ONE-DIMENSIONAL MODEL DESCRIBING AEROSOL FORMATION AND EVOLUTION IN THE STRATOSPHERE - 2. SENSITIVITY STUDIES AND COMPARISON WITH OBSERVATIONS.

Abstract

Sensitivity tests have been performed on a one-dimensional physical-chemical dmodel of the unperturbed stratospheric aerosols and model calculations are compared with observations. The sensitivity tests and comparisons with observations suggest that coagulation controls the particle number mixing ratio, although the number of condensation nuclei at the tropopause and the diffusion coefficient at high altitudes are also important. The sulfate mass and large particle number (r greater than 0. 15 mu m) mixing ratios are controlled by growth, sedimentation, evaporation at high altitudes and washout below the tropopause. The sulfur gas source strength and the aerosol residence time are much more important than the supply of condensation nuclei in establishing mass and large particle concentrations. The particle size is also controlled mainly by gas supply and residence time. OCS diffusion (not SO//2 diffusion) dominates the production of stratospheric H//2SO//4 particles during unperturbed times.