Reanalysis of the chemical composition of the troposphere for the period 1980-2005 using the chemistry aerosol general circulation model ECHAM5-HAMMOZ. The global composition of the troposphere is highly influenced by the total amount and geographical distribution of trace gas and aerosol emissions, which have changed significantly during the last 30 years. While Europe and the US started to define and to apply strategies to enhance air quality, the emission rates in economically emerging countries, such as China and India, increased significantly. Understanding past trends of the concentrations and distributions of trace gases and aerosols in the troposphere is a key point to evaluate the efficiency of the exisiting strategies to reduce air pollution and to define more efficient strategies for the future. We performed a simulation of the period 1980-2005 with the chemistry aerosol general circultion model ECHAM5-HAMMOZ to understand and assess long term changes and interannual variability of the chemical composition of the troposphere. The model includes simulations of the NOx-Ox-hydrocarbon chemistry and of the aerosol chemistry and microphysics, the two simulations being embedded into the well established general circulation model ECHAM5.