Physical and optical properties of the Pinatubo volcanic aerosol: Aircraft observations with impactors and a Sun‐tracking photometer

Abstract

As determined in situ by impactor samplers flown on an ER‐2 at 16.5‐ to 20.7‐km pressure altitude and on a DC‐8 at 9.5‐ to 12.6‐km pressure altitudes, the 1991 Pinatubo volcanic eruption increased the particle surface area of stratospheric aerosols up to 50‐fold and the particle volume up to 2 orders of magnitude. Particle composition was typical of a sulfuric acid‐water mixture at ER‐2 altitudes. Ash particles coated with sulfuric acid comprised a significant fraction of aerosol at DC‐8 altitudes. Mie‐computed light extinction increased up to 20‐fold at midvisible and >100‐fold at near‐IR wavelengths. The optical thickness measured through the aerosol layer by an autotracking Sun photometer aboard a DC‐8 aircraft at 10.7‐ to 11.3‐km pressure altitudes shows a spectral shape that is similar to the Mie‐calculated spectral extinction at ER‐2 altitudes. Surface area distributions calculated by inversion of spectral optical depth measurements show characteristics that are similar to the mean surface area distribution resulting from 35 in situ measurements.