Developing a New Ice Nucleation Parameterization for Volcanic Ash Particles in Mixed-Phase Clouds

Annually, an average of 256 Tg of volcanic ash (VA) particles is injected into the atmosphere (Durant et al., 2010). These particles can influence air quality, aviation activities, solar radiation, cloud optical and microphysical properties (Boucher et al., 2013) as well as related atmospheric processes. Currently, the knowledge of VA ice-nucleating abilities is limited; hence, more research is required to understand the physicochemical parameters controlling their ice-nucleating activities. Here, we present new ice nucleation results from our recent study of a wide range of VA particles collected from various volcanoes. The ice nucleation properties of natural VA particles were investigated in two complementary set-ups – cloud/aerosol simulation chamber and on a cold stage. Clearly, all VA particles showed ice nucleation activity in the immersion freezing mode with ice nucleation active sites of up to 10¹¹ m^-2 at ~ 238 K. We used a principal component statistical tool to investigate the potential role of mineral and chemical compositions on the ice nucleation abilities of VA particles, which showed no direct correlation. We suggest that a synergistic contribution of different aerosol parameters might be driving the ice nucleation activity of VA particles rather than a single parameter such as mineral composition. With a collection of ice nucleation data from 20 different natural VA samples studied, we have developed an up-to-date ice nucleation parameterization for VA particles in mixed-phase cloud temperature regime. This new parameterization will be useful in modelling the role of VA particles on clouds.

Boucher, O., Randall, D., Artaxo, P., Bretherton, C., Feingold, G., Forster, P., Kerminen, V.-M., Kondo, Y., Liao, H., Lohmann, U., Rasch, P., Satheesh, S. K., Sherwood, S., Stevens, B. and Zhang, X. Y.: Clouds and Aerosols, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA., 2013.

Durant, A. J., Bonadonna, C. and Horwell, C. J.: Atmospheric and environmental impacts of volcanic particulates, Elements, 6(4), 235–240, doi:10.2113/gselements.6.4.235, 2010.