Numerical simulation of chemical and physical properties of cumulus clouds

Numerical simulations have been carried out with a model consisting of aqueous chemical reactions, and dynamic and microphysical processes of cumulus clouds. The model computes temporal and spatial variations in dynamic parameters, chemical species concentrations, particle spectral evolution, and pH values for drops of different sizes. A preliminary simulation produces dynamic characteristics typical of fairweather cumulus. The in-cloud decrease in SO₂ concentration occurs mainly in the upper part of the cloud, where the decrease approaches 10%, while the corresponding SO₂ decrease in the near-cloud environment is about 2% during the 30 min of real time simulation. The dominant SO₂ oxidation pathway is kinetic oxidation by H₂O₂. For the case simulated, the droplet pH ranges between 3.5 and 5.3 for drops larger than about 20 μm in radius, while the pH of sub-μm evaporating droplets can decrease below 2.0.