THERMODYNAMICS AND KINETICS OF THE SOLID-SOLUTION OF HCL IN ICE

The equilibrium solubility of HCl in ice I-h has been measured as a fu nction of temperature and HCl partial pressure, between -8 and -35 deg rees C by doping large ice single crystals with gaseous HCl for severa l weeks. Results indicate that the solubility of HCI in ice is very lo w, much less than found in many previous studies. Its temperature and HCl partial pressure dependences are found to be X-HCl = 6.13 x 10(-10 )e(2806.5/T) (P-HCl)(1/2.73) where X-HCl is the solubility in mole fra ction, P-HCl is the HCl partial pressure in Pa, and T is the temperatu re in kelvin. The diffusion coefficient of HCl in ice is also found to be very low, about 10(-12) cm(2)/s at -15 degrees C. Extrapolations o f these data yield the solidus in the temperature-composition phase di agram. The determination of the solid phase composition in equilibrium with a given gas phase composition allows the calculation of the part ial enthalpy of sublimation of HCl from ice, Delta h(HCl)(s) = 63.7 +/ - 7.6 kJ/mol, and of the activity of HCl in ice. Possible mechanisms o f HCl incorporation in ice are discussed. Atmospheric implications con cerning ozone depletion and the understanding of snow composition are examined.