Lunar absorption spectra have been used to determine the vertical column abundances of NO2 and NO3 above McMurdo Station, Antarctica (77.8¿S), during the fall, winter, and spring seasons in 1991. The observed nighttime NO2 and NO3 amounts during the fall and spring were broadly consistent with model predictions and with daytime measurements. During winter, local photochemistry would imply a long polar night, with associated gradual removal of NO2 and buildup of NO3 and N2O5. The winter observations of both species differ from such simple predictions by factors greater than 10, with the measured NO2 being far larger than predicted while the measured NO3 is much smaller than predicted. The concurrent measurements of both NO2 and NO3 strongly constrain possible solutions for these discrepancies and suggest that air parcel excursions to sunlit, lower latitudes likely take place quite regularly throughout the winter (approximately every 3--7 days). Thus the concept of an extended period of polar night as often applied in modeling studies of polar photochemistry appears inconsistent with these observations. ¿ American Geophysical Union 1993