What is the Air Quality Index?

A scale from 0 to 500 that the US Environmental Protection Agency uses to report how clean or polluted the air is. It runs from Good (0 to 50) through Moderate, Unhealthy for Sensitive Groups, Unhealthy and Very Unhealthy to Hazardous (301 and above). The number reported for a place is the highest index among the pollutants measured there, and the pollutant that produced it is named beside it.

Who counts as a sensitive group?

People with asthma or other lung disease, people with heart disease, children, older adults, and anyone exercising or working hard outdoors. For ozone, people who are unusually sensitive are affected first; for fine particles, people with heart or lung disease are.

Is smoke drawn overhead the same as smoke you breathe?

No. NOAA's Hazard Mapping System analysts draw smoke they can see in satellite imagery, which is often thousands of feet up and has no effect at ground level. The near-surface smoke forecast on each town's page is the one that matters for breathing, and the two often disagree.

Air Quality Today in the United States

Q: Are these numbers measurements or forecasts?

Both, and each page says which is which. An index beside a monitor's name is a measurement, published hourly by AirNow and preliminary until the operating agency certifies it. A category for today or tomorrow is a state or local agency forecaster's own forecast for a reporting area. An hourly index is NOAA's air quality model on a five-kilometer grid, not a reading from any instrument.

Monitors are reporting an index of 113 at Yosemite National Park, CA, which is Unhealthy for Sensitive Groups, from fine particles (PM2.5). Across the 762 reporting areas measuring right now, 122 are above Good and 1 are above Moderate. Agency forecasters expect 128 areas above Good tomorrow. NOAA’s analysts have drawn wildfire smoke over Alabama, Arkansas, California, Connecticut, Delaware, District of Columbia and 30 other states.

Areas reporting: 762
Worst index now: 113
Above Moderate: 1
Alerts in force: 0

Air quality for your town

Every town in the United States has a page here: what the nearest monitor measured, the category its agency forecasts for today and tomorrow, NOAA’s model hour by hour, and smoke overhead. Choose a state below if the search does not load.

Worst air right now 30

The reporting areas with the highest measured index this hour. Each links to the nearest town’s page.

Reporting area	State	Index	Category	Pollutant
Yosemite National Park	CA	113	Unhealthy for Sensitive Groups	PM2.5
Louisville	KY	79	Moderate	PM2.5
Central	NJ	76	Moderate	PM2.5
Coachella Vly	CA	73	Moderate	PM2.5
Tacoma-Puyallup	WA	70	Moderate	PM2.5
Bakersfield	CA	69	Moderate	PM10
Houston-Galveston-Brazoria	TX	67	Moderate	PM2.5
Shreveport	LA	67	Moderate	PM2.5
Decatur	IL	64	Moderate	PM2.5
Joshua Tree National Park	CA	64	Moderate	Ozone
Memphis	TN	64	Moderate	PM2.5
Metro Riverside CO	CA	64	Moderate	PM2.5
Monroe	LA	64	Moderate	PM2.5
Fresno	CA	63	Moderate	PM10
Salem	OR	63	Moderate	PM2.5
Seattle-Bellevue-Kent Valley	WA	63	Moderate	PM2.5
Vancouver	WA	63	Moderate	PM2.5
Evansville	IN	62	Moderate	PM2.5
Sunnyside	WA	62	Moderate	PM2.5
Visalia	CA	62	Moderate	PM10
Clarksville-Montgomery County	TN	61	Moderate	PM2.5
Hanford	CA	61	Moderate	PM10
Little Rock-North Little Rock	AR	61	Moderate	PM2.5
South and West Suburbs (Chicago)	IL	61	Moderate	PM2.5
Cleveland	MS	60	Moderate	PM2.5
Indianapolis	IN	60	Moderate	PM2.5
Charleston	SC	59	Moderate	PM2.5
Hernando	MS	59	Moderate	PM2.5
Owensboro	KY	59	Moderate	PM2.5
Portland	OR	59	Moderate	PM2.5

Tomorrow

State and local agency forecasts for Monday, September 21, worst first. These are forecasters’ categories for the day, not model output.

Reporting area	State	Category	Index	Pollutant
Nashville	TN	Moderate	90	Ozone
Memphis	TN	Moderate	80	Ozone
Brawley	CA	Moderate	74	Ozone
Calexico	CA	Moderate	74	Ozone
El Centro	CA	Moderate	74	Ozone
Imperial Valley	CA	Moderate	74	Ozone
Niland	CA	Moderate	74	Ozone
Westmorland	CA	Moderate	74	Ozone
Baton Rouge Area	LA	Moderate	67	Ozone
Shreveport	LA	Moderate	67	Ozone
Monroe	LA	Moderate	62	PM2.5
Auburn	CA	Moderate	61	Ozone
Colfax	CA	Moderate	61	Ozone
Dayton	OH	Moderate	61	Ozone
Lincoln	CA	Moderate	61	Ozone
New Orleans	LA	Moderate	61	Ozone
Roseville-Rocklin	CA	Moderate	61	Ozone
Alexandria	LA	Moderate	58	PM2.5
Birmingham	AL	Moderate	58	Ozone
Forsyth County-Winston-Salem-Greensboro-High Point	NC	Moderate	57	PM2.5
Oakland	CA	Moderate	55	PM2.5
San Francisco	CA	Moderate	55	PM2.5
Yuba City and Marysville	CA	Moderate	55	Ozone
Cool	CA	Moderate	54	Ozone
Lake Charles	LA	Moderate	54	Ozone
Phoenix	AZ	Moderate	54	Ozone
Placerville	CA	Moderate	54	Ozone
Anson County	NC	Moderate	53	PM2.5
Buncombe County	NC	Moderate	53	PM2.5
Cabarrus County	NC	Moderate	53	PM2.5

What is driving it

PM2.5 is the measured driver in 499 areas. Fine particles come from smoke, vehicle exhaust, wood burning and industry, and reach deep into the lungs.
Ozone is the measured driver in 235 areas. Ozone is made by sunlight acting on traffic and industrial exhaust, so it peaks on hot sunny afternoons.
PM10 is the measured driver in 28 areas. Coarse particles come from dust, road grit and construction, and are lifted by wind.
Wildfire smoke has been drawn over 36 states today by NOAA’s Hazard Mapping System analysts: Alabama, Arkansas, California, Connecticut, Delaware, District of Columbia, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Virginia, Washington and West Virginia. Smoke drawn overhead is not always smoke you breathe; each town’s page gives the near-surface forecast.

Air quality alerts

An Air Quality Alert is issued by the National Weather Service on behalf of a state or local agency when pollution is expected to reach a level that harms health. An Air Stagnation Advisory means the air will not move enough to clear what is already in it.

None are in force right now.

Every state

Each state’s reporting areas, the smoke over it and the alerts in force.

What these numbers are. An index beside a monitor’s name is a measurement, published hourly by AirNow and preliminary until the operating agency certifies it. A category for today or tomorrow is a state or local agency forecaster’s own forecast for a reporting area. An hourly index is NOAA’s air quality model on a five-kilometer grid, not a reading from any instrument. Where a town has no monitor within reach, only the model figures appear, and the page says so.

Observations and daily forecasts from AirNow, the US Environmental Protection Agency’s program with NOAA, the National Park Service, NASA, tribal, state and local agencies. Hourly forecasts from NOAA’s National Air Quality Forecast Capability. Smoke analysis from NOAA’s Hazard Mapping System. Alerts from the National Weather Service. Index categories and breakpoints are EPA’s, as revised in 2024.

What is here

Measured now: The latest hour from every AirNow monitoring site and reporting area in the country, with the pollutant that produced the index and the agency that reports it.
Today and tomorrow: Each state or local agency's own forecast category for its reporting areas, written by a forecaster, with the discussion they filed alongside it.
Hour by hour: NOAA's National Air Quality Forecast Capability at a town's own coordinate: fine particles and ozone for two to three days, turned into the index by EPA's own method.
Smoke: Where NOAA's analysts have drawn wildfire smoke in today's satellite imagery, and what the model expects near the ground, which is the part you breathe.

Common questions

Why does my town have no monitor?

There are a few thousand regulatory monitors in a country of a hundred thousand populated places, so most towns are nearer to a monitor in another town than to one of their own. Each page names the instrument its reading came from and how far away it is, so you can judge how much the reading is worth where you are. The hourly model forecast covers every point whether a monitor is nearby or not.

Why is the index higher than the concentration suggests?

The index is not the concentration. Each pollutant has its own table of breakpoints, and ozone is scored on an 8-hour average while fine particles are scored on a 24-hour average. An hourly particle reading is turned into an index by EPA's NowCast, which weights the recent hours more heavily when the concentration is changing fast.

Is pollen here?

No. No public agency publishes a pollen forecast for the United States, and the commercial feeds are paid. Where a free and public source appears, it will be added here.

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