Daily and Hourly AQI - Ozone

Daily Ozone AQI

The daily ozone AQI is calculated by taking the maximum 8 hour concentration from 07:00-23:00 LST, and then converting to AQI. Each 8-hour average concentration is truncated to .001ppm/1ppb. There are 17 8-hour averages considered in each day. Each 8-hour average requires 6 of 8 hours (75%) for a valid calculation. In addition, 75% or 13/17 of the 8-hour averages are needed for a valid daily ozone AQI calculation.

Example 1: Valid

Example 2: Valid with Missing Data (Red background/text= invalid or missing)

Example 3: Insufficient Data (Red background/text= invalid or missing)

Hourly Ozone AQI

NowCast AQI method

For real-time and other hourly readings, the NowCast method is used to calculate the AQI for each hour. In 2021, the NowCast also replaced the midpoint averaging method (described below) for hourly AQI from older hours. For information on how to calculate the NowCast for Ozone, click here.

Midpoint AQI method (obsolete as of 2021)

Previously, if viewing/calculating hourly ozone AQI for hours >1 old, the hourly AQI calculations would be performed using the midpoint 8-hour average ozone concentration converted to AQI. For a given hour, this included the previous 4 hours, the given hour, and the following 3 hours. 6 of 8 hourly concentrations (75%) were needed for a valid midpoint 8-hour average.

Example 1: No Missing Data

Example 2: Some Missing Data