# Daily and Hourly AQI - PM2.5

**URL:** https://forum.airnowtech.org/t/daily-and-hourly-aqi-pm2-5/171
**Category:** PM2.5
**Created:** [July 5, 2016, 10:56pm UTC](https://forum.airnowtech.org/t/daily-and-hourly-aqi-pm2-5/171 "2016-07-05T22:56:37Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![mwhylton](https://forum.airnowtech.org/user_avatar/forum.airnowtech.org/mwhylton/32/21_2.png) [@mwhylton](https://forum.airnowtech.org/u/mwhylton)
#### Post date: [July 5, 2016, 10:56pm UTC](https://forum.airnowtech.org/t/daily-and-hourly-aqi-pm2-5/171/1 "2016-07-05T22:56:37Z")

</div>

## 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

 ![pmdaily1](https://forum.airnowtech.org/uploads/default/original/1X/6a313d2ffe4e0a2b2045bb3036b85b3975344230.png)

Example 2: Insufficient Data for Calculation

![](https://forum.airnowtech.org/uploads/default/original/1X/c42a2af405b36c84b294b8245ad495795c64ff3c.PNG)

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## 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](https://forum.airnowtech.org/t/the-nowcast-for-ozone-pm2-5-and-pm10/172).