Good morning D,
There is no basic knowledge unless you have mastered it first! So don’t worry at all about asking questions, this forum is the best place for it, no judgements and Sander is excellent in replying to all bizarre questions we pose him.
I think there is a slight confusion with the units in your question. You mention the question I posed here, S5P CH4 | Column ppb to column number density mol/m2 conversion, which however relates to how the CH4 product is being retrieved from the data. One can translate volume mixing ratio to number density, and vice versa, but it is not trivial to translate column density to ppm/ppb.
The product you require I think is the tropospheric_NO2_column_number_density check here: S5P_L2_NO2 — HARP 1.12 documentation (stcorp.github.io)
However this product is provided in mol/m2 and to translate this into ppm [i.e. a surface concentration] you require input from a chemical transport model.
Please also read previous threads:
Convert the unit from molecules/m^2 to ppm - Atmospheric Toolbox
and
Map Sentinel 5p CH4, SO2 and CO Data (Visan) - HARP - Atmospheric Toolbox
Good luck!
MariLiza