Laboratory simulations of polar stratospheric clouds. Ph.D. Thesis
Polar stratospheric clouds (PSC`s) play a key role in stratospheric ozone depletion, making it important to understand their composition, formation and trace gas interactions. Observations of PSC`s have revealed two distinct particle populations, dubbed PSC I and II. PSC II are made up of particles of water ice, and PSC II formation can be predicted with a knowledge of ice vapor pressure at the low temperatures typical of the polar stratosphere (below 200 K). This thesis presents new measurements of ice vapor pressure at temperatures between 170 and 250 K, extending the range of measured ice vapor pressures by three orders of magnitude. A simple empirical vapor pressure equation is derived which permits prediction of vapor pressures between 170 K and the triple point of water, with an accuracy of about 2 percent. Particles that comprise type I PSC are thought to be nitric acid trihydrate, or NAT. However, recent observations of PSC I particles reveal discrepancies with laboratory data on NAT. To better understand the actual growth of PSC I particles, mixtures of water and nitric acid vapor were condensed under conditions of temperature and pressure which approximated the polar stratosphere more closely than in past studies. The resulting solids contained significantly less HNO3 than that expected of NAT, and showed considerable HNO3 supersaturation with respect to NAT. These measurements provide evidence of a previously unreported compound, nitric acid pentahydrate, which may help explain recent Arctic PSC observations. Hydrogen chloride (HCl) may react on PSCs to liberate ozone depleting chlorine, making it important to understand PSC-HCl interactions. Past investigations into the HCl-H2O-HNO3 system, however, have yielded inconsistent results. The experiments described herein measured the bulk HCl solubility in ice, NAT, and in mixtures of nitric acid and water which may also exist in the stratosphere.
- Research Organization:
- Minnesota Univ., Duluth, MN (United States). Natural Resources Research Inst.
- OSTI ID:
- 404771
- Report Number(s):
- N--96-27747; NIPS--96-07453
- Country of Publication:
- United States
- Language:
- English
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