Continuous measurement of surface O ₃ concentration at Syowa station and Onboard Shirase

Continuous measurements of lower tropospheric ozone have been made at Syowa Station, Antarctica, since February 1988. The diurnal variation of the lower tropospheric ozone was observable only for the austral spring; variation could not be seen in the other seasons. The average amplitude of the diurnal variation reached a maximum value of about 2 ppb at most in September and October. The maximum and minimum concentrations of the diurnal variations appear before sunrise and in the afternoon, respectively. The daily mean ozone concentrations showed a clear seasonal cycle with maximum concentration in winter and minimum concentration in summer, and mean amplitude of about 20 ppb. Minimum concentrations of the seasonal cycle were almost the same for each year but maximum concentrations were variable from year to year; higher concentrations appeared in 1988 and 1990 and lower concentrations in 1989, 1991 and 1992. These variations might be ascribed to changes of the atmospheric circulation in the Antarctic. It was found that extremely low values of lower tropospheric ozone with periods of a few days appeared sporadically between August and October every year. The ozone destruction phenomenon should be related to the photochemical processes in the Antarctic atmosphere.