On Recent Large Antarctic Ozone Holes and Ozone Recovery Metrics.

The 2015 and 2020 ozone holes set record sizes in October–December. We show that these years, as well as other recent large ozone holes, still adhere to a fundamental recovery metric: the later onset of early spring ozone depletion as chlorine and bromine diminishes. This behavior is also captured in the Whole Atmosphere Chemistry Climate Model. We quantify observed recovery trends of the onset of the ozone hole and in the size of the September ozone hole, with good model agreement. A substantial reduction in ozone hole depth during September over the past decade is also seen. Our results indicate that, due to dynamical phenomena, it is likely that large ozone holes will continue to occur intermittently in October–December, but ozone recovery will still be detectable through the later onset, smaller, and less deep September ozone holes: metrics that are governed more by chemical processes. Plain Language Summary: The ozone hole that forms every spring in the Southern Hemisphere over Antarctica is expected to recover within the next 50 years. However, there have been several large ozone holes recently. In 2015, a record large volcanic eruption injected a large amount of sulfur into the upper atmosphere, which helps deplete ozone. In 2020, the Australian bushfires also injected a large amount of aerosol into the upper atmosphere, with a possible similar consequence. In this study, we show that by investigating a key time period in the early spring when the ozone hole is forming, the dynamical influence and the influence of volcanic and bushfire aerosols on ozone depletion over Antarctica is not as important and therefore ozone recovery can still be detected. Key Points: The seasonal onset of ozone depletion continues to slow down due to decreasing stratospheric chlorine and bromine concentrationsRecent large ozone holes of 2015, 2018, 2020, and 2021 display slower seasonal onset compared to 1999–2008 despite record sizes laterSeptember ozone hole size trends over 2000–2021 at different depth thresholds (such as 220, 175, 130 DU) indicate recovery [ABSTRACT FROM AUTHOR]