Atmospheric aerosol particles and trace gases affect the quality of our life in many ways (e.g. health effects, changes in climate and hydrological cycle). Trace gases and atmospheric aerosols are tightly connected via physical, chemical, meteorological and biological processes occurring in the atmosphere and at the atmosphere-biosphere interface. One important phenomenon is atmospheric aerosol formation, which involves the production of nanometer-size particles by nucleation and their growth to detectable sizes. The main scientific objectives of this project are 1) to quantify the mechanisms responsible for atmospheric new particle formation and 2) to find out how important this process is for the behaviour of the global aerosol system and, ultimately, for the whole climate system. Our scientific plan is designed as a research chain that aims to advance our understanding of climate and air quality through a series of connected activities. We start from molecular simulations and laboratory measurements to understand nucleation and aerosol thermodynamic processes. We measure nanoparticles and atmospheric clusters at 15-20 sites all around the world using state of the art instrumentation and study feedbacks and interactions between climate and biosphere. With these atmospheric boundary layer studies we form a link to regional-scale processes and further to global-scale phenomena. In order to be able to simulate global climate and air quality, the most recent progress on this chain of processes must be compiled, integrated and implemented in Climate Change and Air Quality numerical models via novel parameterizations.