I am working on comparing my CMAQ model output of NO2 with OMI derived NO2 vertical column density. As far as I know, I can use the IOAPI tool named vertot to do so. However, the vertot only sum up the NO2 concentration at different levels and the unit is still ppmv. Therefore, I wonder how can I convert the modeled NO2 concentration to the vertical column density (the unit for OMI NO2 is molec/cm2).
Any details are highly appreciated!