The ''mystery'' volcanic aerosols observed in early 1982 were produced by the eruption of Nyamuragira in eastern Zaire. Large sulfur dioxide clouds associated with this volcano were found in the total ozone mapping spectrometer data beginning on December 26, 1981, continuing into early January 1982. This fissure eruption produced 3 million tons of sulfur dioxide in clouds that rose only to the tropopause level on the basis of winds and inferred chemical loss rates (about 20%/day), which are faster than stratospheric loss rates. Two thirds of the SO2 was produced in the first 3 days of the eruption. In the 1980s this eruption was exceeded in sulfur dioxide output only by the April 1982 eruption of El Chichon. ¿ American Geophysical Union 1996