Laboratory simulations of polar stratospheric clouds
Polar stratospheric clouds (PSCs) play a key role in stratospheric ozone depletion, making it important to understand their composition, formation and trace gas interactions. Observations of PSCs have revealed two distinct particle populations, dubbed PSC I and II. PSC II are made up of particles of water ice and formation can be predicted with a knowledge of ice vapor pressure at the low temperatures typical of the polar stratosphere (below 200K). This thesis presents new measurements of ice vapor pressure at temperatures between 170 and 250K, 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 170K and the triple point of water. 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. Mixtures of water and nitric acid vapor were condensed under conditions of temperature and pressure studies. The resulting solids contained significantly less HNO[sub 3] than that expected of NAT, and showed considerable HNO[sub 3] 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. 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. The results show a strong dependence of the HCl solubility on the HNO[sub 3] content in ice particles. These measurements also allowed estimates of HCl surface coverage on PSCs and of the diffusion coefficient of HCl in ice, both important virtues for ozone depletion modeling.
- Research Organization:
- Minnesota Univ., Minneapolis, MN (United States)
- OSTI ID:
- 6882297
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
540120* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
ATMOSPHERIC CHEMISTRY
BENCH-SCALE EXPERIMENTS
CHEMISTRY
CHLORINE COMPOUNDS
CLOUDS
CRYOSPHERE
EARTH ATMOSPHERE
HALOGEN COMPOUNDS
HYDROCHLORIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
LAYERS
NITRIC ACID
OZONE LAYER
POLAR REGIONS
SIMULATION
STRATOSPHERE