Ozone Loss Research Articles

Cosmic ray–driven electron-induced reaction theory quantifies spatiotemporal variations in lower-stratospheric ozone and temperature

Cosmic rays (CRs) play an important role in affecting planetary and interstellar climate and environment. Here, we apply the CR-driven electron-induced reaction (CRE) theory of ozone depletion to obtain a quantitative understanding of spatiotemporal variations in Earth's lower-stratospheric ozone (LSO) and temperature, which provide fingerprints for the mechanisms of ozone depletion and examine the impact of nonhalogen greenhouse gases on the ozone layer. We first show from observations that both LSO and temperature display pronounced 11-y cyclic variations over Antarctica and mid-latitudes, while weak (no apparent) cyclic variations over the tropics. These observations are consistent with the prediction by the CRE theory. Second, our no-parameter CRE theoretical calculations give the vertical profile of ozone loss in perfect agreement with observations at the Antarctic Syowa station and reproduce well the time-series variations of both LSO and temperature in the polar, mid-latitude, and tropical regions, including the previously reported large ozone depletion in the lower stratosphere over the tropics. The results also demonstrate that both LSO and temperature are controlled by CRs and ozone-depleting substances (ODSs) only. Moreover, CRE calculations exhibit complex phenomena in future trends of LSO and temperature, which are strongly affected by the future trend of CR fluxes. The latter might even lead to almost no recovery of the ozone hole over Antarctica and no returning to the 1980 level over the tropics by 2100. This study greatly improves quantitative understanding of ozone depletion and climate in the global lower stratosphere and offers predictions on future trends.

Evaluation of processes driving iodine monoxide and ozone variability over the Western Pacific warm pool

Iodine chemistry exerts a nonnegligible influence on tropospheric ozone depletion over oceanic regions. The impact of iodine has been extensively studied using three-dimensional chemical transport models (CTMs). However, the factors governing the variability of iodine monoxide (IO) and ozone in the marine boundary layer (MBL) remain uncertain. This study examines the impact of fine-scale meteorological variability and ozone-independent iodine sources on the MBL IO and ozone concentrations over the Western Pacific Warm Pool (WPWP) through ship-borne observations and high-resolution CTMs during November–December 2014. The high (0.56∘)-resolution model demonstrates a negative correlation between IO and ozone at the observation locations (r=-0.45), which is more closely aligned with that derived from the ship-borne observation data (r=-0.70) than the coarse (2.8∘)-resolution model (r=0.08). Sensitivity analysis indicates that a contrast in the correlation between the 0.56∘ and 2.8∘ resolutions emerges from the interplay of fine-scale atmospheric transport and chemistry processes, rather than from fine-scale atmospheric transport solely or ozone-dependent oceanic iodine release. This interplay leads to a greater ozone loss mediated by the iodine cycle at 0.56∘ resolution (by 0.56 ppbv day-1) compared to that at 2.8∘ resolution (by 0.20 ppbv day-1), due to the reduced mixing with air outside the MBL over the WPWP at finer resolution. Furthermore, incorporating ozone-independent iodine sources such as photolysis of CH2I2, CH2IBr, and CH2ICl enhances the IO-ozone anti-correlation coefficient (−0.50). These findings highlight the critical roles of interplay of the fine-scale atmospheric transport and chemistry processes and oceanic ozone-independent iodine sources in the co-variability of IO and ozone over the WPWP.

WACCM Simulation of Polar Ozone Response to Relativistic Electron Precipitation

Abstract Various studies have been dedicated to quantifying the atmospheric chemical effects of energetic electron precipitation (EEP), but the contribution from relativistic electron precipitation (REP) was largely overlooked. Based on the precipitating fluxes estimated from Polar‐orbiting Observational Environmental Satellites, we quantify the REP‐induced atmospheric chemical effects using the Whole Atmosphere Community Climate Model. Present results show that direct stratospheric ionization caused by REP can enhance the NOx concentration by a factor of ∼2.58 at ∼37 km altitude, and the HOx concentration by a factor of ∼6.41 at ∼44 km altitude. As for the annual variation, REP causes an additional ozone loss of ∼16.2%–17.1% at ∼30–35 km altitude during winter. Moreover, REP's impact is not confined to winter since the resultant NOx and HOx production occurs in situ. Therefore, neglecting REP would significantly underestimate EEP's total effects on the stratospheric ozone.

The Yield of Oxygenated VOCs from Ozone Deposition on Aged Indoor Surfaces.

Ozone (O3) loss on surfaces forms oxygenated VOCs (OVOCs) that can cause adverse health effects. Previous studies have focused on surface ozonolysis of pure unsaturated compounds on impermeable surfaces, whereas other work has addressed this chemistry in genuine indoor environments. Our goal is to bridge this gap by examining O3 loss and OVOC production on glass and paint in both laboratory experiments, using surfaces purposefully contaminated with pure compounds (squalene, triolein), complex oils (skin, olive), and surfaces that were aged in an occupied apartment. Paint was chosen as a permeable and reactive material, which is the most common indoor surface. It was found that paint aged indoors had lower OVOC yields than glass when exposed to O3, probably because O3 reacts with paint materials rather than with deposited organics. Many OVOCs were measured, including common skin oil ozonolysis products such as acetone, 6-MHO, and 4-OPA; however, the OVOCs with the highest yields from the apartment samples were nonanal and hexanal, with the OVOC levels highly correlated with the amount of cooking that occurred. Experiments using pure compounds and complex oils produce OVOC species similar to those observed on surfaces aged in the apartment.

The January 2022 Hunga eruption cooled the southern hemisphere in 2022 and 2023

The 2022 Hunga volcanic eruption injected a significant quantity of water vapor into the stratosphere while releasing only limited sulfur dioxide. It has been proposed that this excess water vapor could have contributed to global warming, potentially pushing temperatures beyond the 1.5 °C threshold of the Paris Climate Accord. However, given the cooling effects of sulfate aerosols and the contrasting impacts of ozone loss (cooling) versus gain (warming), assessing the eruption’s net radiative effect is essential. Here, we quantify the Hunga-induced perturbations in stratospheric water vapor, sulfate aerosols, and ozone using satellite observations and radiative transfer simulations. Our analysis shows that these components induce clear-sky instantaneous net radiative energy losses at both the top of the atmosphere and near the tropopause. In 2022, the Southern Hemisphere experienced a radiative forcing of −0.55 ± 0.05 W m⁻² at the top of the atmosphere and −0.52 ± 0.05 W m⁻² near the tropopause. By 2023, these values decreased to −0.26 ± 0.04 W m⁻² and −0.25 ± 0.04 W m⁻², respectively. Employing a two-layer energy balance model, we estimate that these losses resulted in cooling of about −0.10 ± 0.02 K in the Southern Hemisphere by the end of 2022 and 2023. Thus, we conclude that the Hunga eruption cooled rather than warmed the Southern Hemisphere during this period.

Assessing Sustainable Eco-Friendly Refrigerants: An EDAS Methodology Approach

Environmental concerns have made looking for eco-friendly refrigerants essential in recent years. Natural refrigerants including ammonium (R717), carbon dioxide (R744), & hydrocarbons (R290 and R600a) are some of the most promising alternatives. Compared to synthetic alternatives. Natural refrigerants are the best option for many cooling applications because of their excellent thermodynamic characteristics and energy efficiency. The usage of these environmentally friendly refrigerants will support sustainable refrigeration practises and help to lower greenhouse gas emissions. The search for environmentally friendly refrigerators has drawn a lot of attention recently as environmental concerns have increased. The investigation of alternate alternatives has been motivated by concerns over the negative impact of conventional chemical the refrigerants on the loss of ozone and global warming. Natural refrigerants, which provide a sustainable and environmentally benign alternative to cooling applications, are among the most promising choices. such as ammonia (R717), carbon monoxide (R744), and hydrocarbon (R290 and R600a), have emerged as the best options. for artificial substitutes. This introduction lays the groundwork for further investigation into the characteristics and advantages of these environmentally benign refrigerants. Investigating more suitable eco-friendly refrigerants is crucial for tackling the urgent environmental issues connected to conventional synthetic refrigerants. These refrigerants are problematic in the long run since they contribute to the destruction of the ozone barrier and the acceleration of global warming. Through the identification and promotion of natural refrigerants including ammonia (R717), oxygen (R744), and oils (R290 and R600a), the research seeks to create environmentally friendly alternatives. By using these green refrigerants in cooling systems, greenhouse gas emissions can be significantly reduced, which will help slow the effects of climate change. Additionally, by advancing environmentally conscious and energy-efficient refrigeration technology, our research promotes a more sustainable and greener future. A multi-objective optimisation strategy used to resolve choice issues is called EDAS, which It entails assessing prospective solutions according to how far they are from the Pareto front's average answer, which captures trade-offs between competing goals. By considering both the diversity of the solutions and their proximity to the mean, EDAS seeks to identify the most desirable options. The EDAS methodology assists decision-makers in finding the best solutions that balance various goals by combining these elements. In several disciplines, including engineering, finance, and environmental management, this strategy has been employed with success. Alternative parameters taken as r134a, r152a, r1234yf, r1234ze (E), r1233zd (E), r290, r600a, r744. Evaluation parameters taken as Critical Temperature, Vapor density, Latent heat of vaporization, Critical Pressure, Saturated pressure, Liquid density, Viscosity of liquid. r134a in 6th rank. r152a in 5th rank. r1234yf in 7th rank. r1234ze (E) in 4th rank. r1233zd (E) in 3rd rank. r290 in 2nd rank. r600a in 1st rank. r744 in 8th rank. Best sustainable eco-friendly refrigerants are compared and given rank. According to the characteristics. r134a in 6th rank. r152a in 5th rank. r1234yf in 7th rank. r1234ze (E) in 4th rank. r1233zd (E) in 3rd rank. r290 in 2nd rank. r600a in 1st rank. r744 in 8th rank.

Polar mesospheric ozone loss initiates downward coupling of solar signal in the Northern Hemisphere

Solar driven energetic particle precipitation (EPP) is an important factor in polar atmospheric ozone balance and has been linked to ground-level regional climate variability. However, the linking mechanism has remained ambiguous. The observed and simulated ground-level changes start well before the processes from the main candidate, the so-called EPP-indirect effect, would start. Here we show that initial reduction of polar mesospheric ozone and the resulting change in atmospheric heating rapidly couples to dynamics, transferring the signal downwards, shifting the tropospheric jet polewards. This pathway is not constrained to the polar vortex. Rather, a subtropical route initiated by a changing wind shear plays a key role. Our results show that the signal propagates downwards in timescales consistent with observed tropospheric level climatic changes linked to EPP. This pathway, from mesospheric ozone to regional climate, is independent of the EPP-indirect effect, and solves the long-standing mechanism problem for EPP effects on climate.

Near-future rocket launches could slow ozone recovery

Rocket emissions thin the stratospheric ozone layer. To understand if significant ozone losses could occur as the launch industry grows, we examine two scenarios. Our ‘ambitious’ scenario (2040 launches/year) yields a −0.29% depletion in annual-mean, near-global total column ozone in 2030. Antarctic springtime ozone decreases by 3.9%. Our ‘conservative’ scenario (884 launches/year) yields −0.17% annual, near-global depletion; current licensing rates suggest this scenario may be exceeded before 2030. Ozone losses are driven by the chlorine produced from solid rocket motor propellant, and black carbon which is emitted from most propellants. The ozone layer is slowly healing from the effects of CFCs, yet global-mean ozone abundances are still 2% lower than measured prior to the onset of CFC-induced ozone depletion. Our results demonstrate that ongoing and frequent rocket launches could delay ozone recovery. Action is needed now to ensure that future growth of the launch industry and ozone protection are mutually sustainable.

The impact of dehydration and extremely low HCl values in the Antarctic stratospheric vortex in mid-winter on ozone loss in spring

Abstract. Simulations of Antarctic chlorine and ozone chemistry in previous work show that in the core of the Antarctic vortex (16–18 km, 85–55 hPa, 390–430 K) HCl null cycles (initiated by reactions of Cl with CH4 and CH2O) are effective. These HCl null cycles cause both HCl molar mixing ratios to remain very low throughout Antarctic winter and spring. They cause ozone-destroying chlorine (ClOx) to remain enhanced so that rapid ozone depletion proceeds. Here we investigate the impact of the observed dehydration in Antarctica, which strongly reduces ice formation and the uptake of HNO3 from the gas phase; however the efficacy of HCl null cycles is not affected. Moreover, also when using the observed very low HCl molar mixing ratios in Antarctic winter as an initial value, HCl null cycles are efficient in maintaining low HCl (and high ClOx) throughout winter and spring. Further, the reaction CH3O2+ClO is important for the efficacy of the HCl null cycle initiated by the reaction CH4+Cl. Using the current kinetic recommendations instead of earlier ones has very little impact on the simulations. All simulations presented here for the core of the Antarctic vortex show extremely low minimum ozone values (below 50 ppb) in late September to early October in agreement with observations.

Long‐Term Temperature Impacts of the Hunga Volcanic Eruption in the Stratosphere and Above

Abstract Global average upper atmosphere temperature changes linked with the Hunga volcanic eruption (January 2022) are analyzed based on satellite measurements and compared with chemistry‐climate model simulations. Results show stratospheric cooling of −0.5 to −1.0 K in the middle and upper stratosphere during 2022 through middle 2023, followed by stronger cooling (−1.0 to −2.0 K) in the mesosphere after middle 2023. The cooling patterns follow the upward propagating water vapor (H2O) anomalies from Hunga, and similar behavior is found between observations and model simulations. While the stratospheric cooling is mainly due to radiative cooling from enhanced H2O, the mesospheric temperature changes result from ozone losses in the mesosphere, which are in‐turn driven by HOx radicals from Hunga H2O. Comparisons with the multi‐decade climate record show that Hunga impacts on stratospheric temperatures have similar magnitude, but opposite sign, to temperature effects from the large El Chichón (1982) and Pinatubo (1991) volcanic eruptions.

Arctic halogens reduce ozone in the northern mid-latitudes

While the dominant role of halogens in Arctic ozone loss during spring has been widely studied in the last decades, the impact of sea-ice halogens on surface ozone abundance over the northern hemisphere (NH) mid-latitudes remains unquantified. Here, we use a state-of-the-art global chemistry-climate model including polar halogens (Cl, Br, and I), which reproduces Arctic ozone seasonality, to show that Arctic sea-ice halogens reduce surface ozone in the NH mid-latitudes (47°N to 60°N) by ~11% during spring. This background ozone reduction follows the southward export of ozone-poor and halogen-rich air masses from the Arctic through polar front intrusions toward lower latitudes, reducing the springtime tropospheric ozone column within the NH mid-latitudes by ~4%. Our results also show that the present-day influence of Arctic halogens on surface ozone destruction is comparatively smaller than in preindustrial times driven by changes in the chemical interplay between anthropogenic pollution and natural halogens. We conclude that the impact of Arctic sea-ice halogens on NH mid-latitude ozone abundance should be incorporated into global models to improve the representation of ozone seasonality.

Impacts of hydrogen on tropospheric ozone and methane and their modulation by atmospheric NOx

Atmospheric hydrogen concentrations have been increasing in recent decades. Hydrogen is radiatively inert, but it is chemically reactive and exerts an indirect radiative forcing through chemistry that perturbs the concentrations of key species within the troposphere, including ozone. Using the atmospheric version of the United Kingdom Earth System Model, we analyse the impact of 10% increased surface concentrations of hydrogen on ozone production and loss. We also analyse the impact of this hydrogen in atmospheres with lower anthropogenic emissions of nitrogen oxides (80% and 30% of present-day anthropogenic surface emissions), as this is a likely outcome of the transition from fossil fuels towards cleaner technologies. In each case, we also assess the changes in hydroxyl radical concentration and hence methane lifetime and calculate the net impact on the hydrogen tropospheric global warming potential (GWP). We find that the hydrogen tropospheric GWP100 will change relatively little with decreases in surface anthropogenic NOx emissions (9.4 and 9.1 for our present day and 30% anthropogenic emissions, respectively). The current estimate for hydrogen GWP100 can therefore be applied to future scenarios of differing NOx, although this conclusion may be impacted by future changes in emissions of other reactive species.

Elevated Tropospheric Iodine Over the Central Continental United States: Is Iodine a Major Oxidant of Atmospheric Mercury?

Abstract Previous efforts to measure atmospheric iodine have focused on marine and coastal regions. We report the first ground‐based tropospheric iodine monoxide (IO) radical observations over the central continental United States. Throughout April 2022, IO columns above Storm Peak Laboratory, Colorado (3,220 m.a.s.l.) ranged from 0.7 ± 0.5 to 3.6 ± 0.5 × 1012 (average: 1.9 × 1012 molec cm−2). IO was consistently elevated in air masses transported from over the Pacific Ocean. The observed IO columns were up to three times higher and the range was larger than predicted by a global model, which warrants further investigation into iodine sources, sinks, ozone loss, and particle formation. IO mixing ratios increased with altitude. At the observed levels, iodine may be competitive with bromine as an oxidant of elemental mercury at cold temperatures typical of the free troposphere. Iodine‐induced mercury oxidation is missing in atmospheric models, understudied, and helps explain model underestimation of oxidized mercury measurements.

The Influence of Stratospheric Hydration From the Hunga Eruption on Chemical Processing in the 2023 Antarctic Vortex

Abstract We use measurements of trace gases from the Microwave Limb Sounder and polar stratospheric clouds (PSCs) from the Cloud‐Aerosol Lidar with Orthogonal Polarization to investigate how the extraordinary stratospheric water vapor enhancement from the 2022 Hunga eruption affected polar processing during the 2023 Antarctic winter. Although the dynamical characteristics of the vortex itself were generally unexceptional, the excess moisture initially raised PSC formation threshold temperatures above typical values. Cold conditions, especially in early July, prompted ice PSC formation and unusually severe irreversible dehydration at higher levels (500–700 K), while atypical hydration occurred at lower levels (380–460 K). Heterogeneous chemical processing was more extensive, both vertically (up to 750–800 K) and temporally (earlier in the season), than in prior Antarctic winters. The resultant HCl depletion and ClO enhancement redefined their previously observed ranges at and above 600 K. Albeit unmatched in the satellite record, the early‐winter upper‐level chlorine activation was insufficient to induce substantial ozone loss. Chlorine activation, denitrification, and dehydration processes ran to completion by July/August, with trace gas evolution mostly following the climatological mean thereafter, but with chlorine deactivation starting slightly later than usual. While cumulative ozone losses at 410–550 K were relatively large, probably because of the delayed chlorine deactivation, they were not unprecedented. Thus, ozone depletion was unremarkable throughout the lower stratosphere. Although Hunga enhanced PSC formation and chemical processing in early winter, saturation of lower stratospheric denitrification, dehydration, and chlorine activation (as is typical in the Antarctic) prevented an exceptionally severe ozone hole in 2023.

Mesospheric Ozone Depletion during 2004–2024 as a Function of Solar Proton Events Intensity

Solar proton events (SPEs) affect the Earth’s atmosphere, causing additional ionization in the high-latitude mesosphere and stratosphere. Ionization rates from such solar proton events maximize in the stratosphere, but the formation of ozone-depleting nitrogen and hydrogen oxides begins at mesospheric altitudes. The destruction of mesospheric ozone is associated with protons with energies of about 10 MeV and higher and will strongly depend on the intensity of the flux of these particles. Most studies investigating the impact of SPEs on the characteristics of the middle atmosphere have been based on either simulations or reanalysis datasets, and some studies have used satellite observations to validate model results. We study the impact of SPEs on cold-season ozone loss in both the northern and southern hemispheres using Aura MLS mesospheric ozone measurements over the 2004 to 2024 period. Here, we show how strongly SPEs can deplete polar mesospheric ozone in different hemispheres and attempt to evaluate this dependence on the intensity of solar proton events. We found that moderate SPEs consisting of protons with an energy of more than 10 MeV and a flux intensity of more than 100 pfu destroy mesospheric ozone in the northern hemisphere up to 47% and in the southern hemisphere up to 33%. For both hemispheres, the peak of winter ozone loss was observed at about 76 km. In the northern hemisphere, maximum winter ozone loss was observed on the second day after a solar proton event, but in the southern hemisphere, winter ozone depletion was already detected on the first day. In the southern hemisphere, mesospheric ozone concentrations return to pre-event levels on the ninth day after a solar proton event, but in the northern hemisphere, even on the tenth day after a solar proton event, the mesospheric ozone layer may not be fully recovered. The strong SPEs with a proton flux intensity of more than 1000 pfu lead to a maximum winter ozone loss of up to 85% in the northern hemisphere, and in the southern hemisphere winter, ozone loss reaches 73%.

Ozone Loss on Painted Surfaces: Dependence on Relative Humidity, Aging, and Exposure to Reactive SVOCs.

Ozone and its oxidation products result in negative health effects when inhaled. Despite painted surfaces being the most abundant surface in indoor spaces, surface loss remains one of the largest uncertainties in the indoor ozone budget. Here, ozone uptake coefficients (γO3) on painted surfaces were measured in a flow-through reactor where 79% of the inner surfaces were removable painted glass sheets. Flat white paint initially had a high uptake coefficient (8.3 × 10-6) at 20% RH which plateaued to 1.1 × 10-6 as the paint aged in an indoor office over weeks. Increasing the RH from 0 to 75% increased γO3 by a factor of 3.0, and exposure to 134 ppb of α-terpineol for 1 h increased γO3 by a factor of 1.6 at 20% RH. RH also increases α-terpineol partitioning to paint, further increasing ozone loss, but the type of paint (flat, eggshell, satin, semigloss) had no significant effect. A kinetic multilayer model captures the dependence of γO3 on RH and the presence of α-terpineol, indicating the reacto-diffusive depth for O3 is 1 to 2 μm. Given the similarity of the kinetics on aged surfaces across many paint types and the sustained reactivity during aging, these results suggest a mechanism for catalytic loss.

Technical note: An assessment of the performance of statistical bias correction techniques for global chemistry–climate model surface ozone fields

Abstract. State-of-the-art chemistry–climate models (CCMs) still show biases compared to ground-level ozone observations, illustrating the difficulties and challenges remaining in the simulation of atmospheric processes governing ozone production and loss. Therefore, CCM output is frequently bias-corrected in studies seeking to explore the health or environmental impacts from changing air quality burdens. Here, we assess four statistical bias correction techniques of varying complexities and their application to surface ozone fields simulated with four CCMs and evaluate their performance against gridded observations in the EU and US. We focus on two time periods (2005–2009 and 2010–2014), where the first period is used for development and training and the second to evaluate the performance of techniques when applied to model projections. We find that all methods are capable of significantly reducing the model bias. However, biases are lowest when we apply more complex approaches such as quantile mapping and delta functions. We also highlight the sensitivity of the correction techniques to individual CCM skill at reproducing the observed distributional change in surface ozone. Ensemble simulations available for one CCM indicate that model ozone biases are likely more sensitive to the process representation embedded in chemical mechanisms than to meteorology.

Three‐Dimensional Modeling of the O2(1∆) Dayglow: Dependence on Ozone and Temperatures

Abstract Future space missions dedicated to measuring CO2 on a global scale can make advantageous use of the O2 band at 1.27 μm to retrieve the air column. The 1.27 μm band is close to the CO2 absorption bands at 1.6 and 2.0 μm, which allows a better transfer of the aerosol properties than with the usual O2 band at 0.76 μm. However, the 1.27 μm band is polluted by the spontaneous dayglow of the excited state O2 (1∆), which must be removed from the observed signal. We investigate here our quantitative understanding of the O2(1∆) dayglow with a chemistry‐transport model. We show that the previously reported −13% deficit in O2(1∆) dayglow calculated with the same model is essentially due a −20% to −30% ozone deficit between 45 and 60 km. We find that this ozone deficit is due to excessively high temperatures (+15 K) of the meteorological analyses used to drive the model in the mesosphere. The use of lower analyzed temperatures (ERA5), in better agreement with the observations, slows down the hydrogen‐catalyzed and Chapman ozone loss cycles. This effect leads to an almost total elimination of the ozone and O2(1∆) deficits in the lower mesosphere. Once integrated vertically to simulate a nadir measurement, the deficit in modeled O2(1∆) brightness is reduced to −4.2 ± 2.8%. This illustrates the need for accurate mesospheric temperatures for a priori estimations of the O2(1∆) brightness in algorithms using the 1.27 μm band.

Chemical ozone loss and chlorine activation in the Antarctic winters of 2013–2020

Abstract. The annual formation of an ozone hole in the austral spring has regional and global climate implications. The Antarctic ozone hole has already changed the precipitation, temperature and atmospheric circulation patterns, and thus the surface climate of many regions in the Southern Hemisphere (SH). Therefore, the study of ozone loss variability is important to assess its consequential effects on the climate and public health. Our study uses satellite observations from the Microwave Limb Sounder on Aura and the passive-tracer method to quantify the ozone loss for the past 8 years (2013–2020) in the Antarctic. We observe the highest ozone loss (about 3.5 ppmv) in 2020, owing to the high chlorine activation (about 2.2 ppbv), steady polar vortex, and huge expanses of polar stratospheric clouds (PSCs) (12.6×106 km2) in the winter. The spring of 2019 also showed a high ozone loss, although the year had a rare minor warming in mid-September. The chlorine activation in 2015 (1.9 ppbv) was the weakest, and the wave forcing from the lower latitudes was very high in 2017 (up to −60 km s−1). The analysis shows significant interannual variability in the Antarctic ozone as compared to the immediate previous decade (2000–2010). The study helps to understand the role of dynamics and chemistry in the interannual variability of ozone depletion over the years.

The Chemical Effect of Increased Water Vapor From the Hunga Tonga‐Hunga Ha'apai Eruption on the Antarctic Ozone Hole

Abstract The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. The amount of water vapor injected into the stratosphere was unprecedented in the observational record, increasing the stratospheric water vapor burden by about 10%. Using model runs from the ATLAS chemistry and transport model and Microwave Limb Sounder (MLS) satellite observations, we show that while 20%–40% more water vapor than usual was entrained into the Antarctic polar vortex in 2023 as it formed, the direct chemical effect of the increased water vapor on Antarctic ozone depletion in June through October was minor (less than 4 DU). This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor to the saturation pressure and thus reset any anomalies through the process of dehydration before they can affect ozone loss.