Year-round record of near-surface ozone and O-3 enhancement events (OEEs) at Dome A, East Antarctica

Dome A, the summit of the East Antarctic Ice Sheet, is an area challenging to access and is one of the harshest environments on Earth. Up until recently, long-term automated observations from Dome A (DA) were only possible with very low power instruments such as a basic meteorological station. To evaluate the characteristics of near-surface O-3, continuous observations were carried out in 2016. Together with observations at the Amundsen-Scott Station (South Pole - SP) and Zhongshan Station (ZS, on the southeast coast of Prydz Bay), the seasonal and diurnal O-3 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 (DA, SP and ZS) were 29.2 +/- 7.5, 29.9 +/- 5.0 and 24.1 +/- 5.8 ppb, respectively. We investigated the effect of specific atmospheric processes on near-surface summer O-3 variability, when O-3 enhancement events (OEEs) are systematically observed at DA (average monthly frequency peaking at up to 64.5% in December). As deduced by a statistical selection methodology, these O-3 enhancement events (OEEs) are affected by significant interannual variability, both in their average O-3 values and in their frequency. To explain part of this variability, we analyzed the OEEs as a function of specific atmospheric processes: (i) the role of synoptic-scale air mass transport over the Antarctic Plateau was explored using the Lagrangian back-trajectory analysis Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) method, and (ii) the occurrence of "deep" stratospheric intrusion events was investigated using the Lagrangian tool STEFLUX. The specific atmospheric processes, including synoptic-scale air mass transport, were analyzed by the HYSPLIT back-trajectory analysis and the potential source contribution function (PSCF) model. Short-range transport accounted for the O-3 enhancement events (OEEs) during summer at DA, rather than efficient local production, which is consistent with previous studies of inland Antarctica. Moreover, the identification of recent (i.e., 4 d old) stratospheric-intrusion events by STEFLUX suggested that deep events only had a minor influence (up to 1.1% of the period, in August) on deep events during the variability in near-surface summer O-3 at DA. The deep events during the polar night were significantly higher than those during the polar day. This work provides unique data on ozone variation at DA and expands our knowledge of such events in Antarctica. Data are available at https://doi.org/10.5281/zenodo.3923517 (Ding and Tian, 2020).