Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 1 2 2001 10.5194/acpd-1-411-2001 http://www.atmos-chem-phys-discuss.net/1/411/2001/ http://www.atmos-chem-phys-discuss.net/1/411/2001/acpd-1-411-2001.html http://www.atmos-chem-phys-discuss.net/1/411/2001/acpd-1-411-2001.pdf 411 438 2001-12-13 Tropospheric NO₂ columns: a comparison between model and retrieved data from GOME measurements A. Lauer M. Dameris A. Richter J. P. Burrows DLR Institut für Physik der Atmosphäre, Oberpfaffenhofen, D-82234 Wessling, Germany Institut für Umweltphysik, Universität Bremen, D-28359 Bremen, Germany Tropospheric NO₂ plays a variety of significant roles in atmospheric chemistry. In the troposphere it is one of the most significant precursors of photochemical ozone (O₃) production and nitric acid (HNO₃). In this study tropospheric NO₂ columns were calculated by the fully coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM. These have been compared with tropospheric NO₂ columns, retrieved using the tropospheric excess method from measurements by the Global Ozone Monitoring Experiment (GOME) of up-welling earthshine irradiance and the extraterrestrial radiance. GOME is part of the core payload of the second European Research Satellite (ERS-2). For this study the first five years of GOME measurements have been used. The period of five years of observational data is sufficient to enable a comparison based on climatological averages and with global coverage, focussing on the geographical distribution of the tropospheric NO₂, for the first time. A new approach of analysing regional differences (i.e. on continental scales) by calculating individual averages for different environments provides more detailed information about specific NO_x sources and of their seasonal variations. The results obtained enable the validity of the model NO₂ source distribution and the assumptions used to separate tropospheric and stratospheric parts of the NO₂ column amount from the satellite measurements to be investigated.