On the use of nonmethane hydrocarbons for the determination of age spectra in the lower stratosphere

From measurements aboard that flight we derive vertical profiles of nonmethane hydrocarbons (NMHCs) and other short-lived trace gases in the lower stratosphere using Dichlorofluoromethane, CF₂ Cl₂, as the altitude scale. All profiles show an exponential decrease, which permits the description of their vertical distribution by a single parameter, the scale height.

These scale heights are shown to be related to the respective lifetimes in a unique fashion. Using the approximation of a 1-D diffusive model with a constant eddy diffusion coefficient, K, and assuming constant lifetimes, we establish an analytical solution for this relation. By fitting this theoretical expression to the experimental data we can estimate K and thus obtain an approximate age spectrum of the form given by Hall and Plumb (1994).