Quantification of Tropospheric Measurements from Nadir Viewing UV/Visible Instruments

In the retrieval of tropospheric NO₂ columns from space borne UV/visible measurements, the separation between stratospheric and tropospheric contributions to the signal is an essential step. Up to now, the stratospheric NO₂ column has been estimated using measurements over unpolluted regions and assuming that stratospheric NO₂ columns do not depend on longitude. In this study, several novel approaches to extract the tropospheric contribution are presented, and first applications to GOME and SCIAMACHY data are shown. The techniques studied are separation of stratosphere and troposphere using the temperature dependence of the absorption cross-section of NO₂, use of the wavelength dependence of the sensitivity to tropospheric absorptions, and use of a stratospheric chemical transport model to simulate the stratospheric NO₂.