We analyze data (Telegadas, 1974, 1976) on the transport of 95Zr from five Chinese 3-Mt thermonuclear explosions which deposited their debris clouds at approximately 18-km altitude and location (40¿N, 90¿E) in terms of one-dimensional diffusive transport into the troposphere. The motivation for the work is that the dynamics of oxides of nitrogen and other materials injected into the lower stratosphere by supersonic transport aircraft in the general region of 15- to 18-km altitude, 40¿-60¿N latitude, is not well known, and different parameterizations of the transport by different authors vary substantially. A technique is developed here that allows data from pulsed sources at different seasons to be used to parameterize stratospheric motions in terms of a mean stratospheric eddy diffusivity ? and a mean tropopause height z0 (which characterizes an effective height of injection above the local tropopause) and thus to estimate the atmospheric residence time (equal to burden divided by flux) and also the 'injection coefficient' of McElroy et al. (1974) for continuous sources. A correction is made for the sedimentation of the particulate tracers used.