Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 4 7 2004 10.5194/acp-4-1895-2004 http://www.atmos-chem-phys.net/4/1895/2004/ http://www.atmos-chem-phys.net/4/1895/2004/acp-4-1895-2004.html http://www.atmos-chem-phys.net/4/1895/2004/acp-4-1895-2004.pdf 1895 1912 2004-09-16 Using GOME NO₂ satellite data to examine regional differences in TOMCAT model performance N. H. Savage K. S. Law J. A. Pyle A. Richter H. Nüß J. P. Burrows 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 This paper compares column measurements of NO₂ 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 larger than GOME over polluted areas (gradient of 1.4 for North America and 1.9 for Europe). NO₂ columns in the region of outflow from North America into the Atlantic are higher in winter in the model compared to the GOME results, whereas the modelled columns are smaller 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.