Polar Ozone Destruction Research Articles

HOCl retrievals from the Atmospheric Chemistry Experiment

HOCl is a chlorine reservoir molecule found in the stratosphere and in the marine boundary layer. In the stratosphere, it originates from anthropogenic emissions of long-lived chlorine-containing molecules as chlorofluorocarbons (CFCs). HOCl is also a key species in polar ozone destruction and the formation of the Antarctic ozone hole. A new HOCl retrieval has been developed using solar occultation spectra recorded by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) from orbit. Altitude-latitude volume mixing ratio (VMR) distributions of HOCl are presented for the entire mission (2004-2020) and for four seasonal quarters. A time series of quarterly averages for the region 60°S-60°N, 35.5-39.5 km altitude shows a marginally significant trend of -0.23±0.11 ppt/year consistent with the success of the Montreal Protocol.

The role of the polar vortex strength during winter in Arctic ozone depletion from late winter to spring

The polar ozone destruction occurs as a result of the chemical processes and catalytic cycles with the participation of polar stratospheric clouds (PSCs) in the presence of weak solar radiation inside the polar vortex from late winter to spring. However, in some years, ozone depletion was not observed under strong polar vortex conditions (in the presence of PSCs). Based on the ERA-Interim reanalysis data and the NASA Goddard Space Flight Center (GSFC) satellite data, we show that the polar vortex strength in early winter plays an important role in polar ozone depletion. If the short-term weakening or splitting of the polar vortex, occurring with PSC melting, happened during the winter, then, in most cases, ozone destruction during the subsequent period from late winter to spring was not observed even under conditions of the strong polar vortex containing PSCs.

Multiple symptoms of total ozone recovery inside the Antarctic vortex during austral spring

Abstract. The long-term evolution of total ozone column inside the Antarctic polar vortex is investigated over the 1980–2017 period. Trend analyses are performed using a multilinear regression (MLR) model based on various proxies for the evaluation of ozone interannual variability (heat flux, quasi-biennial oscillation, solar flux, Antarctic oscillation and aerosols). Annual total ozone column measurements corresponding to the mean monthly values inside the vortex in September and during the period of maximum ozone depletion from 15 September to 15 October are used. Total ozone columns from the Multi-Sensor Reanalysis version 2 (MSR-2) dataset and from a combined record based on TOMS and OMI satellite datasets with gaps filled by MSR-2 (1993–1995) are considered in the study. Ozone trends are computed by a piece-wise trend (PWT) proxy that includes two linear functions before and after the turnaround year in 2001 and a parabolic function to account for the saturation of the polar ozone destruction. In order to evaluate average total ozone within the vortex, two classification methods are used, based on the potential vorticity gradient as a function of equivalent latitude. The first standard one considers this gradient at a single isentropic level (475 or 550 K), while the second one uses a range of isentropic levels between 400 and 600 K. The regression model includes a new proxy (GRAD) linked to the gradient of potential vorticity as a function of equivalent latitude and representing the stability of the vortex during the studied month. The determination coefficient (R2) between observations and modelled values increases by ∼ 0.05 when this proxy is included in the MLR model. Highest R2 (0.92–0.95) and minimum residuals are obtained for the second classification method for both datasets and months. Trends in September over the 2001–2017 period are statistically significant at 2σ level with values ranging between 1.84 ± 1.03 and 2.83 ± 1.48 DU yr−1 depending on the methods and considered proxies. This result confirms the recent studies of Antarctic ozone healing during that month. Trends from 2001 are 2 to 3 times smaller than before the turnaround year, as expected from the response to the slowly ozone-depleting substances decrease in polar regions. For the first time, significant trends are found for the period of maximum ozone depletion. Estimated trends from 2001 for the 15 September–15 October period over 2001–2017 vary from 1.21 ± 0.83 to 1.96 DU ± 0.99 yr−1 and are significant at 2σ level. MLR analysis is also applied to the ozone mass deficit (OMD) metric for both periods, considering a threshold at 220 DU and total ozone columns south of 60∘ S. Significant trend values are observed for all cases and periods. A decrease of OMD of 0.86 ± 0.36 and 0.65 ± 0.33 Mt yr−1 since 2001 is observed in September and 15 September–15 October, respectively. Ozone recovery is also confirmed by a steady decrease of the relative area of total ozone values lower than 175 DU within the vortex in the 15 September–15 October period since 2010 and a delay in the occurrence of ozone levels below 125 DU since 2005.

The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes

The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a "geoengineering" scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO2 would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole.

A revised linear ozone photochemistry parameterization for use in transport and general circulation models: multi-annual simulations

Abstract. This article describes the validation of a linear parameterization of the ozone photochemistry for use in upper tropospheric and stratospheric studies. The present work extends a previously developed scheme by improving the 2-D model used to derive the coefficients of the parameterization. The chemical reaction rates are updated from a compilation that includes recent laboratory work. Furthermore, the polar ozone destruction due to heterogeneous reactions at the surface of the polar stratospheric clouds is taken into account as a function of the stratospheric temperature and the total chlorine content. Two versions of the parameterization are tested. The first one only requires the solution of a continuity equation for the time evolution of the ozone mixing ratio, the second one uses one additional equation for a cold tracer. The parameterization has been introduced into the chemical transport model MOCAGE. The model is integrated with wind and temperature fields from the ECMWF operational analyses over the period 2000–2004. Overall, the results from the two versions show a very good agreement between the modelled ozone distribution and the Total Ozone Mapping Spectrometer (TOMS) satellite data and the "in-situ" vertical soundings. During the course of the integration the model does not show any drift and the biases are generally small, of the order of 10%. The model also reproduces fairly well the polar ozone variability, notably the formation of "ozone holes" in the Southern Hemisphere with amplitudes and a seasonal evolution that follow the dynamics and time evolution of the polar vortex. The introduction of the cold tracer further improves the model simulation by allowing additional ozone destruction inside air masses exported from the high to the mid-latitudes, and by maintaining low ozone content inside the polar vortex of the Southern Hemisphere over longer periods in spring time. It is concluded that for the study of climate scenarios or the assimilation of ozone data, the present parameterization gives a valuable alternative to the introduction of detailed and computationally costly chemical schemes into general circulation models.

Influence of polar ozone loss on northern midlatitude regions estimated by a high‐resolution chemistry transport model during winter 1999/2000

The Modèle Isentropique de transport Mésoéchelle de l'Ozone Stratosphérique par Advection avec CHIMie (MIMOSA‐CHIM) three‐dimensional high‐resolution chemical transport model has been developed to estimate the contribution of polar ozone destruction to the lower stratosphere ozone budget at midlatitudes. The ability of the model to reproduce the evolution of polar and midlatitude ozone during the 1999/2000 winter is first evaluated by comparisons against lidar and sonde measurements. The modeled potential vorticity (PV) fields are also compared with PV fields derived from ECMWF analyses and the chemical fields of the model are compared with the output of a large‐scale chemical transport model in order to highlight the interest of a high‐resolution model for resolving fine‐scale structures such as polar filaments. A PV‐based analysis is performed to estimate the area covered by polar air, vortex, and filaments in the 45°N–55°N latitude band at 475K and their contribution to ozone loss. The polar air contribution was found to represent usually between 20% and 40% of the total ozone loss in this latitude band but can reach 50% during large vortex intrusions. At 475K, the total chemical ozone loss in nonpolar air between 45°N and 55°N increases from 1% in mid‐December to 15% at the end of March. Several chemical ozone tracers are considered to investigate the origin of the ozone loss in nonpolar air. These tracers allow us to quantify the amount of chemical ozone destruction that occurred in the vortex, in the polar filamentary structures, and in the nonpolar air. Until February, the main contributor to the nonpolar ozone loss is in situ destruction at midlatitudes, but the contribution from the ozone destruction in the polar vortex increases steadily during the winter and represents about 50% of the total midlatitude ozone loss in April, after the vortex breakup. The contribution from the ozone destruction within filamentary structures is found to be quasi‐negligible as a result of the limited number of filaments.

Arctic ozone destruction and chemical‐radiative interaction

Three northern hemisphere winter/springs with contrasting thermal and dynamic characteristics were simulated with a mechanistic model of the middle atmosphere incorporating an interactive chemistry scheme. The three seasonal simulations used different planetary‐wave forcings at the lower boundary, and consequently their respective temperature evolutions represented (1) a relatively mild Arctic winter; (2) a winter comparable to the coldest on record; and (3) a winter more persistently cold than any yet observed. The radiative response to the varying degrees of chemical ozone depletion in these winters was investigated by comparing results from runs that included and excluded the heterogeneous reactions on polar stratospheric clouds (PSCs) which initiate the enhanced destruction of polar ozone. Cooling of the lower stratosphere induced by the enhanced ozone loss ranges from virtually zero in the warmest winter to ∼5 K in the coldest. The extent of any self‐perpetuation of the ozone destruction processes via the induced cooling was examined by using the meteorological fields calculated both with and without PSC‐initiated ozone depletion to drive an off‐line chemical transport model. In winters 1 and 2 the longevity of PSCs and enhanced reactive halogen concentrations is increased only marginally by the cooling arising from the ozone loss, and consequently there is little impact on the net ozone destruction. In winter 3, however, the radiative feedback from the ozone loss leads to a marked prolongation of the lifetime of the enhanced reactive halogens and causes a chemically induced diminution of up to ∼20 Dobson units (DU) in the April ozone column compared with the no‐feedback case. Moreover, in winter 3 the cooling caused by PSC‐initiated ozone depletion delays the springtime weakening of the polar vortex and inhibits the replenishment of Arctic ozone, resulting in a ∼25 DU depression of the ozone column in early May that is due mainly to dynamics. These results suggest that chemical‐radiative interaction via PSC processes has had only a small impact on the ozone distribution in recent Arctic winters, but that it has the potential to become more important should an unprecedentedly cold winter occur while atmospheric halogen concentrations remain artificially high.

Some further calculations on the uptake of HC1 by stratospheric sulphate aerosol droplets

The solubility of HC1 in cold H2SO4/H2O solution is central to an assessment of the role of stratospheric aerosol in polar ozone destruction. In the recent past, the increases in stratospheric H2SO4/H2O aerosol caused by the eruption of Mt Pinatubo has led to a number of further assessment studies and it is not yet clear whether the high ClO concentration observed during the winter of 1991/92 are solely due to polar stratospheric clouds, or whether the enhanced liquid aerosol loading is directly responsible for a part of this chlorine activation. The aim of the present paper is to first, obtain a theoretical estimate of the liquid phase diffusion coefficient in liquid H2SO4 and then to re‐evaluate the uptake coefficient of HC1 into supercooled sulphuric acid solution droplets taking into account the dipole moment correction of the gas phase diffusivity of HC1.

Transport, Radiative, and Dynamical Effects of the Antarctic Ozone Hole: A GFDL “SKYHI” Model Experiment

Abstract The GFDL “SKYHI” general circulation model has been used to simulate the effect of the Antarctic “ozone hole” phenomenon on the radiative and dynamical environment of the lower stratosphere. Both the polar ozone destruction and photochemical restoration chemistries are calculated by parameterized simplifications of the still somewhat uncertain chemical processes. The modeled total column ozone depletions are near 25% in spring over Antarctica, with 1% depletion reaching equatorial latitudes by the end of the 4½–year model experiment. In the lower stratosphere, ozone reductions of 5% reach to the equator. Large coolings of about 8 K are simulated in the lower stratosphere over Antarctica in late spring, while a general cooling of about 1–1.5 K is present throughout the Southern Hemisphere lower stratosphere. The model atmosphere experiences a long-term positive temperature-chemical feedback because significant ozone reductions carry over into the next winter. The overall temperature response to th...

HCL solubility and liquid diffusion in aqueous sulfuric acid under stratospheric conditions

The solubility of HCl in cold H2SO4/H2O solutions is central to an assessment of the role of stratospheric aerosol in polar ozone destruction. The interpretation of laboratory measurements of HCl uptake by aqueous H2SO4 requires a knowledge of (1) HCl solubility and (2) the HCl liquid phase diffusion coefficient. Neither quantity is easily determined because of the high H2SO4 concentration and low temperature of the solutions, making experimental data difficult to evaluate and to apply to the real stratospheric situation. To avoid these difficulties, we have used a new thermodynamic model for an improved estimate of HCl solubility, and a viscosity‐based cubic cell model to obtain the diffusion coefficient. The calculated HCl solubility in aqueous H2SO4 below 200 K is up to three orders of magnitude greater than previously thought. This might promote chlorine activation particularly during volcanically perturbed periods with an enhanced stratospheric aerosol loading.

On the formation and sedimentation of stratospheric nitric acid aerosols: Implications for polar ozone destruction

The formation and sedimentation of nitric acid‐aerosols (NA‐aerosols) in the winter polar stratosphere is investigated in the light of recent mass spectrometric in‐situ measurements of gaseous nitric acid performed in the winter arctic stratosphere. We revisit the nitric acid measurements and extend their interpretation by carrying out isentropic trajectory calculations of the airmasses encountered in these experiments and by considering aerosol measurements, which became available recently. Our analysis shows that the mass spectrometer measurements provide strong evidence for nitric acid nucleation and vertical redistribution of nitric acid due to sedimentation of HNO3‐containing aerosols. Both these processes promote halogen‐catalysed destruction of ozone. Moreover, it is concluded that nitric acid nucleation is less efficient than expected from simple equilibrium considerations. Probably, this is due to rapid cooling and inefficient nucleation (inefficient activation of preexisting H2SO4/H2O‐aerosols for HNO3/H2O‐condensation) allowing only a small fraction of the preexisting H2SO4/H2O‐aerosols to serve as active nuclei.

Maximum Supercooling of H2SO4Acid Aerosol Droplets

AbstractHeterogeneous reactions which take place on solid polar stratospheric cloud (PSC) particles and lead to ClOxactivation, have been identified as crucial to polar ozone destruction. Scientific attention is currently focussed on whether similar heterogeneous reactions can also take place on sulfuric acid aerosol droplets. We present theoretical calculations of the homogeneous freezing of sulfuric acid droplets under stratospheric conditions, based on classical theory and using the best available thermodynamical data for the H2SO4–H2O system. For small cooling rates we find that most of the aerosol droplets will freeze as sulfuric acid tetrahydrate (SAT) at about 200 K, whereas for large cooling rates (e. g. in lee waves) large amounts of the aerosol droplets will stay liquid through temperatures as low as 190 K, at which point they freeze as water ice.

Stratospheric nitric acid vapour measurements in the cold Arctic vortex: implications for nitric acid condensation

STRATOSPHERIC nitric acid condensation has recently been proposed1, 2 to take place in the cold winter polar vortex, priming it for chlorine-catalysed ozone destruction. This idea has been developed subsequently3–8. Condensation, thought to proceed via a heterogeneous heteromolecular mechanism involving stratospheric water vapour and pre-existing H2SO4/H2O aerosols, which serve as condensation nuclei, leads to solid nitric acid trihydrate (NAT; HNO3.3H2O) aerosols. It is expected1, 2, 8 that the condensation temperature, Tc(NAT), is significantly greater than that of water-ice, Tc(H2O-ice), given the stratospheric abundances of gaseous nitric acid and water and the thermodynamic properties of stratospheric aerosols8. Knowledge of Tc(NAT) is important because it determines the spatial and temporal extent of NAT aerosols and hence possibly of polar ozone destruction. Here we report in situ measurements of the detailed height distribution of gaseous nitric acid in the cold arctic vortex, using a balloon-borne technique9–16, which offers a much better altitude resolution (30 m) than previous satellite measurements17, 18. Our data set an upper limit to Tc(NAT) of 195 K at 23 km, and are consistent with model predictions based on the present gaseous nitric acid data, typical water vapour abundances and thermodynamic data8 of macroscopic NAT mixtures. However, our upper limit to Tc(NAT) is markedly lower than some of the early model estimates1, 2.