The aim of this article is to investigate the dynamical behaviour of multiphase atmospheric chemical mechanisms. Reducing procedures are applied to a multiphase chemical box model including gas-phase reactions, aqueous-phase reactions and interfacial mass transfer. The lumping of species is computed in an automatic way using an efficient algorithm (APLA). The computed lumped species are related to the fast behaviour of chemical and microphysical processes such as Chapman cycle, ionic dissociations within the cloud drops and interfacial Henry's equilibria. Depending on some parameters (liquid water content, droplet radius) mixed lumped species (including both phases) may also be computed. We show the existence of hierarchical reduced models due to the existence of multiple timescales. We use a special algorithm (DAN2) in order to solve the reduced models. Such models are accurate and the relative error remains under the threshold of 1%. The speed-up is up to a factor 5 compared with a fully implicit method (Gear) for the same accuracy. The key point is that it provides a good qualitative understanding for the behaviour of the kinetic scheme