# Forecasting Ozone and PM concentrations from AQI values

**URL:** https://forum.airnowtech.org/t/forecasting-ozone-and-pm-concentrations-from-aqi-values/439
**Category:** Air Quality and AQI Info
**Created:** [April 11, 2023, 7:54pm UTC](https://forum.airnowtech.org/t/forecasting-ozone-and-pm-concentrations-from-aqi-values/439 "2023-04-11T19:54:50Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![rvr5005](https://forum.airnowtech.org/letter_avatar_proxy/v4/letter/r/94ad74/32.png) [@rvr5005](https://forum.airnowtech.org/u/rvr5005)
#### Post date: [April 11, 2023, 7:54pm UTC](https://forum.airnowtech.org/t/forecasting-ozone-and-pm-concentrations-from-aqi-values/439/1 "2023-04-11T19:54:50Z")

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I use an in-house AQ model using regression statistics (that I did not develop myself) and need to better understand the formulas used. If anyone has any input on the formula pasted below I would greatly appreciate it. The formula is being used to calculate AQ concentrations based on AQI values and I need to know what the numbers in bold are used for.

=ROUND(IF(B9\<51,B9/ **0.92593** ,IF(B9\<101,55+(B9-51)/ **3.26667** ,IF(B9\<151,71+(B9-101)/3.5,IF(B9\<201,86+(B9-151)/ **2.5789** ,106+(B9-201)/ **1.0532** )))),0)

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### Author: ![atutterow](https://forum.airnowtech.org/letter_avatar_proxy/v4/letter/a/cab0a1/32.png) [@atutterow](https://forum.airnowtech.org/u/atutterow)
#### Post date: [April 18, 2023, 1:26pm UTC](https://forum.airnowtech.org/t/forecasting-ozone-and-pm-concentrations-from-aqi-values/439/2 "2023-04-18T13:26:46Z")

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Hi Richard,

It looks like the formula is estimating the 8-hr average ozone concentration from AQI. The bolded values represent the difference between AQI in the category divided by the difference in concentration (ppb) within the category, as shown in the first part of the AQI equation here: [The AQI Equation](https://forum.airnowtech.org/t/the-aqi-equation/169).