Abstract: GPSO₃ ozonesondes have been used to characterize the vertical distribution of atmospheric ozone over Beijing.Based on the ozone sondes data from September of 2002 to December of 2012, seasonal ozone variation and variability near the tropopause level is highlighted.The results indicate that the ozone mixing ratio increases with the altitude through the troposphere in all seasons.Generally, the averaged ozone concentration is the highest in summer and lowest in winter through the troposphere, and it is almost same in spring and autumn.Ozone concentration has a few differences in different height ranges.Vertical distribution and average of ozone concentration in the upper troposphere and lower stratosphere (8-15 km) is strongly modulated by the location of the tropopause.Analysis of tropopause-based coordinate suggests that vertical distribution of ozone concentration in the altitudes of 1-3 km under the tropopause is similar to that in the tropopause, while seasonal ozone concentration increases significantly with the heights near the tropopause.Due to increase of ozone concentration with altitude in different seasons, seasonal variation of ozone concentration in the altitudes of 1-3 km above tropopause is quite different from that in the troposphere.Normalized standard deviation of ozone concentration suggests that ozone variability is the highest in winter, followed in autumn, spring and summer in the lower troposphere, while it is the highest in spring, followed in winter, autumn and summer near the tropopause.The strong ozone variability around the tropopause in spring and winter is very likely related to active atmospheric disturbances and tropopause height variation in these seasons.

Key words: Ozonesonde data, Tropopause, Stratosphere, Seasonal variability