CAMS Regioal Air Quality Reanalysis total column

Dear all, I am trying to calculate the total column NO2 out of the different altitude levels of NO2 concentrations CAMS Regional AQ Reanalysis dataset. Aim is to compare the total column values of the CAMS Regional to the total columns of the CAMS global and the TROPOMI NO2 columns. Is there a common method to calculate the total column out of the CAMS regional model?

Thanks in advance.