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Following the Hunga Tonga–Hunga Ha'apai (HTHH) eruption in January 2022, stratospheric ozone depletion was observed at Southern Hemisphere mid‐latitudes and over Antarctica during the 2022 austral wintertime and springtime, respectively. The eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. This work examines the chemistry contribution of the volcanic materials to ozone depletion using chemistry‐climate model simulations with nudged meteorology. Simulated 2022 ozone and nitrogen oxide (NOx = NO + NO2) anomalies show good agreement with satellite observations. We find that chemistry yields up to 4% ozone destruction at mid‐latitudes near ∼70 hPa in August and up to 20% ozone destruction over Antarctica near ∼80 hPa in October. Most of the ozone depletion is attributed to internal variability and dynamical changes forced by the eruption. Both the modeling and observations show a significant NOx reduction associated with the HTHH aerosol plume, indicating enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol. Plain Language Summary: The January 2022 eruption of the Hunga Tonga‐Hunga Ha'apai underwater volcano injected a large amount of water vapor (H2O) and moderate amounts of sulfur dioxide (SO2) into the stratosphere. Stratospheric ozone depletion was observed following the eruption at Southern Hemisphere (SH) mid‐latitudes and over Antarctica during the 2022 austral wintertime and springtime, respectively. The ozone layer in the stratosphere protects both people and the biosphere by absorbing harmful solar ultraviolet radiation. We use computer simulation to examine the impacts of chemical processes on the ozone layer from the volcanic materials. We find that chemistry results in 4% and 20% of the ozone loss at SH mid‐latitudes near 70 hPa in August and Antarctica around 80 hPa in October respectively. Most of the ozone changes are due to transport and dynamical processes from internal variability in the climate system and a forced response by the HTHH eruption. Key Points: Chemistry yields 4% and 20% ozone depletion in the lower stratosphere at mid‐latitudes and Antarctica in August and October, respectivelyThe majority of ozone depletion is ascribed to internal variability and dynamical changes induced by the eruptionHTHH aerosol plume is associated with notable NOx reduction, indicating enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol [ABSTRACT FROM AUTHOR]

The study aims to estimate and compare the global emission for 20 halocarbons from volcanic and hydrothermal sources into the Earth’s atmosphere. It follows from the results that the contribution of volcanic emission for these species in the depletion of stratospheric ozone in the catalytic halogen cycles does not exceed 0.1%. Still, they significantly impair the level of tropospheric ozone near the volcanoes. The scheme of gas-phase free radical chain halogenation of the hydrocarbons is proposed and confirmed by thermodynamic and kinetic calculations. This explains the experimental ratios between concentrations of CH3I : CH3Br : CH3Cl and CCl4 : CHCl3 : CH2Cl2 : CH3Cl in the volcanic gases. The possible volcanic emission of halocarbons from Erebus and explosive eruptions in the Southern Hemisphere during the Holocene do not have a notable impact on their content in the Antarctic ice. However, volcanic emission of hydrogen halides (HX, X = Cl, Br or I) from powerful eruptions in the Southern Hemisphere during Holocene could deplete the stratospheric ozone substantially, causing a drastic impact of the harmful UV-B radiation on the biota of continents and ocean. We calculated the injected Equivalent Effective Stratospheric Chlorine values and estimated the column ozone percentage change, Δ%O3, for 20 known volcano eruptions in the tropical belt and Southern latitudes. The estimates lead to more than 50% depletion of stratospheric ozone after past powerful volcanic eruptions. The range is estimated for possible ozone depletion after the eruption of Deception Island’s volcano occurred near 4000 BP (from 44 to 56%), which is comparable with those from Krakatoa, Samalas, and Tambora eruptions. A similar analysis was carried out for 192 yrs series of Mt Takahe (West Antarctica) halogen-rich volcanic eruptions at 17,7 kyr, showing extensive stratospheric ozone depletion over Antarctica. Crude estimations of stratospheric ozone depletion (Δ%O3) after Ferrar Large Igneous Province eruptions (183 Ma) in Antarctica were performed, considering the whole LIP volume of basaltic lavas, and they range from 49 to 83%. Given the very low emission rate of HCl due to non-eruptive degassing of the Mt. Erebus volcano, the volcanic emission of Erebus could not be a fundamental reason for modern springtime ozone hole formation over Antarctica.

A large amount of volcanic aerosol is emitted into the stratosphere as a result of large eruptions of tropical volcanoes and contributes to the formation of positive temperature and negative ozone anomalies in the lower tropical stratosphere. Large eruptions with VEI ≥ 5 can cause global ozone depression. A volcanic increase in the temperature of the lower tropical stratosphere increases the stratospheric meridional temperature gradient and thus strengthens the polar vortex. Polar ozone depletion occurs under the conditions of the winter–spring strengthening of the vortex. Stratospheric ozone anomalies due to an increase in the UV-B irradiation can manifest themselves in the degradation of coniferous forests, which serve a biospheric indicator of climate changes. Mass focal drying of dark coniferous forests has been observed in the mountain regions of southern Siberia since the middle 1990s under an increase in the surface UV-B radiation as a result of ozone depletion after the eruption of Mount Pinatubo. [ABSTRACT FROM AUTHOR]

Interpretation of NO3− variability recorded in ice cores remains challenging as it can be lost from snow. Here, we present 60‐year records of NO3− and its isotopic composition (δ15N, δ18O, and Δ17O) in snow in central Antarctica, Dome A. In the upper ∼90 cm snowpack, variations in concentration and isotopic composition of NO3− are dominated by photolytic loss, and δ18O and Δ17O of NO3− are associated with the recycling of NOx to NO3− in the condensed phase driven by photolysis. In the deeper snowpack (∼1960–2000), we observe prolonged trends in concentration and isotopic composition of NO3−, which are best explained as enhanced snow NO3− photolysis due to long‐term decreasing total column ozone (TCO). That is, the prolonged period of trends in NO3− and its isotopes in extremely low snow accumulation sites such as Dome A relay information on variations in TCO and consequently surface solar ultraviolet radiation over time. Plain Language Summary: The atmospheric information contained in polar snow/ice nitrate (NO3−) is of great interest in paleoclimate research. The interpretation of NO3− variability recorded in ice cores, however, remains challenging as atmospheric NO3− can be lost from snow prior to ice formation. Here, we present 60‐year records of NO3− and its isotopic composition in snow pits collected from Dome A, an exceptionally low snow accumulation site in central Antarctica. Analysis of our data shows that variations in concentration and isotopic composition of NO3− in the upper snowpack are dominated by photolytic loss, resulting in distinct trends in nitrogen and oxygen isotopes of NO3−. In the deeper snowpack, we observe clear trends in both concentration and isotopic composition of NO3−, which are closely associated with enhanced snow NO3− UV photolysis due to the decreasing stratospheric ozone during ∼1960–2000. That is, elevated UV doses reaching the snow surface as a result of larger Antarctic ozone holes significantly promoted snow NO3− photolysis. These findings raise the prospect of better understanding of past stratospheric ozone variations using ice core NO3− isotope records. Key Points: Condensed phase NO3− reformation in snow driven by photolysis is recorded in δ18O and Δ17OClear trends in NO3− and its isotopes from ∼1960 to 2000 were related to depletion of stratospheric ozoneInterannual variations in snow NO3− were dominated by local physical processes and snow chemistry [ABSTRACT FROM AUTHOR]

In the winter and spring of 2019/2020, the unusually cold, strong, and stable polar vortex created favorable conditions for ozone depletion in the Arctic. Chemical ozone loss started earlier than in any previous year in the satellite era and continued until late March, resulting in the unprecedented reduction of the ozone column. The vortex was located above the Polar Environment Atmospheric Research Laboratory in Eureka, Canada (80°N, 86°W) from late February to the end of April, presenting an excellent opportunity to examine ozone loss from a single ground station. Measurements from a suite of instruments show that total column ozone was at an all‐time low in the 20‐year data set, 22–102 DU below previous records set in 2011. Ozone minima (<200 DU), enhanced OClO and BrO slant columns, and unusually low‐HCl, ClONO2, and HNO3 columns were observed in March. Polar stratospheric clouds were present as late as 20 March, and ozonesondes show unprecedented depletion in the March and April profiles (to <0.2 ppmv). While both chemical and dynamical factors lead to reduced ozone when the vortex is cold, the contribution of chemical depletion (based on the variable correlation of ozone and temperature) was exceptional in spring 2020 when compared to typical Arctic winters. Mean chemical ozone loss over Eureka was estimated to be 111–126 DU (27%–31%) using April measurements and passive ozone from the SLIMCAT chemical transport model. While absolute ozone loss was generally smaller in 2020 than in 2011, percentage ozone loss was greater in 2020. Plain Language Summary: While an ozone hole forms over Antarctica every year, the Arctic typically does not experience such dramatic ozone loss. The chlorine and bromine (halogen) reactions that destroy ozone require very low temperatures that are rarely observed in the Arctic stratosphere. The winter and spring of 2019/2020, however, was unusually cold in the Arctic, and consequently, a large amount of ozone was destroyed by halogen chemistry. To understand the behavior of ozone in spring 2020, we use measurements from the Polar Environment Atmospheric Research Laboratory in Eureka, Canada. Eureka (at 80°N) is one of the northernmost research stations in the world, and thus an ideal location to observe ozone loss. Spring 2020 ozone minima were lower than any in the 20‐year data set, and ozone destruction was ongoing until the end of March, which is rare in the Arctic. While ozone concentrations are largely determined by circulation patterns in the Arctic stratosphere, chemistry in spring 2020 was a much larger factor than usual. Halogen chemistry destroyed 27%–31% of the total ozone, compared to about 10% in a typical winter. The only year on record with comparable ozone loss is 2011, and a larger percentage of the ozone column was lost in 2020. Key Points: Record low ozone columns (<200 DU) were observed over Eureka in spring 2020Limited dynamical resupply of ozone and chemical destruction both contributed to reduced ozone columnsMean chemical ozone loss of 111–126 DU (27%–31%) represents similar absolute loss and greater relative loss compared to that in spring 2011 [ABSTRACT FROM AUTHOR]

We here reflect on two important articles on stratospheric ozone depletion written by P. J. Crutzen (1974) and P. J. Crutzen and D. H. Ehhalt (1977) in the early 1970s. These articles provide a clear description of the stratosphere and the most important chemical reactions involved in stratospheric ozone depletion. They present modeling results and provide recommendations for future research on stratospheric ozone depletion caused by chloro-fluoro-carbons, supersonic transport, nitrous oxide, and nuclear explosions. These two articles represent the beginning of a scientific era, which led to discovery of the Antarctic ozone hole and political action in the form of the Montreal Protocol and its amendments. [ABSTRACT FROM AUTHOR]

Abstract: The relative impacts of greenhouse gas (GHG) increase and stratospheric ozone depletion on stratospheric mean age of air in the 1960–2010 period are quantified using the Goddard Earth Observing System Chemistry‐Climate Model. The experiment compares controlled simulations using a coupled atmosphere‐ocean version of the Goddard Earth Observing System Chemistry‐Climate Model, in which either GHGs or ozone depleting substances, or both factors evolve over time. The model results show that GHGs and ozone depleting substances have about equal contributions to the simulated mean age decrease, but GHG increases account for about two thirds of the enhanced strength of the lower stratospheric residual circulation. It is also found that both the acceleration of the diabatic circulation and the decrease of the mean age difference between downwelling and upwelling regions are mainly caused by GHG forcing. The results show that ozone depletion causes an increase in the mean age of air in the Antarctic summer lower stratosphere through two processes: (1) a seasonal delay in the Antarctic polar vortex breakup that inhibits young midlatitude air from mixing with the older air inside the vortex, and (2) enhanced Antarctic downwelling that brings older air from middle and upper stratosphere into the lower stratosphere. [ABSTRACT FROM AUTHOR]

The Montreal Protocol has set an extraordinary example by applying scientific discoveries, technological innovations, and swift political actions to solving one of the most urgent environmental problems facing humans. With its ongoing implementation, the stratospheric ozone is expected to return to its 1980 levels around mid-twenty-first century. In addition, the Montreal Protocol has contributed to mitigating climate change by reducing the emissions of certain greenhouse gases. The management of several short-lived climate forcers, including hydrofluorocarbons, tropospheric ozone, black carbon, and methane, is worthy of consideration as a fast-response, near-term measure to curb climate change, while international treaties to reduce the emissions of long-lived climate forcers, such as carbon dioxide, are under discussion. This paper aims to provide a concise overview of the scientific concepts and atmospheric processes behind these policy considerations. The focus is on the fundamental atmospheric chemistry that provides the basis for a co-benefits approach in mitigating both climate change and stratospheric ozone depletion. [ABSTRACT FROM AUTHOR]