Vapor pressure water, supercooled liquid from

TABLE 2-4 Vapor Pressure of Supercooled Liquid Water from 0 to 0 C ... 

Toon and Tolbert (1995) suggest that if Type I PSCs are primarily ternary solutions rather than crystalline NAT, the higher vapor pressure of HN03 over the solution would in effect distill nitric acid from Type I to Type II PSCs, assisting in denitrification of the stratosphere. This overcomes the problem that if Type II PSCs have nitric acid only by virtue of the initial core onto which the water vapor condenses, the amount of HN03 they could remove may not be very large. The supercooled H20-HN03 liquid layer observed by Zondlo et al. (1998) clearly may also play an important role in terms of the amount of HNO, that can exist on the surface of these PSCs. 

The vapor pressures of solid and liquid water as a function of temperature. The data for liquid water below 0°C are obtained from supercooled water. The data for solid water above 0°C are estimated by extrapolation of vapor pressure from below 0°C. 

Due to the lower vapor pressure of the solids compared to supercooled liquids of the same temperature, frozen aerosol particles grow rapidly by condensation of water and nitrous oxides and are removed from the stratosphere by deposition if their size exceeds about 10 m. Under antarctic conditions this effect can lead to a permanent removal of nitrogen oxides from the stratosphere a process which is known as denitrification. 

IAPWS-95 is now the state of the art and the international standard for representing water s thermodynamic properties at temperatures from its freezing point to 1000°C and at pressures up to 1000 MPa. It also extrapolates in a physically meaningful manner outside this range, including the supercooled liquid water region. The uncertainties in the properties produced by IAPWS-95 are comparable to those of the best available experimental data this is quite accurate in some cases (for example, relative uncertainty of 10 for liquid densities at atmospheric pressure and near-ambient temperatures) and less so where the data are less certain (for example, relative uncertainty of 2 x 10 for most vapor heat... 

Figure 8. Left panel phase diagram of ice T> T (P)) and transition lines corresponding to the ice Ih-to-HDA, LDA-to-HDA, and HDA-to-LDA transformations T

Supercooled (metastable) water vapor commonly occurs in the atmosphere if dust particles are not present to begin condensation to the liquid. Sometimes small particles, such as tiny crystals of silver iodide, are released from airplanes in an attempt to begin condensation. This process is called cloud seeding. At a certain location, water vapor at 25°C has a metastable partial pressure of 32.0 torr. The equilibrium value at this temperature is 23.756 torr. Consider the air that is present to be the surroundings, and assume it to remain at equilibrium at 25°C. A tiny particle is added to begin condensation. Calculate AS, A//, and ASgurr per mole of water that condenses. State any assumptions. 

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