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Interhemispheric transit time distributions and path‐dependent lifetimes constrained by measurements of SF6, CFCs, and CFC replacements

We constrain tropospheric transport from Northern Hemisphere midlatitudes to the Southern Hemisphere (SH) surface using measurements of SF6, CFCs, and CFC replacement gases and a novel maximum‐entropy‐based inversion approach. We provide the first estimate of the width Δ of the tropospheric interhemispheric transit time distribution (TTD). We find that Δ has a value of ∼1.3 years that varies little with SH latitude, compared to the mean transit time Γ that increases from ∼1.1 years in the SH tropics to ∼1.4 years at the South Pole. The TTD shape parameter Δ/Γ is thus larger in the SH tropics than at middle and high SH latitudes. Our analysis introduces a simple path‐dependent lifetime that parameterizes chemical losses. The path‐dependent lifetimes are estimated for CFC replacements, and systematic differences between path‐dependent and global lifetimes are interpreted. The path‐dependent lifetimes have the potential to provide new observational constraints on tropospheric and stratospheric loss processes.