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We present results of experiments at the aerosol interactions anddynamics in the atmosphere (AIDA) chamber facility looking at thefreezing of water by three different types of mineral particles attemperatures between −12°C and−33°C. The three different dusts are Asia Dust-1(AD1), Sahara Dust-2 (SD2) and Arizona test Dust(ATD). The dust samples used had particle concentrations of sizesthat were log-normally distributed with mode diameters between 0.3 and0.5 μm and standard deviations, σ<sub>g</sub>, of1.6–1.9. The results from the freezing experiments are consistent withthe singular hypothesis of ice nucleation. The dusts showed differentnucleation abilities, with ATD showing a rather sharp increase inice-active surface site density at temperatures less than−24°C. AD1 was the next most efficient freezingnuclei and showed a more gradual increase in activity than theATD sample. SD2 was the least active freezing nuclei.  We used data taken with particle counting probes to derive theice-active surface site density forming on the dust as a function oftemperature for each of the three samples and polynomial curves arefitted to this data. The curve fits are then used independently withina bin microphysical model to simulate the ice formation rates from theexperiments in order to test the validity of parameterising the datawith smooth curves. Good agreement is found between the measurementsand the model for AD1 and SD2; however, the curve forATD does not yield results that agree well with theobservations. The reason for this is that more experiments between−20 and −24°C are needed to quantify the rathersharp increase in ice-active surface site density on ATD in thistemperature regime. The curves presented can be used asparameterisations in atmospheric cloud models where cooling rates ofapproximately 1°C min<sup>−1</sup> or more are present topredict the concentration of ice crystals forming by thecondensation-freezing mode of ice nucleation. Finally a polynomial isfitted to all three samples together in order to havea parameterisation describing the average ice-active surface sitedensity vs. temperature for an equal mixture of the three dustsamples

Studies of heterogeneous freezing by three different desert dust samples