Episodes of high surface-ozone amounts at South Pole during summer and their impact on the long-term surface-ozone variation

Long-term surface-ozone and ozone-profile measurements are used to investigate the character of summertime ozone behavior at South Pole. Summer ozone profiles show a significant gradient more than 40% of the time in which mixing ratios at the surface are at least eight parts per billion by volume (ppbv) higher, and may exceed 20 ppbv higher, than mixing ratios several hundred meters above the surface. These ozone gradients are linked to very stable conditions in the boundary layer. The frequency of occurrence of these surface-ozone enhancements has varied with time with the most recent 10-year period showing a greater number of occurrences. Although the summer enhancements have influenced the overall long-term pattern of change in surface ozone, they are not the only factor. The earlier decline in surface-ozone amounts that continued into the mid 1990s was influenced by changes in other seasons as well. Surface-ozone measurements from the 1960s show that summer enhancements were a significant feature of the record at South Pole during this period. Measurements at a lower elevation inland location (Byrd Station), not on the Antarctic Plateau, do not show large summer ozone chemical production events indicating that this phenomenon is primarily confined to the plateau.