Rates of aerosol-mediated reactions involving inorganic halogen species are small but non-negligible for moderate aerosol abundances at temperatures of 200--210 K. We have used a photochemical model to demonstrate that at these temperatures such reactions provide a significant sink for HCl. Gas-phase production rates are slower for HCl than for ClNO3. The net result is perferential partitioning of Cly into [ClNO3> to compensate for the accelerated loss of [HCl>. Under such conditions, [HNO3> decreases in response to enhanced partitioning of NOy into [ClNO3>. The results indicate a high sensitivity and synergistic response of HCl, ClNO3, and HNO3 distributions to aerosol content and temperature ¿ 1999 American Geophysical Union