REanalysis of the TROpospheric chemical composition during the last 40 years Introduction In order to better understand the reasons behind the observed concentration trends of tropospheric ozone, NOx, CO, and other air pollutants, we have undertaken a 40-year reanalysis using a set of global models driven by reanalysed meteorological data from ECMWF. The project has generated new data sets of anthropogenic and wildland fire emissions. Simulations performed in RETRO contributed to multi-model assessment studies, and policy scenarios may help to elucidate the effectiveness of emission control regulations. The project has ended in the summer of 2006. A draft final report is available at ftp://ftp.retro.enes.org/pub/documents/reports. Emissions Long-term model simulations require accurate estimates of precursor emissions from anthropogenic and natural sources. New global inventories for “anthropogenic” and “fire” emissions were generated and are made available to the community. As an example, the figure below shows the annual total direct carbon emissions from forest and savanna fires and their variability. Trend Analysis Three global models of atmospheric chemistry and transport simulated the complete 41-year ERA-40 period with well constrained boundary conditions. The models often show good consistency in terms of patterns and trends, but they sometimes disagree in terms of absolute concentrations. Monthly mean summertime boundary layer (0-1 km) ozone concentrations 1960-2000 as simulated by the three RETRO long-term reanalysis simulations Policy Scenarios The RETRO models were used to estimate the effects of different policy options. Here, we show the impacts on surface NOx and ozone concentrations over Europe from a scenario where all cars in the OECD countries adhere to EURO V standards. UiO TM4 LMDz MOZECH NOx reduction Ozone change Web site: http://retro.enes.org Emissions data: ftp://ftp.retro.enes.org/pub/emissions Model data: ftp://ftp.retro.enes.org/pub/model_results Web display of model results: http://nansen.ipsl.jussieu.fr/cgi-bin/AEROCOM/retro/retro_annualrs.pl Project reports, poster, etc.: ftp://ftp.retro.enes.org/pub/documents M. G. Schultz1, S. Rast2, S. Dalsøren3, D. Hauglustaine4, S. Szopa4, T. van Noije5 and the RETRO team (contact: m.schultz@fz-juelich.de) 1) Max Planck Institute for Meteorology, Hamburg, Germany, now at Forschungszentrum Jülich, Germany 2) Max Planck Institute for Meteorology, Hamburg, Germany 3) University of Oslo, Oslo, Norway 4) Laboratoire des Sciences du Climat et de L‘Environment, CEA-CNRS Orme des Merisiers, Gif-sur-Yvette cedex, France 5) Royal Netherlands Meteorological Institute, De Bilt, The Netherlands The European Commission is kindly acknowledged for funding RETRO as project EVK2-CT-2002-00170