DETERMINING PAST ATMOSPHERIC HCL MIXING RATIOS FROM ICE CORE ANALYSES

Laboratory and field measurements have been performed in order to improve our understanding of the HCl air-snow transfer function. The solubility and diffusion of HCl in laboratory grown single crystals of ice have been measured as a function of HCl partial pressure, P-HCl, between -8 and -25 degrees C. Measurements of P-HCl and of the mole fraction of (HCl) in snow, X(HCl)', have been measured at Summit, Greenland. Comparison of the held and laboratory measurements show that the X(HCl)' values are well below equilibrium values. The major processes involved in the formation of snow crystals and in their evolution after deposition are discussed in order to attempt to understand the X(HCl)' values and their variations. The discussion is focussed on a few well identified snow layers. It is concluded that sublimation and recrystallization of snow probably play a major role in the evolution of X(HCl)', but that our understanding of the HCl transfer function is very incomplete. Laboratory and held measurements are suggested to improve this situation.