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Analyses of a dense set of lidar observations of the volcanic clouds from Mount Pinatubo and El Chichon, primarily over Boulder, Colorado, and at a wavelength of 10.59 μm, reveal notable similarities and differences. The importance of tropopause folding events for purging stratospheric debris into the troposphere is confirmed, as well as the role of gravitational settling to bring debris into the grasp of the folding mechanism. Seasonal influences appear more important than time after eruption in both poleward transport and in purging stratospheric material downward. We discuss the lengthening of the decay process for the Mount Pinatubo clouds by either an equatorial reservoir of debris or by eruptions of Mount Spurr. Simultaneous observations at 0.69 and 10.59 μm help monitor aerosol effective radii versus altitude with good temporal and vertical resolution.

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