Three specific objectives have been identified for INTACC: Objective 1. Determine the physical, chemical and cloud nucleating properties of the aerosol in the free troposphere over northern Europe and investigate the relationship between these properties. Objective 2. Quantify the physical and chemical processes controlling the activation or nucleation of ice particles in laer clouds and orographic clouds over northern Europe. Objective 3. Develop parametrisations of the glaciation processes in clouds for inclusion in large scale numerical models.