Austin Air Quality Index

Quick answer: the Air Quality Index (AQI) is the EPA's 0 to 500 scale for outdoor air. Lower is better. The overall number is the highest score among ozone, fine particles (PM2.5), coarse particles (PM10), nitrogen dioxide, carbon monoxide and sulfur dioxide, so the pollutant with the top score sets the day's AQI.

What drives Austin's numbers

Ozone. On hot, sunny, still afternoons, sunlight turns vehicle and industrial exhaust into ground-level ozone. Central Texas ozone season runs roughly March through November, and the Texas Commission on Environmental Quality (TCEQ) calls Ozone Action Days when high levels are expected.

Pollen. Austin has pollen in the air nearly all year: Mountain Cedar (Ashe juniper) from December to February, oak and elm in early spring, grasses from spring into fall and ragweed from late summer into November. Pollen is not part of the AQI, so the dashboard shows typical monthly levels on their own.

Smoke and dust. In spring, south winds can carry smoke from agricultural burning in Mexico and Central America. In summer, Saharan dust crosses the Atlantic and can turn the sky milky. Both raise particle readings (PM2.5 and PM10).

On poor air days

When the AQI is above 100, or smoke or dust is in the forecast, consider keeping windows and doors closed until conditions improve. On good days (AQI 50 or below, with low pollen) it's a nice time to open up the house.

Where the numbers come from

The AQI, forecast and weather come from Open-Meteo's forecast models (CAMS) and are shown in Austin time. They are modeled values, not monitor readings, and can differ from official monitors. For official monitor readings, see AirNow.gov. Pollen levels are typical Austin levels for the month, not today's counts.