BIOGENIC AND ANTHROPOGENIC SOURCES OF ICE-FORMING NUCLEI - A REVIEW

To develop theories and numerical models of the formation and microstr ucture of clouds and precipitation, it is necessary to identify the po tential sources of ice nuclei in the atmosphere. However, the subject remains an area of debate. According to the most accepted theory, the great majority of atmospheric ice nuclei constitute soil mineral parti cles. But some evidence appears to favor the hypothesis of a nonneglig ible contribution to the population of effective ice nuclei made by bi ogenic material, living or dead. Moreover, some specific human activit ies have been identified as prolific sources of particles on which ice crystals can be generated. In contrast, it has also been suggested th at some anthropogenic effluents deactivate nuclei naturally occurring in the atmosphere. This paper summarizes present knowledge about the b iogenic and anthropogenic sources of atmospheric ice nuclei. Recent re search reveals an increasingly greater variety of sources and activiti es of ice nuclei. However intriguing and potentially significant these findings are, the overall picture emerging from the review is one of inconclusive, and sometimes contradictory, results. A standarization o f measurement techniques and a more coordinated and systematic effort in the search for a general theory of heterogeneous ice nucleation are needed to answer the fundamental questions, what is the origin of atm ospheric ice nuclei, and what is their activity spectrum?.