A significant natural sink for halocarbons may exist in ion-molecule reactions in the troposphere. Laboratory measurements, under conditions approximating the real atmosphere in all respects except in all except ion age, show large rate constants for removal of CCl4 and CFCl3, apparently by atmospheric ions. The rate constant for CF2Cl2 is much smaller. If the same rate constants hold for older ions, the life-times against removal by this mechanism in the atmosphere are about 41 yr for CCl4 and 70 yr for CFCl3. Under steady state conditions a sink of this magnitude may decrease the global concentration of CFCl3 by a factor two.