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Based on the outcome of laboratory results, new particle-dependentparameterizations of heterogeneous freezing were derived and used to improveand extend a two-dimensional spectral microphysics scheme. They include (1)a particle-type-dependent parameterization of immersion freezing using thenumbers of active sites per mass, (2) a particle-type and size-resolvedparameterization of contact freezing, and (3) a particle-type-dependentdescription of deposition freezing. The modified microphysical scheme wasembedded in an adiabatic air parcel model with entrainment. Sensitivitystudies were performed to simulate convective situations and to investigatethe impact of ice nuclei concentrations and types on ice formation. As acentral diagnostic parameter, the ice water fraction (IWF) was selected, which isthe relation of the ice water content to the total amount of water inthe condensed form. The following parameters were varied: initial aerosolparticle number size distributions, types of ice nucleating particles, finaltemperature, and the fractions of potential ice nucleating particles. Singleand coupled freezing processes were investigated. The results show thatimmersion freezing seems to be the most efficient process. Contact freezingis constrained by the collision kernel between supercooled drops andpotential ice nucleating particles. The importance of deposition freezinglies in secondary ice formation; i.e., small ice particles produced bydeposition nucleation trigger the freezing of supercooled drops bycollisions. Thus, a broader ice particle spectrum is generated than that byimmersion and contact freezing. During coupled immersion–contact andcontact–deposition freezing no competition was observed, and both processescontribute to cloud ice formation but do not impede each other. As alreadysuggested in the literature, mineral dust particles seem to be the mostimportant ice nucleating particles. Biological particles are probably notinvolved in significant ice formation. The sensitive parameters affectingcloud properties are temperature, aerosol particle composition andconcentration, and particle size distribution

New particle-dependent parameterizations of heterogeneous freezing processes: sensitivity studies of convective clouds with an air parcel model