Over the years dozens of collaborators have been involved. An overarching goal of these investigations is to improve understanding of past atmospheric composition and chemistry from ice core records. In 1998 these studies discovered that extremely active photochemical processing occurs in, and just above, sunlit snow; since that time an additional focus has been to understand how "snow photochemistry" may impact the overlying atmosphere. Current projects at Summit, Greenland are specifically investigating the impact of snow emissions on coupled NOx/HOx and halogen chemistry as part of two International Polar Year (IPY) experiments, AICI and POLARCAT.