The Infrared Radiometer experiment on the Solar Mesosphere Explorer satellite has been continuously measuring the 6.8-&mgr;m thermal emission from the stratospheric aerosol from the El Chichon volcano since the time of eruption in early April, 1982. Inversion results for the zonally-averaged infrared extinction coefficient in height, latitude, and time show that the aerosol increased in mass to a maximum of 8 Tg (8¿1012 gm) about 15 weeks after the April 4 eruption. It descended in height with an average speed consistent with the gravitational settling time of particles with a diameter of about 1.4 &mgr;m.