US AQI for PM2.5
Published by the US Environmental Protection Agency (EPA). The official index in the United States, shown on AirNow and by many weather and air apps worldwide; its PM2.5 cut-offs were lowered in February 2024.
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). You see SmogRank's numbers on this scale.
Convert a reading
Set at 6.1 µg/m³, the middle of the 2515 cities on the 24-hour board.
Try 15.0 µg/m³ (the WHO's 24-hour guideline) or 102.6 µg/m³ (eManzimtoti over the last 24 hours).
Its bands
Good
US AQI 0–50 · up to 9.0 µg/m³
The EPA sees little or no risk for anyone.
Under the WHO's 24-hour guideline (15 µg/m³).
Moderate
US AQI 51–100 · over 9.0 to 35.4 µg/m³
Acceptable for most people; people unusually sensitive to particles may feel it.
Takes in the WHO's 24-hour guideline (15 µg/m³).
Unhealthy for sensitive groups
US AQI 101–150 · over 35.4 to 55.4 µg/m³
People with heart or lung disease, older adults and children are more likely to feel effects; most others are not.
Over the WHO's 24-hour guideline (15 µg/m³) all the way.
Unhealthy
US AQI 151–200 · over 55.4 to 125.4 µg/m³
Anyone may start to feel effects, and the sensitive groups more seriously.
Over the WHO's 24-hour guideline (15 µg/m³) all the way.
Very unhealthy
US AQI 201–300 · over 125.4 to 225.4 µg/m³
A health alert: the risk rises for everyone.
Over the WHO's 24-hour guideline (15 µg/m³) all the way.
No measured city in this band on the 24-hour board now.
Hazardous
US AQI 301+ · over 225.4 µg/m³
Emergency conditions: everyone is likely to be affected.
Over the WHO's 24-hour guideline (15 µg/m³) all the way.
No measured city in this band on the 24-hour board now.
The meanings above are ours, in short. The publisher's own advice for each band: the US Environmental Protection Agency (EPA).
Each scale here is its PM2.5 part only. Official indexes take the worst of several pollutants, so a city's official number can be higher. The scales are defined on 24-hour means (AQHI+ on hourly ones); how we use them.
Other scales
India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. Every scale side by side.
Nothing on SmogRank is medical advice. For health guidance during bad air, follow your local health authority.