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 (1) , B. Fluckiger (1) , M. J. Rossi (1)

1 Laboratory of Air and Soil Pollution Studies (LPAS)

Using a multidiagnostic approach the rate R_ev or flux J_evof evaporation of H₂O and its condensation, k_cond, 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 H₂O on ice unchanged. The resulting Arrhenius expressions with RT in kcal mol^-1 for pure ice are J_ev=1.6×10^28+/?1·exp({?10.3+\?1.2}/{RT}) [molec cm^?2 s^?1], k_cond=1.7×10^?2+\-1×exp({+1.6+\?1.5}/{RT}) [s^?1], in the presence of an HCl mole fraction in the range 3.2×10^?5-6.4×10^?3: J_ev=6.4×10^26+/?1×exp({?9.7+/?1.2}/{RT}) [molec cm^?2 s^?1], k_cond=2.8×10^?2+/-1×exp({+1.5+/?1.6}/{RT}) [s^?1], and an HBr mole fraction smaller than 6.4×10^?3:J_ev=7.4×10^25+/?1×exp({?9.1+/?1.2}/{RT}) [molec cm^?2 s^?1], k_cond=7.1×10^?5+\?1×exp({+2.6+/?1.5}/{RT}) [s^?1]}. The small negative activation energy for H₂O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DH_subl=E_ev-E_cond=11.9+/?2.7 kcal mol^?1, DH_subl=11.2+/?2.8 kcal mol^?1, and DH_subl=11.7+/?2.8 kcal mol^?1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol^?1. 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.

Domaines: Océan, Atmosphère

C. Delval, B. Fluckiger, M. J. Rossi. The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: Implications for the lifetime of atmospheric ice particles. Atmospheric Chemistry and Physics Discussions, 2003, 3 (3), pp.2179-2218. ⟨hal-00301045⟩