The atmospheric chemistry of iodine is important in different environments, and particularly in case of a nuclear reactor severe accident. This paper describes the performance of an Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy (IBB-CEAS) device, based on a green LED source allowing the online detection of gaseous molecular iodine. High sensitivities and a wide dynamic range are obtained. The performances and limitations of the IBB-CEAS technique for measurements of iodine in the presence of aerosols and water vapour are discussed. The capabilities of this device to perform kinetics studies on iodine have been investigated in the framework of nuclear reactor accident research. The re-vaporization process of deposited CsI by optical monitoring of I2 concentration-time profiles is presented. The aerosols used in the experiments have been well characterized (size, distribution, concentration and mass) before interaction with iodine by a NanoScan scanning mobility particle sizer (SMPS), a PEGASOR particle sensor PPS-M and a tapered element oscillating microbalance (TEOM).