How to get pollutant column density via CMAQ5.0

I was going to use CMAQ 5.0 to simulate to get the pollutant column density. However I found a couple of problems while reading the information on the following website ( Firstly, from the code on the URL it looks like we need to get the upper and lower limits of the integral. Is the idea that the upper and lower integral limits are obtained based on the number of layers we define, with the first layer being the lower limit and the 45th layer being the upper limit correct? Secondly, from the code on the web site, we need to get the full altitude layer (m) and the atmospheric density data (kg/m^3), which I don’t see in the meteorological file, is it not generated? Or where should I view them? Or do you know where to get the sample code to get the pollutant column density based on the CMAQ5.0 model simulation? I hope you guys help me, thanks a lot!

Firstly, I would kindly ask why you use such an outdated version of CMAQ…
Secondly, it would be very easy and convenient to use CMAQv5.4 to solve this problem as CMAQ does provide vertical column density for several air pollutants (NO2, SO2, etc.) in CCTM_PHOTDIAG files. The only thing you need to do is to set the PHOTDIAG in the run.cctm.csh file to T if you upgrade the CMAQ version.