摘要：The high ice nucleating ability of some biological particles has led to speculations about
living and dead organisms being involved in cloud ice and precipitation formation, exerting
a possibly significant influence on weather and climate. In the present study, the role of
primary biological aerosol particles (PBAPs) as heterogeneous ice nuclei is investigated
with a global model. Emission parametrizations for bacteria, fungal spores and
pollen based on recent literature are introduced, as well as an immersion freezing
parametrization based on classical nucleation theory and laboratory measurements. The
simulated contribution of PBAPs to the global average ice nucleation rate is only
10 − 5%, with an uppermost estimate of 0.6%. At the same time, observed PBAP concentrations in
air and biological ice nucleus concentrations in snow are reasonably well captured by the
model. This implies that 'bioprecipitation' processes (snow and rain initiated by PBAPs)
are of minor importance on the global scale.
