Stratospheric sulfuric acid fraction and mass estimate for the 1982 volcanic eruption of El Chichon

From balloon‐borne particle counter data at Laramie (41°N) and in southern Texas (27‐29°N), the total stratospheric mass of the eruptions of El Chichon is estimated to be ≈ 8 Tg about 6½ months after the eruption with possibly as much as 20 Tg in the stratosphere about 45 days after the eruption. The aerosol as observed in Texas was primarily in two layers, both highly volatile (⩾ 98%) at 150°C. Aerosol in the upper layer at ≈ 25 km was composed of an ≈ 80% H 2 SO 4 solution while the lower layer at ≈ 18 km was composed of a 60‐65% H 2 SO 4 solution aerosol. An H 2 SO 4 vapor concentration of at least 3 ×10 7 molecules cm −3 is estimated as needed to sustain the large droplets in the upper layer. An early bi‐modal nature in the size distribution suggested droplet nucleation from the gas phase during the first 3 months and similarity of the large particle profiles 2 months apart indicated continued particle growth 6½ months after the eruption. By December, the aerosol layers had largely spread to the latitude of Laramie (41°N).