ICE NUCLEATION EFFECTS OF SOOT AND MINERAL DUST AEROSOL PARTICLES

Restricted (Penn State Only)
Author:
Alstadt, Valerie Jo
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 16, 2017
Committee Members:
  • Miriam Freedman, Dissertation Advisor
  • Miriam Freedman , Committee Chair
  • Christine Keating, Committee Member
  • Mark Maroncelli, Committee Member
  • Johannes Verlinde, Outside Member
Keywords:
  • atmospheric chemistry
  • ice nucleation
  • heterogeneous chemistry
  • DRIFTS
Abstract:
The composition and properties of aerosol particles present in the atmosphere have broad implications for both climate and human health. Aerosol particles interact with water and form cloud condensation nuclei or ice nuclei; however, the effect of these interactions on climate are not well understood. Additionally, the heterogeneous chemistry of aerosol particles can affect atmospheric particle composition and ice nucleation activity. Particle size and local aerosol composition also have important implications for human health. Of particular interest are mineral dust particles as these particles may undergo long range transport after entering the atmosphere through desert winds. These particles can interact with other atmospheric pollutants, which may alter their surface properties. We investigated the adsorption of one such pollutant, acetic acid, on the surface of the mineral kaolinite before and after the addition of water vapor using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). To determine the conformation of the resulting adsorbates on the surface, we used molecular modeling to determine the theoretical frequencies of possible surface conformations. This research determined that the type of adsorbate on the surface of the treated particles varied with the addition of water as some conformations were more energetically stable in the presence of water than others. Further work focused on water adsorption on the nanoscale and the energetics of water desorption. We studied the effects of surface defects on water adsorption on the surface of sodium chloride using Atomic Force Microscopy (AFM) and Temperature Program Desorption Spectroscopy (TPDS). This research provided insight into the energetics of how water binds to sodium chloride and how water binds onto water layers at cold temperatures. As the surface properties and composition of particles with good ice nucleation activity in the atmosphere are unclear, we also studied the immersion freezing activity of multi-walled carbon nanotubes in order to determine whether ice nucleation occurred on the outer surface, inner pore, or edge of the carbon nanotube. Using additional characterization methods, we determined that freezing occurred inside the nanotube and that freezing began at different temperatures depending on the size of the inner diameter. This research provided insight into how soot and the spherules that comprise soot could be an effective ice nucleus depending on size. On the local level, we have studied the changes in atmospheric particle composition in University Park, PA before and after local power plants converted from coal to natural gas consumption. Particle measurements were taken fourteen times in a two-year period and Transmission Electron Microscopy (TEM) was performed in order to determine how particle composition changed and whether or not the number of fractal particles changed. The long-term aim of this study was to provide specific information on the local composition of PM2.5 particles.