Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Choosing a purifier →Smoke or smog: what causes bad air where you live
Bad-air days come from 2 different pollutants, and they call for different fixes. Fine particles, mostly from smoke, can be filtered out of a room with an air purifier. Ozone, the main part of smog, can't be filtered by most purifiers, so you plan around it. Each county below is colored by both.
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Brown is smoke and particles, blue is ozone, and dark purple-gray is a lot of both. Low: under 1 day a year. Some: 1 to 5. High: 5 or more. Averages for 2018 to 2022. Tap a county or search for it to see its numbers.
Who lives where
| Kind of place | People | Counties |
|---|---|---|
| Smog country Ozone high, smoke low | 37 million | 75 |
| Smog, plus some smoke Ozone high, smoke some | 29 million | 27 |
| Smoke and smog Ozone high, smoke high | 27 million | 32 |
| Some summer smog Ozone some, smoke low | 78 million | 440 |
| A little of both Ozone some, smoke some | 13 million | 60 |
| Smoke, plus some smog Ozone some, smoke high | 12 million | 32 |
| Clean most of the year Ozone low, smoke low | 111 million | 2,105 |
| Some smoke Ozone low, smoke some | 15 million | 276 |
| Smoke country Ozone low, smoke high | 7.3 million | 61 |
What helps
Smoke can be filtered out of a room. Ozone mostly can't, so you plan around it.
Smoke: upgrade the furnace filter
Use MERV 13 if your system can take it, and run the fan.
Furnace filters →Smoke: wear an N95 outside
A well-fitted N95 helps. Cloth and surgical masks do little.
Wildfire smoke guide →Ozone: check the forecast
AirNow posts ozone forecasts by ZIP code, usually the day before.
Skip ozone generators
The EPA says they don't clean the air, and the ozone irritates the lungs. A box fan filter is a safer cheap option.
Build one →Questions people ask about smoke and smog
What's the difference between smoke and smog?
Smoke is mostly fine particles (PM2.5), tiny bits of soot and ash that get deep into the lungs. Smog is mostly ozone, a gas that forms when pollution from vehicles and industry reacts in sunlight. Both can push the AQI over 100, and on some summer days you get both.
Does an air purifier help with ozone?
Most don't. HEPA purifiers catch particles, and a carbon filter removes only some gases. For ozone, the EPA's advice is to limit hard outdoor activity when levels are high, especially in the afternoon.
How many Americans live with frequent smog or smoke?
From 2018 to 2022, about 93 million people lived in counties averaging 5 or more high-ozone days a year, and about 46 million in counties averaging 5 or more smoky days (fine particles over 35.4 µg/m³). About 111 million lived in counties with under 1 of each.
Why does my county have smoke in winter?
In valleys and northern towns, cold, still air can trap smoke from wood stoves and other burning near the ground for days. That shows up as smoky days from November to February.
These maps use the CDC Environmental Public Health Tracking Network's daily estimates of fine particles (PM2.5) and ozone for every county in the lower 48, 2001 to 2022. A bad-air day is a day when the worst spot in a county goes over 35.4 µg/m³ of fine particles or 70 ppb of ozone, where the AQI passes 100. How we count · Download the data