A 3-year program for sensing the vertical profiles of debris from El Chichon in the atmosphere over Boulder, Colorado, has measured purging time constants of 208 and 60 days for the stratosphere and troposphere, respectively. No appreciable removal occurred from the atmosphere until the ''cloud'' descend to 6 km altitude 420 days after the eruptions. At a given altitude, data are lognormally distributed in time and, by assumption, in space. A simple theoretical model is offered in explanation.