Temporal variations in characteristics of the El Chichón stratospheric cloud

Abstract

In situ measurements and sampling of the El Chichón eruption cloud, at 18 - 21 km altitude, were conducted over an extended period from April to December 1982, to examine the physical and chemical characteristics of the aerosol particles, their size distribution, mass concentration,morphology, and elemental composition. Within the first month after the eruption, the aerosol size distribution was dominated by salid magmatic and lithic particles, between about 3 μm and 20 μm aerodynamic diameter. In early May 1982 (1 month after the eruption), the size distribution was trimodal, with significant fractions of the mass in both the mid-size (0.5 to 3 μm) and the large-size ( > 3 μm) bands. At the upper end of the mid-size band (about 1 to 3 μm), the particles were salid but mantled in sulfuric acid, while the lower end of the band was almost totally populated by sulfuric acid droplets about 0.5 to 1.0 μm diameter. The small-size band (<0.5 μm) consisted of very fine acid droplets. There were additional features appearing at various times which are unusual far eruption aerosols. Among them are simples collected in April and May which had a nearly monodisperse band (about 1 μm to 3 μm), consisting of halite particles, which are believed to have beenfonned by the condensation of vapors from a salt dome under El Chich6fü In late July 1982, copper-zin~ -oxide particles, possiblf formed by oxidation of vapors volatized from the magma during eruption, were abundant in sizes ranging from > 20 μm to submicron sizes. Between July andDecember 1982, the <0.2 μm size band was dominated by clusters of carbonaceous particles, probably not related to the eruption but possibly ofmeteoritic origin.