Heterogeneous reactions of methyl chloroform (1,1,1-trichloroethane, CH3CCl3) with alminosilica clay particles were examined between 288 and 313 K as a potential sink. Allophane and balloysite particles exhibited the activity to transform CH3CCl3 to 1,1-dichloroethene (CH2&dblbnd;CCl2). The dependence of the reaction rate on the pretreatment, temperature, and relative humidity suggested that the reaction could proceed under environmental conditions. Illumination of light with wavelength longer than 300 nm did not affect CH3CCl3 decay but caused heterogeneous degradation of CH2&dblbnd;CCl2 on clay particles. The lower limit of overall sticking coefficient for fresh allophane and halloysite particles was estimated to be 6¿10-9 and 1.1¿10-8, respectively. Heterogeneous degradation of CH3CCl3 on mineral aerosols and/or soils is worth taking into consideration in deriving tropospheric OH concentrations from global budget concentrations of CH3CCl3. ¿ 2000 American Geophysical Union