The influence of HCl on the evaporation rates of H 2 O over water ice in the range 188 to 210 K at small average concentrations
2018
Abstract. The evaporation flux J ev ( H 2 O ) of H 2 O
from HCl -doped typically 1.5 µm or so thick vapor-deposited
ice films has been measured in a combined quartz crystal
microbalance (QCMB)–residual gas mass spectrometry (MS) experiment.
J ev ( H 2 O ) has been found to show complex behavior and to
be a function of the average mole fraction χ HCl of HCl in
the ice film ranging from 6×10 14 to
3×10 17 molecule cm −2 s −1 at 174–210 K for initial
values χ HCl 0 ranging from 5 × 10 - 5 to
3 × 10 - 3 at the start of the evaporation. The dose of HCl on
ice was in the range of 1 to 40 formal monolayers and the H 2 O vapor
pressure was independent of χ HCl within the measured range and
equal to that of pure ice down to 80 nm thickness. The dependence of
J ev ( H 2 O ) with increasing average χ HCl was
correlated with (a) the evaporation range r b∕e
parameter, that is, the ratio of J ev ( H 2 O ) just before HCl
doping of the pure ice film and J ev ( H 2 O ) after observable
HCl desorption towards the end of film evaporation, and (b) the
remaining thickness d D below which J ev ( H 2 O )
decreases to less than 85 % of pure ice. The dependence of
J ev ( H 2 O ) with increasing average χ HCl from
HCl -doped ice films suggests two limiting data sets, one associated
with the occurrence of a two-phase pure ice/crystalline HCl hydrate binary
phase (set A) and the other with a single-phase amorphous HCl∕H 2 O
binary mixture (set B). The measured values of J ev ( H 2 O )
may lead to significant evaporative lifetime extensions of
HCl -contaminated ice cloud particles under atmospheric conditions,
regardless of whether the structure corresponds to an amorphous or
crystalline state of the HCl∕H 2 O aggregate.
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