Retrieval of total column and surface NO2 from Pandora zenith-sky measurements - Zhao, X.; Griffin, D.; Fioletov, V.; McLinden, C.; Davies, J.; Ogyu, A.; Lee, S. C.; Lupu, A.; Moran, M. D.; Cede, A.; Tiefengraber, M.; Müller, M. (Atmos. Chem. Phys., 2019)