Parameterization of In-Cloud Aerosol Scavenging Due to Atmospheric Ionization: Part 4. Effects of Varying Altitude

We have verified that the modified analytic solution (MAS) for aerosol scavenging designed in our previous work to parameterize in-cloud collision rate coefficients between aerosol particles and droplets can be extended to altitudes ranging from 0 to 20.6 km, and droplet radii up to 100 μm. The MAS deals separately with the short-range effects and long-range effects involved in the collisions, with the short-range effects including image electric forces, the intercept effect, and the weight effect; and the long-range effects including Brownian diffusion, the Coulomb electric force, and phoretic forces. The effects of Brownian diffusion and Coulomb electric force increase as height increases, while the change of phoretic forces with altitude is complicated. The effects of image electric force and intercept change slightly with altitude, while the weight effect increases significantly at higher altitudes. When the short-range effects include the irregular shape of particles, the MAS also works well. The calculations of collision rate coefficients by our Monte Carlo trajectory model for varying droplet radius, droplet charges, particle radius, particle charges, particle density, relative humidity, pressure and temperature have now been completed, and we parameterize them by the simple MAS method which makes the results user friendly and easily applicable for cloud models. Based on our results, it is now possible to build cloud models to investigate the hypothesized link between the downward current flow in the global electric circuit current and cloud microphysical changes affecting cloud development.