Abstract
Immersion freezing is an important heterogeneous ice nucleation process
in mixed-phase clouds. Many researches on immersion freezing focus on
the parameterization using the classical nucleation theory. However, the
ice nucleating abilities of the atmospheric aerosol particles are not
well understood, and therefore cause difficulties of the
parameterization of immersion freezing. In this study, we investigate
the ice nucleating ability of Marigold pollen from the Beijing area by
doing drop immersion freezing experiments in the laboratory. Marigold
pollen are first mixed with pure water. A population of drops with a
volume of 10 mL from the mixture are then put on a PE film in a chamber
with a cooling rate of about 0.5 °C min-1. We find that the median
freezing temperature of drops with pollen as ice nuclei is -17 °C. The
contact angle parameterization of immersion freezing using the classical
nucleation theory is also given in this study. We use the single-θ and
the θ-pdf parameterization schemes to explain the data. The results show
that the θ-pdf parameterization scheme is better for describing the ice
nucleating behavior of the pollen in Beijing.