Fornea, Adam P. (2009-05). Heterogeneous Surface-Based Freezing of Atmospheric Aerosols Containing Ash, Soot, and Soil. Master's Thesis. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • May 2009