# How to convert $\ce{NO2}$ mixing ratio (ppmv) into $\ce{NO2}$ column density(moles/m2)?

I have a WRF-chem output with NO2 mixing ratio for 37 levels, for my analysis I need to convert it into into column density. How do I do that?

• There are post process calculators that can do this for you easily. However, if you are planning to compare to satellite retrievals, you are supposed to use the averaging kernels from the satellite instrument algorithm. Calculating the column density with the satellite averaging kernels creates a large computational burden and requires many QA/QC steps for the satellite data. So, the answer to your question really depends on your application.
– f.thorpe
Nov 11, 2021 at 4:56
• i am trying to convert the mixing ratios into column density so that i can use it as an a priori in VCD data retrievel in TROPOMI instead of the TM5 profile Nov 11, 2021 at 5:28
• also is it possible to get the WRF-Chem output in the form of column density rather than in the form of mixing ratios? Nov 11, 2021 at 5:31
• the a priori for TROPOMI should be a profile... not a VCD, right? I've never heard of an a priori VCD...
– f.thorpe
Nov 11, 2021 at 16:04
• Sorry I'm not a WRF-CHEM user, CMAQ has a program called PHOTDIAG that does it and a models-3 program called VERTINTEGRAL can do it. Though, there is a nice explanation of the simple mathematics here: forum.wrfforum.com/viewtopic.php?f=41&t=5552#p19541
– f.thorpe
Nov 11, 2021 at 16:18