Nucleation of ice crystals in the atmosphere often occurs through heterogeneous
freezing processes facilitated by an atmospheric aerosol that acts as the ice nuclei (IN).
Depending on ambient conditions and aerosol composition, heterogeneous nucleation
will occur through one of several mechanisms including the contact and immersion
freezing mechanisms. Through a series of contact freezing experiments, we have
characterized the ability of aerosols composed of volcanic ash, soot, and peat soil, to act
as ice nuclei (IN) as a function of temperature. The immersion freezing ability of the ash
particles has also been measured. In these studies, an optical microscope apparatus
equipped with a cooling stage and a digital camera was used to observe the freezing
events. For each experiment, a particular IN was placed in contact with the surface, or
immersed in the bulk, of an ultra pure water droplet. The droplet was then subjected to
freezing-melting cycles resulting in 25 independent measurements of the freezing
temperature of the droplet. In the volcanic ash experiments, we observed contact freezing
at warmer temperatures than immersion freezing. As contact freezing IN, the peat was
the most effective with an average contact freezing temperature of -10.5 �C, followed by
volcanic ash (-11.2 �C), and then soot (-25.6 �C). In addition, we have used classical nucleation theory to identify the contact parameters and nucleation rates for the
compositions explored.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-299 |
| Date | 2009 May 1900 |
| Creators | Fornea, Adam P. |
| Contributors | Brooks, Sarah D. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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