Chlorofluorocarbons photodissociate to produce chlorine atoms, Cl•, which have been implicated in decreasing the concentration of ozone, O3, in the stratosphere. The decomposition of the ozone follows a reaction sequence of O3 + Cl• -> ClO• + O2, ClO• + O -> Cl• + O2. What role (factor affecting reaction rates) do chlorine atoms have in increasing the depletion rate of ozone?