Tropospheric NO₂ columns: a comparison between model and retrieved data from GOME measurements

Abstract. 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 radiance and the extraterrestrial irradiance. 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 sufficiently long to facilitate for the first time a comparison based on climatological averages with global coverage, focussing on the geographical distribution of the tropospheric NO_2.

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.