy 201 - 300 — Indoors, filtered air. No outdoor running.
Hazardous 301 and higher — Absolutely indoor-only. But don't assume inside is automatically safe: if smoke is this heavy, it's seeping into your house too, so you want to be actively filtering and ideally monitoring your indoor air, not just hoping. (More on that below.)
Adjusting Up or Down
The tiers above assume a healthy runner on a normal day. A couple of things shift where you should actually land.
Treat the number as worse than it reads when:
You have asthma, or any lung or heart condition. Drop at least a tier, sometimes more.
You're feeling it right now. A scratchy throat, a tight chest, a cough, a headache: that's a stop sign no matter what the app says. The monitor is averaging air a few miles off; your body is measuring your exact spot and your exact effort.
You're deep in a hard block or carrying heavy weekly volume. You're already fatigued, and more mileage means more air moved. Don't stack a smoke dose on top.
It's the third or fourth straight smoky day. The dose adds up across days, so the same reading calls for more caution late in a stretch than it did on day one.
And just back off without agonizing, when:
You're weeks or months from any goal race. A skipped or shuffled session is worth nothing against your health here. Bag it and move on.
It's an easy day anyway. Moving a recovery run indoors, or just dropping it, has little downside.
It's forecast to clear tomorrow. Trade today's hard session for tomorrow's easy one. You lose very little, and you keep your heavy-breathing day out of the worst air.
A Note on Indoor Air
"Move it indoors" only helps if indoors is truly cleaner. During a heavy smoke event, fine particles work their way into most homes, and an ordinary, unsealed house can end up tracking the outdoor number more closely than you'd think.
The simplest way to know is to measure it: a low-cost indoor air quality monitor will tell you your real number rather than letting you assume. Short of that, assume that the leakier your house and the heavier the smoke, the closer your inside air is to the outside.
Here's how to clean it up, from easiest to most involved:
Seal and recirculate. Close windows and doors. If you have central air, set it to recirculate and turn off any fresh-air intake so you're not pulling smoke in.
Upgrade your furnace filter. A MERV-13 filter captures fine particles across the whole house — as long as your system can handle it without straining airflow. Check the manufacturer's spec first.
Run a HEPA air purifier. A portable unit with a true HEPA filter is the most reliable fix for a single room. Size it to your space (match the coverage rating to your room or go a step larger) and run it on high.
Build a clean room. Pick one room, seal it, and run the purifier there. This is your household's refuge when the air is bad for days.
On a budget: a set of four MERV-13 filters strapped to a box fan is called a Corsi-Rosenthal Box. Use a newer fan with a fused plug so it doesn't overheat, and don't leave it running unattended.
Keep in mind that regardless of your filtration method, it takes time for a filter to move the room's air through it, and it may have trouble keeping up with ingress in a poorly sealed home. Start your filtration as early as you can while numbers are still low.
While the smoke lasts, don't add particles of your own: skip the gas stove, frying, candles, and aerosol sprays, and vacuum only if it's a HEPA vacuum.
One thing specific to us as athletes: filtering a room makes it safe to be in, but a hard run is a different ask. You're moving many times more air, so you'll take in far more of whatever hasn't been filtered out.
Keep indoor efforts easy when the air is marginal, and put the treadmill somewhere you've actually cleaned the air, not in the middle of a smoky house. (And not in the sealed clean room itself, where running would just stir things up.)
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