Scavenging waves and influence distances of gas absorption around single liquid aerosols in clouds

Scavenging wave propagation and influence distances for various gases absorbed by single liquid aerosols in the atmosphere are predicted to evaluate the effect of droplet–droplet interaction on transient mass transfer processes in clouds. Three greenhouse gases, CH4, N2O, and CO2, as well as five air pollutants, H2S, SO2, HCl, NH3, and HNO3, are taken into account. Considering the three greenhouse gases and the air pollutant H2S, because the driving forces of mass diffusion in the gas phase are by far smaller than those of the liquid phase, the gaseous scavenging behaviors in the vicinity of the droplets are absent. It thus reveals that the effect of mutual interaction of droplets on the absorption processes of these solutes is fairly slight. In regard to the other four air pollutants SO2, HCl, NH3, and HNO3, their mass diffusion numbers are relatively high, rendering that the scavenging waves in the gas phase are clearly observed in the initial uptake period. Increasing mass diffusion number makes the influence distance of the scavenging wave farther and the curvature effect along the droplet surface more pronounced. Consequently, it is recognized that the droplet–droplet interaction in clouds tends to decrease the absorption rate and elongate the uptake period as gases with large mass diffusion numbers are absorbed by droplets. In other words, the distance between cloud droplets will become an important parameter in determining the droplet absorption rate.