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Interpret the AQI Rating

Information about interpreting the EPA's Air Quality Index rating and scale.

Each National Ambient Air Quality Standards (NAAQS) pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration where health effects for each pollutant begin to affect the general public. AQI ratings below 100 indicate no appreciable health risk.

Additional information about the AQI and how it can be used is available from the EPA.Exit to EPA

The AQI scale is divided into the following categories:

AQI Air Quality Scale

The AQI for ozone is based on the either the peak eight-hour running average since midnight OR the peak one-hour measurement since midnight. The AQI's for sulfur dioxide, PM-10, and PM-2.5 are based on a 24-hour average sampled from midnight to midnight, and the AQI for carbon monoxide is based on the peak eight-hour running average since midnight. On most days the critical pollutant is ozone. Ozone one-hour average concentrations of 125 ppb or higher exceed the old NAAQS (AQI rating of 106 or higher). The new NAAQS for ozone is based on eight-hour averages and applies in all areas that are classified as attainment for the old one-hour NAAQS. An eight-hour average of 76 ppb exceeds the new NAAQS for ozone. All areas currently classified as nonattainment for the old one-hour standard will still be required to achieve attainment of the one-hour standard (Houston-Galveston-Brazoria, Dallas-Fort Worth, El Paso, and Beaumont-Port Arthur).