Synoptic-scale drivers of long-term tropospheric ozone variability at Belgrano II station, Antarctica

A 24-year record of ozone and meteorological profiles (1999–2023) from Belgrano II station (77.87° S, 34.62° W), coastal Antarctica, was analysed to investigate the role of synoptic-scale circulation and atmospheric transport in controlling tropospheric ozone variability and long-term change. Air-mass transport pathways were quantified using HYSPLIT trajectory analysis, identifying four airflow regimes: Marine Weddell Sea, Weddell–Antarctic Peninsula, Eastern Coastal Continental and Southern Polar Continental. Tropospheric ozone exhibited a seasonal cycle with a positive vertical gradient, increasing from 12 to 30 ppb at 950 hPa to 45–55 ppb near 300 hPa. Winter maxima (29.1 ± 12.8 ppb at 950 hPa) reflected dynamical accumulation under stable stratification and minimal photochemical loss, whereas summer minima (12.2 ± 6.0 ppb) were driven by photochemical destruction. Ozone was strongly modulated by transport regime: Marine Weddell Sea air masses produced the highest concentrations (29.8 ± 1.2 ppb), consistent with long-range transport from lower latitudes, while Weddell–Antarctic Peninsula flows yielded the lowest (23.5 ± 1.7 ppb), linked to halogen-driven depletion over sea-ice surfaces. Transport-dependent differences of up to 6.3 ppb extended to 400 hPa. Trend analysis revealed positive ozone changes throughout the troposphere, strongest in the boundary layer (1.28 ± 1.84 ppb decade −1 at 915 hPa), accompanied by warming peaking at 1.14 ± 1.39 °C decade −1 at 895 hPa. These coupled trends coincide with intensification of the Amundsen Sea Low and increasing maritime intrusions, reducing katabatic outflow. The results indicate that climate-driven dynamical adjustments are reshaping the chemical structure of the Antarctic troposphere.