Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films

Abstract

Fast thermal desorption spectroscopy was used to investigate the vaporization kinetics of thin (50-100 nm) H(2)O(18) and HDO tracer layers from 2-5 microm thick polycrystalline H(2)O(16) ice films at temperatures ranging from -15 to -2 degrees C. The isothermal desorption spectra of tracer species demonstrate two distinct peaks, alpha and beta, which we attribute to the vaporization of H(2)O(18) initially trapped at or near the grain boundaries and in the crystallites of the polycrystalline ice, respectively. We show that the diffusive transport of the H(2)O(18) and HDO tracer molecules in the bulk of the H(2)O(16) film is slow as compared to the film vaporization. Thus, the two peaks in the isothermal spectra are due to unequal vaporization rates of H(2)O(18) from grain boundary grooves and from the crystallites and, therefore, can be used to determine independently the vaporization rate of the single crystal part of the film and rate of thermal etching of the film. Our analysis of the tracer vaporization kinetics demonstrates that the vaporization coefficient of single crystal ice is significantly greater than those predicted by the classical vaporization mechanism at temperatures near ice melting point. We discuss surface morphological dynamics and the bulk transport phenomena in single crystal and polycrystalline ice near 0 degrees C.

An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds

“…It is currently not known how the α values for ice and liquid H 2 O "connect" at the junction solid/liquid near 273 K, except for the work of Wei et al (2001). Measurements of α on liquid H 2 O (including a small supercooled range) suggest a negative T -dependence as well, which is in contrast to the constant T -independent value for ice reported by Lu et al (2006).…”

“…A recent measurement of the average value of α at 223 K using levitated cirrus-like ice crystals (Magee et al, 2006) found α = 6 × 10 −3 , which represents the lowest value obtained to date. Starting at 230 K α seems to increase with temperature in order to attain a value of α = 0.7 (+0.3, −0.1) in the range 259-273 K (Lu et al, 2006) for vapor-condensed ice.…”

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume V – heterogeneous reactions on solid substrates

“…The α values reported for single crystal ice by Lu et al (2006) seems to be larger than for vapor-phase polycrystalline ice (Sadtchenko et al, 2004) at 260 K which is unexpected in light of results obtained at lower temperatures (Chaix et al, 1998;Pratte et al, 2006), and considering the fact that the same technique was used in both cases.…”

“…Those that are expressed as J ev and J max ev as a function of temperature in the range 140 to 230 K have been converted to α using the vapor pressure data of Marti and Mauersberger (1993) and of Mauersberger and Krankowsky (2003). Apart from a few exceptions the consensus obtained from recent experiments seems to be that α for H 2 O on ice is significantly less than unity for T >160 K. Moreover, α decreases to 0.13 at 230 K, after which it increases again towards 273 K to attain α=0.8±0.2 at 260 K (Sadtchenko et al, 2004;Lu et al, 2006). The low temperature data of Sack and Baragiola (1993) seem to be out of line as their measured evaporation fluxes J ev consistently exceed J max ev by a factor of up to ten at 140 K and by a factor of two at 160 K for no obvious reason thus leading to α exceeding unity.…”

“…The preferred value of α in the third temperature range (230-260 K) is based on the work of Bonacci et al (1976), Sadtchenko et al (2004) and Lu et al (2006). In this range α has a positive temperature dependence that is possibly associated with the known presence of a significant quasi-liquid layer on pure ice for T ≥233 K. It is likely that α is unity at T =273 K although it has not yet been measured at this temperature.…”