Keep one room clean
On smoky days, shut the windows and run an air purifier sized for that room.
Choosing a purifier →
From EPA monitors and CDC estimates
Know the air where you live
How many bad-air days your county gets, which months bring them, and what to do about it.
AugustAverage bad-air days by county, CDC estimates for 2001 to 2022
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247 million
people live where August averages at least 1 bad-air day
69% fewer
ozone days for the average American than in the early 2000s
311 counties
have more bad-air days than in the early 2000s, mostly in the West
Explore the data
22 years of daily estimates for every county in the lower 48, from a month-by-month map to a finder for families with asthma.
The air quality map
Play through the year and watch ozone and smoke move county by county.
Open the map →Is the air getting better?
Every county from 2001 to 2022, and what changed since the early 2000s.
See the trend →Smoke or smog?
Find out whether your bad days are particles or ozone, and what fixes each.
Check my county →Where to live with asthma
Set the bad-air days you can live with and see which counties fit.
Find counties →Compare counties
Put 2 or 3 places side by side, month by month and year by year.
Compare →Browse by state
Every state's counties with EPA monitors, ranked by bad-air days.
Pick a state →Where the air is worst and best
Counties of 250,000 people or more. Bad-air days a year from EPA monitors, 2021 to 2025. Full list of the worst · Full list of the cleanest
Most bad-air days
Mostly ozone, in California's valleys and around Phoenix
Cleanest air
Counties that measure both ozone and particles year-round, fewest bad days
What the AQI colors mean
The Air Quality Index runs from 0 to 500. We count a bad-air day as any day over 100, when the EPA says children, older adults and people with asthma or heart disease should cut back outdoors. How the AQI works
Good0 to 50
Air pollution poses little or no risk.
Moderate51 to 100
Fine for most. Unusually sensitive people may want to take it easier.
Sensitive groups101 to 150
Kids, older adults and people with asthma should cut back.
Unhealthy151 to 200
Everyone should ease off hard outdoor exercise.
Very unhealthy201 to 300
Health alert for everyone. Stay in a clean room if you can.
Hazardous301 to 500
Health warning of emergency conditions. Everyone should avoid all outdoor activity.
What helps on bad-air days
Simple steps from EPA advice. Which ones matter most depends on whether your county's bad air is smoke or ozone.
Move workouts to the morning
Ozone peaks on hot, sunny afternoons. Mornings are usually cleaner.
Ozone guide →Upgrade the furnace filter
A MERV 13 filter catches far more smoke than the thin filters many homes use.
Furnace filters →Guides
Plain answers, checked against the EPA, the CDC and California's air board.
What the Air Quality Index numbers and colors meanFrom green to maroon, and who should take care
How to protect yourself from wildfire smokeProtect yourself at home and outside
How to choose an air purifier for smokeSize it by the smoke CADR
How to use your furnace or AC filter against smokeWhy the EPA points to MERV 13
How to make a box fan air filter for wildfire smokeA box fan and a furnace filter
What ozone pollution is and how to avoid itWhy afternoons are worst
Kids, school and bad air: what each AQI level meansRecess, sports and asthma at each AQI level
Pick your state
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