ALBERT

Description: It is generally known that ash particles from coal combustion can trigger ice nucleation. However, data on the ice nucleation of ash particles from different sources, including both anthropogenic and natural combustion processes, is still scarce. As coal combustion still fuels the biggest proportion of electric power production worldwide and biomass burning contributes significantly to the global aerosol loading, further data is needed to better assess the ice nucleating efficiency of ash particles. In the framework of this study, we found that ash particles from brown coal (i.e., lignite) burning are more ice active than those from wood burning, with fly ash from a coal-fired power-plant being the most efficient at nucleating ice. Furthermore the effect of particle generation on the freezing behavior was studied. For this, particles were generated either by dispersion of dry sample material, or by atomization of ash-water suspensions, and then led into the Leipzig Aerosol Cloud Interaction Simulator (LACIS) where the immersion freezing behavior was examined. Whereas the immersion freezing behavior of ashes from wood burning was not affected by the particle generation method, it depended on the type of particle generation for ash from brown coal. It was also found that the common practice of treating prepared suspensions in an ultrasonic bath to avoid aggregation of particles led to an enhanced ice nucleation activity. The findings of this study suggest a) that ash from brown coal burning may influence heterogeneous ice nucleation on at least a regional scale and b) that the freezing behavior of ash particles may be altered by a change in sample preparation and/or particle generation.