Summary The air that surrounds us contains a large number of different molecules. Some molecules are harmful to human health, others play a role in formation of aerosol particles and may ultimately affect global climate via interaction of particles with light or via cloud formation. To access how molecules affect human health, air quality and climate it is important to know whether they are present in the gas phase or whether they are present in aerosol particles. We will acquire an advanced instrument (Proton Transfer Reaction Mass Spectrometer) which will allow us to identify and quantify semi-volatile organic molecules in aerosol particles as well as in the surrounding air. It will give us exciting new research possibilities and we will use it in a wide range of research projects.