ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-4-2569-2004 Using GOME NO<sub>2</sub> satellite data to examine regional differences in TOMCAT model performance Savage N. H. 1 Law K. S. 1 3 Pyle J. A. 1 Richter A. 2 Nüß H. 2 Burrows J. P. 2 Centre for Atmospheric Science, Chemistry Department, University of Cambridge, UK Institute of Environmental Physics, University of Bremen, NW1, Kufsteiner Strasse 1, D-28359 Bremen, Germany Now at: Service d’Aeronomie, CNRS/IPSL, Paris, France 12 05 2004 4 3 2569 2613 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/4/2569/2004/acpd-4-2569-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/4/2569/2004/acpd-4-2569-2004.pdf

This paper compares column measurements of NO<sub>2</sub> made by the GOME instrument on ERS-2 to model results from the TOMCAT global CTM. The overall correlation between the model and observations is good (0.79 for the whole world, and 0.89 for north America) but the modelled columns are too large over polluted areas (gradient of 1.4 for North America and 1.9 for Europe). NO<sub>2</sub> columns in the region of outflow from North America into the Atlantic seem too high in winter in the model compared to the GOME results, whereas the modelled columns are too small off the coast of Africa where there appear to be biomass burning plumes in the satellite data. Several hypotheses are presented to explain these discrepancies. Weaknesses in the model treatment of vertical mixing and chemistry appear to be the most likely explanations. It is shown that GOME and other satellite data will be of great value in furthering our understanding of atmospheric chemistry and in targeting and testing future model development and case studies.