Daily PM2.5 AQI
The daily PM2.5 AQI is calculated by taking the 24-hour concentration average from midnight to midnight (Local Standard Time) and converting to AQI using the PM2.5 cutpoints. 75%, or 18/24 hours of data are needed for a valid daily AQI calculation.
Example 1: Valid
Example 2: Insufficient Data for Calculation
Hourly PM2.5 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 PM2.5, click here.