"Health effects due to air pollution and the potential detrimental effects of climate change are among the most important current environment-related problems. Quantifying the effect of aerosols on the planet’s radiative balance is one of the most urgent tasks in our efforts to understand future climate change. The contributions of the various aerosol sources, the role of long-range transport, and the contribution of primary and secondary particulate matter to the ambient aerosol concentrations over Europe are still largely unknown. The proposed work has two objectives: (i) Reduction of the current uncertainty of the impact of aerosol particles on climate and quantification of the relationship between anthropogenic aerosol and regional air quality. To achieve this objective, the proposed work will concentrate on the areas of greatest uncertainties. We will identify and quantify the processes and sources governing global and regional aerosol concentrations, and quantify the feedback processes that link climate change and atmospheric aerosol concentrations with emphasis on the production and loading of natural aerosols and their precursors; (ii) Development and application of a fundamental capability to simulate the indirect climatic effect of aerosols in climate models, based on integration of size-resolved treatment of tropospheric aerosols and explicit aerosol-cloud microphysics into a Global Climate Model. The proposed work will produce advanced aerosol and cloud models that can be used by global and regional climate and air quality modeling scientific communities. (i) will be achieved by improving our understanding of atmospheric aerosol physics and chemistry, which, in turn, will enhance our ability to forecast short-term regional air quality, as well as to estimate the long-term aerosol effects on the current and future global climate. (ii) will help better assess future climate change."