Evolution of the Chemical Composition of the Atmosphere over the Past Decades: Comparisons between Chemistry-Climate Model Simulations and Satellite Observations

International audienceGlobal chemistry-climate models have been used to simulate the evolution of the atmospheric composition over the past decades. These simulations have been performed using the Community Atmosphere Model included in the NCAR Community Earth System Model: this model includes a full tropospheric and stratospheric chemical scheme.We have analyzed the long-term changes as well as the interannual variability of several atmospheric compounds with a focus on ozone, carbon monoxide and nitrogen dioxide. We have investigated the behavior of these species by focusing on three regions, Europe, North America and Asia. In Europe and North America, surface emissions have decreased significantly since the 1980s, which have led to a decrease in the concentrations of several tropospheric compounds. On the contrary, emissions in Asia have dramatically increased, particularly during the past two decades, which has resulted in large increases in the atmospheric content of several species. Several issues have been raised from this analysis, i.e. an inconsistency between trends provided by different inventories of anthropogenic CO emissions in Asia and trends obtained from satellite observations since 2000. The simulations results have been compared with different satellite observations of tropospheric columns of NO2, which indicate large differences between spaceborne instruments and different retrievals of the same instrument. Differences have also been identified by the simulations in NO2 tropospheric columns since 1996 in different parts of the world, which are not always consistent with our current knowledge of surface emissions and their trends in these regions.The analysis has also used in-situ observations of O3, CO and NO2 from different monitoring networks to analyze the model results in different stations in the regions under consideration.The model simulations were performed in free-running and specified dynamic modes. The simulation with specified dynamic was forced by the Modern Era Retrospective Analysis for Research and Applications (MERRA) provided by the NASA Global Modeling and Assimialtion Office. The free-run mode includes three ensemble members with prescribed sea surface temperature and perturbed spin-up climate conditions. We will discuss comparison of tropospheric concentration of atmospheric compounds calculated by different model simulations.The results of the simulations will also be compared with results from high-resolution regional models, i.e. the CHIMERE model for Europe and the WRF-Chem model for Asia.This work is performed as part of the MACC-III (Monitoring Atmospheric Composition and Climate) European project and of the international CCMI (Chemistry-Climate Model Initiative) project