Observations of the NO2 column and its diurnal variation provide an important test of aspects of stratospheric chemistry. Measurements of NO2 from two sites in the Antarctic are compared with model calculations that include a detailed treatment of diurnal NOx chemistry for fall, winter, and spring. Observed slant column amounts in spring provide strong evidence for important heterogeneous effects, probably through polar stratospheric cloud chemistry. It is shown that the slow growth of NO2 column observed during September is consistent with release of NO2 from N2O5 formed above the altitudes where polar stratospheric clouds occur. The observed early fall column amounts are in good agreement with model calculations, and the sharp onset of diurnal variation in column NO2 obtained near day 57 is well stimulated. Following this period, gas-phase model calculations suggest that N2O5 will rapidly accumulate during the Antarctic fall as nights become longer. It is suggested that the high latitude fall period during which N2O5 grows rapidly represents an optimum time to search for evidence of possible heterogeneous chemistry on background aerosols. ¿ American Geophysical Union 1992