Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 3 4 2003 10.5194/acp-3-1131-2003 http://www.atmos-chem-phys.net/3/1131/2003/ http://www.atmos-chem-phys.net/3/1131/2003/acp-3-1131-2003.html http://www.atmos-chem-phys.net/3/1131/2003/acp-3-1131-2003.pdf 1131 1145 2003-08-01 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), CH-1015 Lausanne, Switzerland Using a multidiagnostic approach the rate Rev [ molec cm^-3 s^-1] or flux J_ev [ molec cm^-2 s^-1] of evaporation of H₂O and its corresponding rate constant for condensation, k_cond [s^-1 ], on a 1 µm 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 for pure ice are J_ev = 1.6 · 10 ^{28 ± 1} · exp&nbsp; (- 10.3 ± 1.2/ RT)&nbsp; [ molec cm^-2 s^-1] , k_cond = 1.7 · 10 ^{- 2 ± 1} · exp&nbsp; (+ 1.6 ± 1.5/ RT ) [s ^-1], in the presence of a HCl mole fraction in the range 3.2 · 10 ^{- 5} - 6.4 · 10 ^{- 3} : J_ev = 6.4 · 10 ^{26 ± 1} · exp&nbsp; (- 9.7 ± 1.2/ RT)&nbsp; [ molec cm^-2 s^-1] , k_cond = 2.8 · 10 ^{- 2 ± 1} · exp ( + 1.5 ± 1.6 /RT)&nbsp; [s ^-1], and a HBr mole fraction smaller than 6.4 · 10 ^{- 3} : J_ev = 7.4 · 10 ^{25 ± 1} · exp ( - 9.1 ± 1.2 /RT)&nbsp; [ 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 <font face="Symbol">D</font>H_subl = E_ev - E_cond = 11.9 ± 2.7 kcal mol^-1 , <font face="Symbol">D</font>H_subl = 11.2 ± 2.8 kcal mol^-1, and <font face="Symbol">D</font>H_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 once the fraction of the ice not contaminated by HX has evaporated.