Samuli Urpelainen is an expert on synchrotron radiation and electron spectroscopy of atoms, molecules, clusters and surfaces. His main interests are in developing and applying novel advanced characterization methods - often synchrotron based - in studying the physical and chemical properties of matter. In particular modern in situ and operando experimental techniques give molecular level information on materials under realistic - or atmospheric - conditions. These methods, especially synchrotron radiation based x-ray photoelectron spectroscopy (XPS), give insight into the physics and chemistry of atmospheric aerosols and model systems. In his research Dr. Urpelainen applies techniques such as ambient pressure XPS (APXPS) in studying heterogeneous chemical reactions and uptake reactions on atmospherically relevant aerosols, both real and laboratory generated, under realistic conditions.