The photodegradation of gaseous dichloromethane(DCM) by a vacuum ultraviolet(VUV) light in a spiral reactor was investigated with different reaction media and initial concentrations.Through the combination of direct photolysis,O 3 oxidation and HO· oxidation,DCM was ultimately mineralized into inorganic compounds(such as HCl,CO 2,H 2 O,etc.) in the air with relative humidity(RH) of 75%-85%.During the photodegradation process,some small organic acids(including formic acid,acetic acid) were also detected and the intermediates were more soluble than DCM,providing a possibility for its combination with subsequent biodegradation.Based on the detected intermediates and the confirmed radicals,a photodegradation pathway of DCM by VUV was proposed.With RH 75%-80% air as the reaction medium,the DCM removal followed the second-order kinetic model at inlet concentration of 100-1000 mg/m 3.Kinetic analysis showed that the reaction media affected the kinetic constants of DCM conversion by a large extent,and RH 80% air could cause a much lower half-life for its conversion.Such results supported the possibility that VUV photodegradation could be used not only for the mineralization of DCM but also as a pretreatment before biodegradation.
