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Methyl chloroform (1,1,1-trichloroethane,CH3CCl3) was found to decompose heterogeneously on seven types of standard clay minerals (23 materials) in dry airat 313 K in the laboratory. All reactions proceeded through the elimination ofHCl; CH3CCl3was converted quantitatively to CH2=CCl2. The activitiesof the clay minerals were compared via their pseudo-first-order reaction rate constants(k1). A positive correlation was observed between the k1value and the specific surface area (S) of clay minerals, where theS value was determined by means of the general Brunauer-Emmett-Teller (BET) equation. Thek1 value was anti-correlated with the value of n, which was a parameter of the general BET equation and related to theaverage pore size of the clay minerals, and correlated with the water content that canbe removed easily from the clay minerals. The reaction required no special pretreatmentof clay minerals, such as heating at high temperatures; hence, the reaction can beexpected to occur in the environment. Photoillumination by wavelengths present in thetroposphere did not accelerate the decomposition of CH3CCl3, but it inducedheterogeneous photodecomposition of CH2=CCl2. The temperature dependenceof k1, the adsorption equilibrium coefficient of CH3CCl3and CH2=CCl2, and the surface reaction rate constant ofCH3CCl3 were determined for an illite sample. The k1value increased with increasing temperature. The amount of CH3CCl3 adsorbedon the illite during the reaction was proportional to the partial pressure ofCH3CCl3. The reaction was sensitive to relative humidity and thek1 value decreased with increasing relative humidity. However, the reaction was found to proceed at a relative humidity of22% at 313 K, although the k1 value was about one-twentieth of the value in non-humidified air. The conditionsrequired for the reaction may be present in major desert regions of the world. A simple estimationindicates that the possible heterogeneous decomposition of CH3CCl3 on the ground surface in arid regionsis worth taking into consideration when inferring the tropospheric lifetime ofCH3CCl3 and global OH concentration from the global budget concentration ofCH3CCl3

Laboratory study on heterogeneous decomposition of methyl chloroform on various standard aluminosilica clay minerals as a potential tropospheric sink