You can’t control the air outside. You can control what reaches your lungs. Here’s what actually works — and what doesn’t.
When air quality is bad outside
1. Run a HEPA filter indoors — and leave it on
A HEPA filter removes fine particles from the air in the room it’s running in. The key word is room — it cleans the air it circulates through, not the whole house. Put it in the room you spend the most time in, run it continuously on bad air days, and don’t cycle it on and off. It needs time to work through a room’s full air volume.
Important: HEPA filters do not remove ozone. If the AQI on the home page is being driven by ozone (it will say so underneath the number), a HEPA filter won’t help. Close windows, limit exertion, and move activities indoors.
2. Close the windows — and storm windows too
Including storm windows if you have them — they add a second barrier that meaningfully reduces particle infiltration. At night when the cool lake air is tempting is exactly when people leave them open. On a bad air day the outdoor air is the problem — bringing it in defeats everything else you’re doing. Close and latch everything.
3. Hit recirculate in the car
Look for the button with a car outline and an arrow looping inside it. That’s recirculate — it cycles cabin air instead of pulling from outside. Your cabin filter, even a good one, can’t keep up when it’s continuously fighting outdoor smoke or ozone. Recirculate cuts the load dramatically. Switch back to fresh air once you’re out of the bad-air area, or periodically on long drives.
4. Wear an N95 outdoors
Cloth masks and surgical masks do not stop fine particles. The filtration isn’t there, and they don’t seal against your face. The mask has to filter and it has to seal — that’s what N95 means.
Where to get one: Walmart carries them in the home improvement section, usually near the paint supplies. Look for a two-pack around $8. The ones with a round valve on the front are worth choosing — the valve vents heat on exhale, making the mask easier to wear for longer. (Protection is identical either way; the valve is comfort, not chemistry.) Check that “N95” is printed on the mask itself — the same shelf carries plain dust masks that filter construction debris but not smoke particles.
People with beards: the seal breaks along facial hair, which means N95-level filtration isn’t happening regardless of what the package says. A powered air-purifying respirator (PAPR) is the alternative, but those are industrial equipment. The practical answer is to shave or stay indoors on genuinely bad days.
5. Check your central air filter — use MERV 12 or higher if your system supports it
Standard filters (MERV 1–8) don’t catch fine particles. A MERV 12+ filter traps PM2.5-sized particles through your whole home’s airflow. Check your furnace manual or the filter slot label for the maximum MERV rating your system supports — too high a rating restricts airflow and can strain the blower.
6. Check on the people who feel it first
Asthma, COPD, heart disease, older adults, young children, pregnant women — these groups aren’t just “more sensitive.” They face measurably higher risk of hospitalization and worse outcomes from the same air quality that healthy adults tolerate. A bad air day is a reason to change plans, not tough it out.
Smoke vs. ozone — different problems, different responses
| Action | Smoke (PM2.5) | Ozone |
|---|---|---|
| HEPA filter | ✅ Helps | ❌ Does not remove ozone |
| Close windows + storm windows | ✅ Helps | ✅ Helps |
| Car recirculate | ✅ Helps | ✅ Helps |
| N95 mask | ✅ Helps | ❌ Does not block ozone gas |
| MERV 12+ furnace filter | ✅ Helps | ❌ Does not remove ozone |
| Exercise outdoors | ❌ Avoid | ❌ Avoid, especially afternoon |
The home page shows which pollutant is driving the AQI. Check it before deciding what to do.
Checking conditions before you go out
The home page gives you the live official AQI and the PurpleAir sensor map. For planning a day ahead, the smoke forecast page shows the NOAA HRRR-Smoke model — the same one professional forecasters use — running out 48 hours.
- Check before outdoor exercise, not after. By the time you feel it, you’ve already been breathing it for a while.
- Wildfire smoke events build slowly and clear slowly. A single reading doesn’t tell you the trend. On suspicious days, check in the morning, midday, and before outdoor plans.
- When PurpleAir and AirNow disagree sharply, conditions are changing fast. Trust PurpleAir for right now, AirNow for the official assessment.
Nothing here is medical advice. If you have asthma, COPD, heart disease, or any respiratory condition, talk to your doctor about your personal action plan for poor air quality days.