The NASA-Ames Research Center Stratospheric Aerosol Model I. Physical Processes and Computational Analogs

摘要

A time-dependent one-dimensional model of the stratospheric sulfate aerosol layer is presented. In constructing the model, a wide range of basic physical and chemical processes are incorporated in order to avoid predetermining or biasing the model predictions. The simulation, which extends from the surface to an altitude of 58 km, includes the troposphere as a source of gases and conden¬sation nuclei and as a sink for aerosol droplets. The size distribution of aerosol particles is resolved into 25 categories with particle radii increasing geometrically from 0.01 to 2.56 um such that particle volume doubles between categories. In the model, sulfur gases reaching the strato¬sphere are oxidized by a series of photochemical reactions into sulfuric acid vapor. At certain heights this results in a supersaturated H2SO4-H2O gas mixture with the consequent deposition of aqueous sulfuric acid solution on the surfaces of condensation nuclei. The newly formed solution droplets grow by heteromolecular heterogeneous condensation of acid and water vapors;the droplets also undergo Brownian coagulation, settle under the influence of gravity, and diffuse in the vertical direction. Below the tropopause, particles are washed from the air by rainfall.