On the cloud processing of aerosol particles: An entraining air‐parcel model with two‐dimensional spectral cloud microphysics and a new formulation of the collection kernel

A study has been made of the modification of marine aerosol particles due to cloud processes and the impact of the modified aerosols on the microphysical structure of future clouds. For this purpose, an entraining air‐parcel model with two‐dimensional spectral cloud microphysics was used. In order to treat collision/coalescence processes in the two‐dimensional microphysical module, a new realistic and continuous formulation of the collection kernel was developed. Based on experimental and theoretical data, the kernel covers the entire investigated size range of aerosols, cloud and rain drops, that is the kernel combines all important collision/coalescence processes such as the collision of cloud drops as well as the impaction scavenging of small aerosols by big raindrops. Since chemical reactions in the gas phase and in cloud drops have an important impact on the physico‐chemical properties of aerosol particles, the parcel model has been extended by a chemical module describing gas‐phase and aqueous‐phase chemical reactions. However, it is shown that in the numerical case‐studies presented in this paper the modification of aerosols by chemical reactions has a minor influence on the microphysical structure of future clouds. The production of large aerosol particles by collision/coalescence processes is mainly responsible for an enhanced formation of rain in a second cloud event.