A new experimental set-up for studying reactions occurring on the surfaces of materials in controlled atmospheres by InfraRed Reflection Absorption Spectroscopy (IRRAS) is presented. It consists of the reaction cell, where the sample is mounted and the in-situ investigations are carried out, a gas mixing unit, where the moist air is generated with or without corrosive gases, and an optical system coupled to the Fourier Transform InfraRed (FTIR) spectrometer (Perkin Elmer FTIR Spectrometer, Spectrum 2000). It was applied in combination with in situ Tapping Mode Atomic Force Microscopy (TM-AFM) and Phase Detection Imaging (PDI) in order to study the early stages of weathering of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ Secondary Ion Mass Spectrometry (SIMS) was carried out on the specimen after exposure. The investigations were accomplished in synthetic air with 80% Relative Humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂ and showed that an increase of the zinc content in the brass alloy yields to an increase of the corrosion formed on the metal surfaces during weathering. Additionally, investigations on pure iron as well as silver and silver-copper alloys have been carried out. This setup, which is not commercially available, proves to be a useful tool also for studying degradation processes of glass and polymers.