DETERMINING PAST ATMOSPHERIC HCL MIXING RATIOS FROM ICE CORE ANALYSES

Laboratory and field measurements have been performed in order to impr ove our understanding of the HCl air-snow transfer function. The solub ility and diffusion of HCl in laboratory grown single crystals of ice have been measured as a function of HCl partial pressure, P-HCl, betwe en -8 and -25 degrees C. Measurements of P-HCl and of the mole fractio n 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 invol ved in the formation of snow crystals and in their evolution after dep osition are discussed in order to attempt to understand the X(HCl)' va lues and their variations. The discussion is focussed on a few well id entified snow layers. It is concluded that sublimation and recrystalli zation of snow probably play a major role in the evolution of X(HCl)', but that our understanding of the HCl transfer function is very incom plete. Laboratory and held measurements are suggested to improve this situation.