PNNL

Abstract

Ice nucleating particles (INPs) are known to affect the amount of ice in mixed-phase clouds, influencing many of their properties. The atmospheric distribution of INPs changes by orders of magnitude from terrestrial to marine environments, which typically contain lower concentrations of INP. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference, because they were developed using measurements predominantly from terrestrial environments. Biases in the INP concentrations, and the treatment of cloud glaciation as occurring equivalently for the entire globe independently of the aerosol composition, will influence the simulated amount of ice in mixedphase clouds, biasing their behaviour and affecting the climate sensitivity of climate models. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two species agrees much better with ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to neglect of INP from other terrestrial sources. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INP in models, which will guide ice nucleation researchers on where to focus future experimental work.