Assessment of the ozone isotope effect

This chapter discusses the ozone isotope effect from a molecular perspective and presents results from atmospheric investigations. The chapter introduces a number of aspects of the oxygen-ozone system because O and O2 contribute in specific ways to the final enrichments observed in the ozone isotopologue formation. The chapter discusses the oxygen isotope exchange reaction, which plays an intrinsic role in the ozone formation. Ozone isotopes produced in natural oxygen and in specific oxygen mixtures to unfold the complexity of the effect are also explained. Further, the expression “mass-independent” is employed to characterize the ozone isotope effect in 49O3 and 50O3 and in results observed for other trace gases that may be affected by reactions with ozone. Mass independence is a descriptive label that carries little scientific information except that the process in question is not standard mass-dependent, while mass dependence in chemical and physical processes is well-defined: Molecules that have 18O substituted are about twice as much fractionated as those with 17O. The multitude of ozone isotopologues and rate coefficient ratios require a clear and precise description related to physical parameters.