Year-round record of near-surface ozone and O₃ enhancement events (OEEs) at Dome A, East Antarctica

Abstract. To evaluate the characteristics of near-surface O₃ over Dome A (Kunlun Station), which is located at the summit of the east Antarctic Ice Sheet, continuous observations were carried out in 2016. Together with observations from the Amundsen–Scott Station (South Pole) and Zhongshan Station, the seasonal and diurnal O₃ variabilities were investigated. The results showed different patterns between coastal and inland Antarctic areas that were characterized by high concentrations in cold seasons and at night. The annual mean values at the three stations were 29.19 ± 7.52 ppb, 29.94 ± 4.97 ppb and 24.06 ± 5.79 ppb. Then, specific atmospheric processes, including synoptic-scale air mass transport, were analysed by Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back-trajectory analysis and the potential source contribution function (PSCF) model. Long-range transport was found to account for the O₃ enhancement events (OEEs) during summer at Dome A, rather than efficient local production (consistent with previous studies in inland Antarctica). In addition, we observed OEEs during the polar night in the Dome A region, which was not previously found in Antarctica. To explain this unique finding, the occurrence of stratospheric intrusion (stratosphere-to-troposphere, STT) events was studied with the Stratosphere-to-Troposphere Exchange Flux (STEFLUX) tool. This finding suggested that STT events occurred frequently over Dome A and could account for 55 % of the total polar night period. The occurrence probability of OEEs agreed well with STT events, indicating that the STT process was the dominant factor affecting the near-surface O₃ over Dome A in the absence of photochemical reaction sources during polar night. This work provides unique information on ozone variation at Dome A and expands our knowledge regarding such events in Antarctica.