The column amounts of NO2 have been measured using visible spectroscopy at Syowa Station, Antarctica (69 ¿S), from March 1990. The NO2 slant column amount at a solar zenith angle of 90¿ exhibits a large seasonal variation reaching the minimum value of 1¿1016 cm-2 or less in midwinter, and it increases to the maximum value of 17¿1016 cm-2 in midsummer. The recovery of NO2 in spring is 2--3 times slower than the fall decay. The observed temperature indicates that polar stratospheric clouds (PSCs) are expected to form from midwinter to early spring. A decrease in ozone was observed from early August and continued to the end of September, which is consistent with the observed depletion in NO2 during the same period. A chemical box model has been used to interpret quantitatively these observed results. The observed NO2 values in fall are in agreement with the box model including only gas phase chemistry or with heterogeneous chemistry on background sulfuric acid aerosols. In addition, the very low NO2 amounts and slow rate of increase observed from midwinter to early spring agree well with the model results assuming heterogenous chemistry on PSCs. From the late spring of 1991 the NO2 amounts are lower by more than 30%, presumably due to the increased rate of conversion of NOx into HNO3 via N2O5 on the enhanced amount of sulfuric acid aerosols resulting from the Pinatubo eruption. The reduction of NO2 levels in midsummer of 1991 and 1992 below those of midsummer in 1990 is probably due to the transport of air from lower latitudes, where NO2 is already reduced by the volcanic aerosols. NO2 and O3 values in October 1992 were much reduced as compared with those for 1990 and 1991, reflecting the difference in the location of the vortex boundary relative to Syowa Station. ¿ American Geophysical Union 1994