Abstract. Tropospheric trace gas and aerosol pollutants have adverse effects on health, environment and climate. In order to quantify and mitigate such effects, a wide range of processes leading to the formation and transport of pollutants must be considered, understood and represented in numerical models. Regional scale pollution episodes result from the combination of several factors: high emissions (from anthropogenic or natural sources), stagnant meteorological conditions, kinetics and efficiency of the chemistry and the deposition. All these processes are highly variable in time and space, and their relative contribution to the pollutants budgets can be quantified with chemistry-transport models. The CHIMERE chemistry-transport model is dedicated to regional atmospheric pollution event studies. Since it has now reached a certain level a maturity, the new stable version, CHIMERE 2013, is described to provide a reference model paper. The successive developments of the model are reviewed on the basis of published investigations that are referenced in order to discuss the scientific choices and to provide an overview of the main results.

[1] Water vapor plays an important role in the climate system through a number of mechanisms spanning a wide range of space and timescale. Since 1977, the METEOSAT satellites are equipped with a radiometer dedicated to the measurements of upper tropospheric humidity (UTH) which covers a relevant range of scales for a better understanding of the water vapor role in the climate. Due to the changes of the satellites and the calibration techniques over the last 20 years, this water vapor METEOSAT archive is not homogeneous and cannot be directly used for climatic studies. Hence the authors present in this paper a newly homogenized METEOSAT water vapor channel archive. Two main types of anomalies entail the original METEOSAT archive. The first one corresponds to the successive improvements of the calibration procedure. In this case, a statistical correction technique based on comparisons between ECMWF-simulated brightness temperature (BT) and water vapor METEOSAT-observed BT is developed. The second type of anomaly concerns the METEOSAT radiometer changes over the time. While still measuring the UTH, the details of the filter function, indeed, evolved over the last 20 years. In this second case, the correction is based on a physical method implying simulations of the same scene by different radiometer filter functions. Two major cases are documented in detail for September 1987 and for February 1994. Sensitivity analysis of the techniques is conducted and the methods are shown to be robust with respect to the details of their implementations. The efficiency of the two methods is then evaluated. The resulting archive reveals water vapor seasonal cycle features in better agreement with climatological estimates. The new homogenized METEOSAT archive consists of 3-hourly total sky radiance at the 0.625°Â 0.625°resolution over the July 1983 to February 1994 period, offering the opportunity to investigate the variability of the regional UTH from synoptic scales to interannual and interdecadal scales. INDEX TERMS: 3309

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