Surface-based observations of volcanic aerosol effects

Spectral optical depth measurements at Hamilton, Ontario in 1981 and 1983 are used to estimate stratospheric aerosol optical depths and a particle size distribution for the period of maximum stratospheric perturbation by aerosol due to the El Chichon eruption. Results are generally in good agreement with high altitude measurements and estimates. On average, stratospheric optical depth increased by about 0.08 with little spectral variation. Maximum aerosol enhancement occurred between January and May 1983. Mean optical depths for this period were inverted by the constrained linear inversion method of King. The resulting size distribution was similar to the haze H form of the incomplete y distribution. It compared favourably with a distribution obtained by inverting NASA CV990 optical depth measurements and was similar to estimates based on direct aerosol measurements by aircraft and balloon.