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)