The main objective is to study the importance of aerosol particles on climate change and on human health. Particularly, the focus will be on the effect of biogenic aerosols on global aerosol load. During the recent years it has become obvious that homogeneous nucleation events of fresh aerosol particles take frequently place in the atmosphere, and that homogeneous nucleation and subsequent growth have significant role in determining atmospheric aerosol load. In order to be able to understand this we need to perform studies on formation and growth of biogenic aerosols including a) formation of their precursors by biological activities, b) related micrometeorology, c) atmospheric chemistry, and d) atmospheric phase transitions. Our approach covers both experimental (laboratory and field experiments) and theoretical (basic theories, simulations, model development) approaches.