We have developed a new instrument with which to study the homogeneous and heterogeneous freezing of droplets in free fall. Droplets are ejected from a generator at the top of a temperature controlled freezing tube and fall down the center of the tube as their images are recorded using video telemicroscopy. The fraction of drops frozen is measured as a function of temperature by monitoring depolarization of laser light backscattered by the falling particles.

We have tested the instrument on pure water droplets and droplets containing the bionucleant Pseudomonas Syringae, and have demonstrated the accuracy and precision of the technique. We will present results on the ice nucleation characteristics of certain sea ice bacteria as well as those of organic compounds of relevance to the tmosphere.

We find from our images that particle morphology is sensitive to freezing temperature, providing a plausible explanation for our findings (in independent experiments) that freezing mode plays a role in subsequent habit evolution.