In controlled experiments carried out at Neumayer, Antarctica, throughout a diurnal cycle,concentrations of NOx (NO + NO2) were measured in air pulled through a snowblock cutfrom the Antarctic surface snow. It was found that the concentrations are higher than thosein ambient air. The production rates of NOx in the snowblock air vary with the intensity ofradiation incident on the block, consistent with photolytic mechanisms. By alternatelyshading and exposing the snowblock to sunlight, it was confirmed that photochemistrydrives the NOx production rates in the snowblock air, with, presumably, nitrate in the snowserving as the reservoir species for the production. These results provide evidence thatphotochemical activity in Antarctic surface snow can significantly increase concentrations ofNO and NO2.