Variations of tropospheric ozone concentration over Syowa Station, Antarctica

Aircraft measurements of the tropospheric O 3 concentration were made over Syowa Station (69°00'S, 39°35'E), Antarctica from May 1989 to January 1990, except during the polar night months of June and July. The O 3 concentration increased with height for the whole period of the measurements. Lower tropospheric O 3 showed a prominent seasonal variation with maximum concentration in winter and minimum concentration in summer, which is very close to the result of continuous O 3 measurements initiated at Syowa Station in February 1988. In the upper troposphere, the concentration reached high values in winter, decreased gradually until late spring and then increased again. As a result, the height-dependent difference of the concentration was reduced from late autumn to early spring and enhanced in remaining seasons of the year. The seasonal variation of upper tropospheric O 3 was similar to those of the lower stratospheric O 3 concentration measured by ozonesondes and the total amount of O 3 by a Dobson spectrophotometer over Syowa Station. Inspection of TOMS (Total Ozone Mapping Spectrometer) data also suggested that the temporal variations of the upper tropospheric O 3 measured in this study are closely related to those of the lower stratospheric O 3 over Syowa Station. Comparison of the results of surface O 3 measurements in the southern hemisphere showed that the concentration increase going southward, and appearance of the minimum concentration of the seasonal variation is delayed by almost 1 month at the South Pole compared to Syowa Station and Cape Grim, Tasmania. Taking into account these results, it is suggested that the intrusion of stratospheric O 3 into the troposphere occurs over Syowa Station throughout the year, and that air with low O 3 concentrations is transported from subpolar or middle latitudes to the station through the lower troposphere from spring to early autumn, in addition to the photochemical destruction of O 3 near the station.