Tracer‐tracer correlations: Three‐dimensional model simulations and comparisons to observations

Calculations of the stratospheric distributions of 12 trace species (N 2 O, CH 4 , CFCl 3 , CF 2 Cl 2 , CFCl 2 CF 2 Cl, CHF 2 Cl, CH 3 Cl, CH 3 CCl 3 , CCl 4 , CH 3 Br, CF 2 ClBr, and CF 3 Br) are performed by using the Goddard Institute for Space Studies/University of California at Irvine (GISS/UCI) three‐dimensional chemistry transport model (CTM). Because each of these gases is either an important precursor of ozone‐depleting radicals or a significant greenhouse molecule, it is critical that we understand their source strengths and atmospheric lifetimes. In this study, lifetimes against stratospheric loss are determined from the CTM calculations and compared with the currently accepted values. Calculated distributions of these species are compared with observations taken from aircraft platforms at midlatitudes via their correlation with N 2 O. The sensitivity of the calculated correlations to rate parameters, photolysis cross sections, and lower boundary conditions is explored for several key species. For most of the compounds examined the correlations can be simulated, within the uncertainty of the observations, by using current photochemistry. Finally, the use of correlation diagrams (i.e., scatterplots of one species versus another) as a tool for determining the lifetimes of trace gases on the basis of atmospheric observations is examined in the framework of the theory proposed by Plumb and Ko 1992.