Daily PM2.5 and PM10 AQI
The daily PM2.5/PM10 AQI is calculated by taking the 24-hour concentration average from midnight to midnight (Local Standard Time) and converting to AQI. 75%, or 18/24 hours of data are needed for a valid daily AQI calculation.
The following examples are for PM2.5. For PM10, follow the same steps. However,
Example 1: Valid
Example 2: Valid with Missing Data
Example 3: Insufficient Data for Calculation
Hourly PM2.5 and PM10 AQI
If viewing/calculating hourly PM2.5 or PM10 AQI for hours >5 old, these calculations are done by using the midpoint 24-hour average concentration converted to AQI. For a given hour, this includes the previous 12 hours, the given hour, and the following 11 hours. 18 of 24 hourly concentrations (75%) are needed for a midpoint 24-hour average.
The following calculations use PM2.5. Follow a similar process for PM10. However, hourly concentrations and averages are truncated to the nearest 1 ug/m3 instead of 0.1 ug/m3.
Example 1: No Missing Data (click image for larger view)
Example 2: Some Missing Data (click image for larger view)