The CSA chamber is one of the two chambers of the CESAM platform. It is dedicated to the gas-phase atmospheric chemistry and spectroscopy studies. It is a 1m3 pyrex reactor evacuable and is operated at room temperature. It is equipped with a highly realistic artificial irradiation system and with analytical techniques including in situ long path UV-Visible and FTIR, in situ IBB-CEAS (for NO3 measurement) and PTR-Tof-MS. The CSA chamber is particularly suited for intercalibration of IR/UV spectra and study of kinetics and mechanisms of gas phase reactions.