Air Quality Regression Forecasting Model

[StormChaser02]

This is a major shot in the dark but I was hoping there could be someone who could assist.  I am an air quality forecaster that uses an in-house air quality forecast model that uses regression statistics.  The model was developed well before I arrived so when it comes to the inner workings of it, I am still figuring things out.  Anyway, there is a formula (which I will post below) that converts the NOAA AQI into a forecast concentration (ppb) and while I recognize the formula, there are a few numbers (in BOLD) I dont recognize.  I dont know if they are widely used constants or are specific to this mode, in which case this is pointless even post. Any assistance would be greatly appreciated. 

=ROUND(IF(B3<51,B3/0.92593,IF(B3<101,55+(B3-51)/3.26667,IF(B3<151,71+(B3-101)/3.5,IF(B3<201,86+(B3-151)/2.5789,106+(B3-201)/1.0532)))),0)