A unique molecular beam apparatus is used to generate a beam of free clusters and nanoparticles in vacuum. Photodissociation and photochemistry of various molecules in the clusters is studied with a modern versatile UV-laser system. In this project clusters of atmospheric relevance, which play a role in, e.g., ozone depletion process, will be studied: ice nanoparticles doped with polutant molecules (hydrogen halides, HNO3, NOx, etc.). Theoretical calculations will be exploited in these studies too.