The reaction of ozone with oxygen atoms in the presence of chlorine atoms can occur by a two step process shown below:
$$O_3(g) + Cl^\bullet \to O_2(g) + ClO^\bullet(g)$$ ...(i)
$$k_i = 5.2 \times 10^9$$ L mol$$^{-1}$$ s$$^{-1}$$
$$ClO^\bullet(g) + O^\bullet(g) \to O_2(g) + Cl^\bullet(g)$$ ...(ii)
$$k_{ii} = 2.6 \times 10^{10}$$ L mol$$^{-1}$$ s$$^{-1}$$
The closest rate constant for the overall reaction
$$O_3(g) + O^\bullet(g) \to 2O_2(g)$$ is:

In a multi-step reaction mechanism, the overall rate is determined by the rate-determining step (RDS), which is the slowest step in the sequence. For such a mechanism, the effective rate constant of the overall reaction is approximately equal to the rate constant of the RDS.

By comparing the rate constants, we see that $$k_i$$ ($$5.2 \times 10^9$$) is significantly smaller than $$k_{ii}$$ ($$2.6 \times 10^{10}$$). Since step (i) is the slower process, it acts as the rate-determining step.