were studied at T \ 298 K using a fast-Ñow discharge system with resonance-Ñuorescence detection of Cl atoms. The rate coefficients were found to be pressure-independent over the range 1.5È12 Torr, and were cm3 molecule~1 s~1, c m 3 molecule~1 s~1,c m 3 molecule~1 s~1 and k 4 \ (46.8 ^4.9) ] 10~12 cm3 molecule~1 s~1. The rates of reaction of these alkyl iodides with Cl atoms in k 5 \ (0.85 ^0.09) ] 10~12 the marine boundary layer were compared with the rates of their photolysis and their reaction with OH. For early morning conditions, it is shown that reaction with Cl atoms can compete with photolysis and dominate over reaction with OH, if Cl atom concentrations are about 1 ] 105 molecule cm~3. Atomic iodine may be released following reaction of Cl with the alkyl iodides ; this atomic I can participate in catalytic destruction of ozone in the marine boundary layer.