The NO2 column varies greatly between background/pristine conditions (very low NO2) to very polluted urban/industrial areas (high NO2).
Yo can use operational retrievals from satellites such as OMI [https://giovanni.gsfc.nasa.gov/giovanni/#service=TmAvMp&starttime=&endtime=&data=OMNO2d_003_ColumnAmountNO2TropCloudScreened%2COMNO2d_003_ColumnAmountNO2CloudScreened&dataKeyword=no2],
GOME or SCIAMACHY [http://www.temis.nl/products/no2.html, http://www.iup.uni-bremen.de/doas/scia_no2_data_tropos.htm, http://www.sciamachy.org/products/index.php?species=NO2]