Effect of HNO₃ and HCl on D₂O Desorption Kinetics from Crystalline D₂O Ice

Abstract

The presence of trace species may perturb H2O desorption kinetics from ice surfaces and alter the stability of atmospheric ice particles. To investigate the effects of atmospheric species on H2O desorption kinetics from crystalline ice, the D2O desorption kinetics from pure and HNO3- and HCl-dosed crystalline D2O ice multilayers on Ru(001) were investigated using isothermal laser-induced thermal desorption (LITD) measurements. The D2O desorption kinetics were studied for D2O ice film thicknesses of 25−200 BL (90−730 Å) and initial acid coverages of 0.5−3.0 BL for HNO3 and 0.3−5.0 BL for HCl. Arrhenius analysis of the D2O desorption rates from pure D2O crystalline ice at T = 150−171 K yielded a desorption activation energy of E d = 13.7 ± 0.5 kcal/mol and a zero-order desorption preexponential of νo = (3.3 ± 0.7) × 1032 molecules/(cm2 s). The absolute D2O desorption rates were ∼3−5 times smaller for D2O ice films exposed to HNO3. The D2O desorption kinetics from HNO3-dosed ice were E d = 11.3 ± 0.4 kcal/mol and νo = (5.0 ± 0.9) × 1028 molecules/(cm2 s). In contrast, the absolute D2O desorption rates were ∼2 times larger for D2O ice films exposed to HCl. The D2O desorption kinetics from HCl-dosed ice were E d = 14.2 ± 0.6 kcal/mol and νo = (3.7 ± 0.8) × 1033 molecules/(cm2 s). The changes in the D2O isothermal desorption kinetics were independent of DNO3 and DCl coverages. The adsorbate-induced perturbations are believed to be associated with the formation of stable hydrate cages and reduced D2O mobility in HNO3-dosed ice and the creation of defects and enhanced D2O mobility in HCl-dosed ice. The effects of HNO3 and HCl on the D2O desorption kinetics indicate that the growth, stability, and lifetimes of atmospheric ice particles should be altered by the presence of adsorbates on the ice surface.

Desorption kinetics of model polar stratospheric cloud films measured using Fourier Transform Infrared Spectroscopy and Temperature‐Programmed Desorption

“…These results are only in partial agreement with those of Livingston and George [28]. They found that exposing ice to HCl increases the activation barrier to ice desorption.…”

“…Another difference between the two studies is the temperature range. In the present work, the evaporation experiments were done between 170 and 180 K, slightly higher than the previous work, though there is no sign between 150 and 171 K that there should be a strong temperaturedependence to the enhancement or hindrance of ice evaporation [28]. One other difference is in how the ice was prepared.…”

“…Koehler et al [27] found that HCl•6H 2 O on ice slows the evaporation of ice. In contrast, Livingston and George [28] found that very small amounts of HCl increase the evaporation rate of ice, though the energy barrier to evaporation is increased.…”

Impact of nitric acid on ice evaporation rates

“…Our results can also be compared to very recent studies by Livingston and George [1998]. Livingston and George [1998] found that 0.3-3.0 bilayers of HNO3 adsorbed on thin ice films decreased ice evaporation rates by a factor of 3-5 over the temperature range 150-171 K. Based on our experiments, we believe this could only happen if a sealing layer formed over ice.…”

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

“…The evaporative lifetime of complex atmospheric ice particles is longer than hitherto believed owing to the slower than expected evaporation rate of H 2 O in the presence of HCl and HNO 3 (Livingston and George, 1998;Delval et al, 2003). The decrease of the absolute rate of H 2 O evaporation relative to pure H 2 O ice is a function of the amount of adsorbed trace gas and the structure of the trace gas hydrate being either in an amorphous or crystalline state.…”