Determining past atmospheric HCl mixing ratios from ice core analyses

Abstract

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 °C. Measurements ofP HCl and of the mole fraction of HCl in snow,X'HCl, have been measured at Summit, Greenland. Comparison of the field and laboratory measurements show that theX'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 theX'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 ofX'HCl, but that our understanding of the HCl transfer function is very incomplete. Laboratory and field measurements are suggested to improve this situation.