Abstract

Nitrous oxide (N₂O) and dichlorodifluoromethane (CFC-12) are the third- and fourth-most important anthropogenic greenhouse gases. Both have long atmospheric lifetimes of about 100 years and are only destroyed in the stratosphere. There, they are the most important ozone-depleting gases in terms of abundance (CFC-12) and emissions (N₂O).

Novel mass-spectrometric techniques have been developed over the last decade, which allow the detailed study of individual isotopologues and isotopomers of these gases. Strong enrichments in the heavier isotopic variants were found in stratospheric balloon and aircraft, tightly related to the degree of photochemical decomposition and the age of air. Kinetic measurements in the laboratory have provided a good understanding of the wavelength- and temperature-dependent isotopic fractionation.

The comparison between field observations and laboratory measurements provides insights into the rates of stratospheric transport and chemistry as well as the relative contributions of individual sink reactions (photolysis and photo-oxidation). The increase of the apparent isotopic fractionation with altitude and its decrease towards the poles reflects the interplay between chemistry, mixing and transport in different regions of the stratosphere.