Atmospheric aerosol particles (with sizes of a few nanometres to tens of micrometres) are key components in the climate system. Depending on their chemical composition, they are scattering or absorbing solar radiation and thus contribute to a cooling or warming of the atmosphere, respectively, and they influence cloud formation and precipitation. Aerosol particles also are a major factor in air pollution. They have been associated with respiratory and cardio-vascular diseases.

In both areas the chemical composition and reactivity of aerosol particles are important but the overall effects and many mechanistic aspects of aerosols in the atmosphere are poorly understood.