Atmospheric Chemistry and Physics Discussions
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3
2003
10.5194/acpd-3-2179-2003
http://www.atmos-chem-phys-discuss.net/3/2179/2003/
http://www.atmos-chem-phys-discuss.net/3/2179/2003/acpd-3-2179-2003.html
http://www.atmos-chem-phys-discuss.net/3/2179/2003/acpd-3-2179-2003.pdf
2179
2218
2003-05-08
The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: Implications for the lifetime of atmospheric ice particles
C. Delval
B. Fluckiger
M. J. Rossi
Laboratory of Air and Soil Pollution Studies (LPAS), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
Using a multidiagnostic approach the rate R<sub>ev</sub> or flux
J<sub>ev</sub>of evaporation of H<sub>2</sub>O and its condensation,
k<sub>cond</sub>, on a 1mm thick ice film have
been studied in the temperature range 190 to 240 K as well as in the presence
of small amounts of HCl and HBr that left the vapor pressure of H<sub>2</sub>O on
ice unchanged. The resulting Arrhenius expressions with RT in kcal mol<sup>-1</sup> for pure ice are
J<sub>ev</sub>=1.6×10<sup>28+/−1</sup>·exp({−10.3+\−1.2}/{RT})
[molec cm<sup>−2</sup> s<sup>−1</sup>], k<sub>cond</sub>=1.7×10<sup>−2+\-1</sup>×exp({+1.6+\−1.5}/{RT})
[s<sup>−1</sup>], in the presence of an HCl mole fraction in the range
3.2×10<sup>−5</sup>-6.4×10<sup>−3</sup>: J<sub>ev</sub>=6.4×10<sup>26+/−1</sup>×exp({−9.7+/−1.2}/{RT})
[molec cm<sup>−2</sup> s<sup>−1</sup>], k<sub>cond</sub>=2.8×10<sup>−2+/-1</sup>×exp({+1.5+/−1.6}/{RT})
[s<sup>−1</sup>], and an HBr mole fraction smaller than 6.4×10<sup>−3</sup>:J<sub>ev</sub>=7.4×10<sup>25+/−1</sup>×exp({−9.1+/−1.2}/{RT})
[molec cm<sup>−2</sup> s<sup>−1</sup>], k<sub>cond</sub>=7.1×10<sup>−5+\−1</sup>×exp({+2.6+/−1.5}/{RT})
[s<sup>−1</sup>]}. The small negative activation energy for H<sub>2</sub>O condensation on ice points to
a precursor mechanism. The corresponding enthalpy of sublimation is DH<sub>subl</sub>=E<sub>ev</sub>-E<sub>cond</sub>=11.9+/−2.7 kcal
mol<sup>−1</sup>, DH<sub>subl</sub>=11.2+/−2.8
kcal mol<sup>−1</sup>, and DH<sub>subl</sub>=11.7+/−2.8
kcal mol<sup>−1</sup> whose values are identical within experimental uncertainty
to the accepted literature value of 12.3 kcal mol<sup>−1</sup>. Interferometric data at
633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for
HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of
HX.