To make the specific feature of nanocrystalline silicon (nc-Si) cold cathode clear, its emission characteristics are investigated in various atmospheric gas ambiences. The experimental nc-Si diode is composed of a top thin Au film, a nanocrystallized polysilicon layer, an n(+)-type silicon wafer, and a back contact. Under operation in air, a significant current of about 1 mu A/cm(2) was detected at the collector electrode located at a distance, of I mm from the device surface. Judging from mean energy of emitted electrons, the observed current is due to electron attachment onto oxygen molecules in the proximity of the front surface. The operation stability in air has been enhanced by combining some surface treatments: high pressure water vapor annealing, forming gas (N-2+H-2) annealing, and surface bond modification. The surface-emitting nc-Si ballistic emitter is useful not only in vacuum but also in atmospheric pressures for various possible applications. (c) 2007 American Vacuum Society.