A SURVEY AND NEW MEASUREMENTS OF ICE VAPOR-PRESSURE AT TEMPERATURES BETWEEN 170 AND 250K

Saturated vapor pressures of ice at temperatures below 200K have become more important since the discovery of ice clouds in the polar stratosphere and upper mesosphere. Direct measurements of ice vapor pressures at such low temperatures are sparse and unreliable. This paper summarizes published vapor pressure data and presents new measurements 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, with an accuracy of about 2%: log P = A/T + B, with A = -2663.5 +/- 0.8, B = 12.537 +/- 0.011, P in Pa and T in kelvins. Predictions by this empirical equation agree, within experimental uncertainty, with the most reliable equation derived from thermodynamic principles.