Volatility of Amorphous Solid Water.

Area of Science:

• Cosmic ice physics
• Planetary science
• Atmospheric science

Background:

• Amorphous solid water is the most abundant solid water form in the universe.
• Its thermodynamic properties, including saturation vapor pressure, are not well-established.
• Accurate data is crucial for understanding astrophysical and atmospheric phenomena.

Purpose of the Study:

• To experimentally determine the saturation vapor pressure over vapor-deposited amorphous ice.
• To investigate the thermodynamic properties of amorphous solid water.
• To refine models of ice cloud formation in planetary atmospheres and space.

Main Methods:

• Utilized a novel experimental method measuring mass growth rates of ice-covered nanoparticles.
• Operated under supersaturated water vapor conditions at temperatures between 133 and 147 K.
• Determined absolute vapor pressures and sublimation rates of amorphous solid water.

Main Results:

• Found saturation vapor pressure of amorphous solid water to be up to 3 times higher than current parameterizations.
• Reconciled calorimetric measurements by identifying nanocrystalline ice as an intermediate phase during amorphous ice crystallization.
• Proposed a new enthalpy of crystallization for amorphous solid water (ΔH = 2312 ± 227 J/mol).

Conclusions:

• The higher vapor pressure of amorphous solid water necessitates revisions to existing models.
• Findings impact understanding of water ice clouds on Mars and Earth's mesosphere.
• Results may alter interpretations of stratospheric ice formation processes.