Ozone Mass-Independent Fractionation: Practical Considerations

Ozone is one of the most fascinating molecules on Earth. Besides its singular oxidative and chemical properties, ozone possesses a very unconventional oxygen isotopic composition. It is highly enriched in the oxygen heavy stable isotopes, 17O and 18O, and the isotope ratios 17O/16O and 18O/16O do not obey the mass-dependent isotope fractionation process as one would expect from the classic theory explaining the distribution of stable isotopes in matter. Instead of having an isotopic composition that scales in proportion to the mass difference between 18O and 17O 2:1 as predicted by theory, ozone shows a 1:1 ratio, accompanied by enrichments of about 100‰. Since the discovery of ozone’s strange isotopic distribution in the early 1980s, research on ozone isotope composition has taken two major directions. The first concerns investigations of the fundamental processes at the origin of this unconventional isotopic distribution that combine a mix of careful laboratory experiments and new theoretical developments. The second concerns the measurement of natural ozone found in the atmosphere and how ozone’s unconventional isotopic distribution can be inherited by other atmospheric molecules during oxidation reactions involving ozone. After a general introduction to the chemical properties of ozone, its atmospheric importance, and its first isotopic analysis, we will present the main results obtained in both directions.