Surface Of Polar Stratospheric Clouds Research Articles

Numerical Modeling of Ozone Loss in the Exceptional Arctic Stratosphere Winter–Spring of 2020

Dynamical processes and changes in the ozone layer in the Arctic stratosphere during the winter of 2019–2020 were analyzed using numerical experiments with a chemistry-transport model (CTM) and reanalysis data. The results of numerical calculations using CTM with Dynamic parameters specified from the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis data, carried out according to several scenarios of accounting for the chemical destruction of ozone, demonstrated that both Dynamic and chemical processes contribute significantly to ozone changes over the selected World Ozone and Ultraviolet Radiation Data Centre network stations, both in the Eastern and in the Western hemispheres. Based on numerical experiments with the CTM, the specific Dynamic conditions of winter–spring 2019–2020 described a decrease in ozone up to 100 Dobson Units (DU) in the Eastern Hemisphere and over 150 DU in the Western Hemisphere. In this case, the photochemical destruction of ozone in both the Western and Eastern Hemispheres at a maximum was about 50 DU with peaks in April in the Eastern Hemisphere and in March and April in the Western Hemisphere. Heterogeneous activation of halogen gases on the surface of polar stratospheric clouds, on the one hand, led to a sharp increase in the destruction of ozone in chlorine and bromine catalytic cycles, and, on the other hand, decreased its destruction in nitrogen catalytic cycles. Analysis of wave activity using 3D Plumb fluxes showed that the enhancement of upward wave activity propagation in the middle of March over the Gulf of Alaska was observed during the development stage of the minor sudden stratospheric warming (SSW) event that led to displacement of the stratospheric polar vortex to the north of Canada and decrease of polar stratospheric clouds’ volume.

Numerical Modeling of the Influence of Physical and Chemical Factors on the Interannual Variability of Antarctic Ozone

The variability of Antarctic total column ozone in 1980–2018 is considered. The study analyzes trends in Antarctic total column ozone during the study period as well as the physical and chemical processes affecting the seasonal variability of total column ozone. The main attention is paid to the influence of dynamical processes on the stability of the Antarctic polar vortex, to the formation of polar stratospheric clouds, and to the influence of gas-phase and heterogeneous processes on the surface of polar stratospheric clouds and sulfate aerosol. The method of research is the analysis of the results of ground and satellite observations and numerical modeling of physical and chemical processes over the Antarctic using a global chemistry transport model with the dynamical parameters specified from reanalysis data.

Improvements to stratospheric chemistry scheme in the UM-UKCA (v10.7) model: solar cycle and heterogeneous reactions

Abstract. Improvements are made to two areas of the United Kingdom Chemistry and Aerosol (UKCA) module, which forms part of the Met Office Unified Model (UM) used for weather and climate applications. Firstly, a solar cycle is added to the photolysis scheme. The effect on total column ozone of this addition was found to be around 1 %–2 % in midlatitude and equatorial regions, in phase with the solar cycle. Secondly, reactions occurring on the surfaces of polar stratospheric clouds and sulfate aerosol are updated and extended by modification of the uptake coefficients of five existing reactions and the addition of a further eight reactions involving bromine species. These modifications are shown to reduce the overabundance of modelled total column ozone in the Arctic during October to February, southern midlatitudes during August and the Antarctic during September. Antarctic springtime ozone depletion is shown to be enhanced by 25 DU on average, which now causes the ozone hole to be somewhat too deep compared to observations. We show that this is in part due to a cold bias of the Antarctic polar vortex in the model.

The Antarctic ozone depletion caused by Erebus volcano gas emissions

Abstract Heterogeneous chemical reactions releasing photochemically active molecular chlorine play a key role in Antarctic stratospheric ozone destruction, resulting in the Antarctic ozone hole. Hydrogen chloride (HCl) is one of the principal components in these reactions on the surfaces of polar stratospheric clouds (PSCs). PSCs form during polar nights at extremely low temperatures (lower than −78 °C) mainly on sulfuric acid (H2SO4) aerosols, acting as condensation nuclei and formed from sulfur dioxide (SO2). However, the cause of HCl and H2SO4 high concentrations in the Antarctic stratosphere, leading to considerable springtime ozone depletion, is still not clear. Based on the NCEP/NCAR reanalysis data over the last 35 years and by using the NOAA HYSPLIT trajectory model, we show that Erebus volcano gas emissions (including HCl and SO2) can reach the Antarctic stratosphere via high-latitude cyclones with the annual average probability P ¯ ann . of at least ∼0.235 (23.5%). Depending on Erebus activity, this corresponds to additional annual stratospheric HCl mass of 1.0–14.3 kilotons (kt) and SO2 mass of 1.4–19.7 kt. Thus, Erebus volcano is the natural and powerful source of additional stratospheric HCl and SO2, and hence, the cause of the Antarctic ozone depletion, together with man-made chlorofluorocarbons.

Do cosmic-ray-driven electron-induced reactions impact stratospheric ozone depletion and global climate change?

Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to explain polar ozone depletion and surface temperature change. It was proposed that the dissociation of chlorofluorocarbons (CFCs) on ice surfaces of polar stratospheric clouds plays the dominant role in forming the ozone hole. Efforts have been made to predict polar ozone loss in future years. It was further proposed that CFCs and cosmic-ray-driven ozone depletion may control global surface temperatures. These assertions challenge the fundamental understanding of Antarctic stratospheric ozone loss and global warming. Here we show that these arguments based on the CRE mechanism are inconclusive. First, correlations of satellite data of CFC-12, N2O and CH4 from ACE-FTS show no evidence of significant loss of CFC-12 as predicted by the CRE mechanism. Second, conclusions drawn about a possible CRE impact on the atmosphere, based on correlations of different observed atmospheric parameters, do not have a physical basis. Finally, predictions on the future development of the atmosphere based on these correlations are not reliable for either the ozone hole or global surface temperatures.

Theoretical study of atmospheric clusters: HNO3–HCl–H2O

Nitric acid, hydrochloric acid and water can form stable aggregates with atmospheric implications, for instance at the surface of polar stratospheric clouds. The structure, stability and chemical properties of these ternary complexes are studied by means of high level theoretical calculations (hybrid DFT B3LYP method along with aug-cc-pVQZ basis set). From the many possible systems that these molecules could form, only 15 are found to yield stable structures, well characterized by a minimum in their potential energy surfaces. These aggregates are studied in detail. They can be collected in three families, according to the role played by each species in the different hydrogen bonding links that result and provide the basis for the stabilization of the clusters. Water and HCl can be H-donors to almost every O atom of HNO(3), which in turn can donate its H atom to the other two molecules. Two special cases are found, one in which H(2)O plays a central role, and another with a three-dimensional structure, in contrast to the basically planar frame of the other clusters. Bonding properties are investigated for the whole series using AIM methods. The elongation of the H-Cl bond as a consequence of the aggregate creation is inspected in detail, as it may provide a clue to the lability of this molecule with implications in atmospheric processes. The Gibbs free energy calculated for these clusters shows that some of them could form spontaneously in the range of temperatures of the stratosphere.

Combined chemistry-climate model of the atmosphere

A combined three-dimensional global model of the chemistry and dynamics of the lower and middle atmosphere (up to 90 km from the Earth’s surface) is described. With the use of this model within the AMIP2 (1979–1995) program, numerical calculations were performed with consideration for the interactive coupling between the ozone content, radiation heating, and atmospheric circulation. Comparisons were made between calculated and observed data on the ozone content and temperature. Heterogeneous processes on the surface of polar stratospheric clouds were shown to be important for a correct simulation of the spatial and temporal distribution of atmospheric ozone.

Impact of cosmic rays on stratospheric chlorine chemistry and ozone depletion.

Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar stratospheric clouds (PSC) has been suggested as playing a significant role in causing the ozone hole. However, observed stratospheric CFC distributions are inconsistent with a destruction of CFC on PSC surfaces and no significant correlation exists between ozone levels and cosmic-ray activity inside the polar regions. Model simulations indicate that this mechanism can have only a limited impact on chemical ozone loss and thus on the recovery of stratospheric ozone.

Spectrometric measurements of NO 2 slant column amount at Stara Zagora Station (42°N, 25°E)

Nitrogen dioxide (NO 2) is a representative of a family of chemically very active radicals NO x=NO+NO 2. These radicals catalytically destroy the ozone and play a significant role in other ozone-destroying catalytic cycles. In the polar night NO 2 can deactivate ClO by a termolecular reaction to form the reservoir gas Cl0NO 2. In this way NO 2 restricts the ozone destruction in the polar vortex. NO 2 also takes part in heterogeneous reactions, which occur on the surface of polar stratospheric clouds. For the trace gases study and particularly for the nitrogen dioxide a spectrometric instrument GASCOD-BG was installed at the Solar Terrestrial Influences Laboratory - Bulgarian Academy of Sciences , Stara Zagora Department in August 1999. The instrument was developed at the Institute of Atmospheric and Oceanic Sciences at the Council of National Research, Italy, Bologna. The results of the NO 2 observation for more than two years are presented in this paper.

Chemical depletion of Arctic ozone in winter 1999/2000

During Arctic winters with a cold, stable stratospheric circulation, reactions on the surface of polar stratospheric clouds (PSCs) lead to elevated abundances of chlorine monoxide (ClO) that, in the presence of sunlight, destroy ozone. Here we show that PSCs were more widespread during the 1999/2000 Arctic winter than for any other Arctic winter in the past two decades. We have used three fundamentally different approaches to derive the degree of chemical ozone loss from ozonesonde, balloon, aircraft, and satellite instruments. We show that the ozone losses derived from these different instruments and approaches agree very well, resulting in a high level of confidence in the results. Chemical processes led to a 70% reduction of ozone for a region ∼1 km thick of the lower stratosphere, the largest degree of local loss ever reported for the Arctic. The Match analysis of ozonesonde data shows that the accumulated chemical loss of ozone inside the Arctic vortex totaled 117 ± 14 Dobson units (DU) by the end of winter. This loss, combined with dynamical redistribution of air parcels, resulted in a 88 ± 13 DU reduction in total column ozone compared to the amount that would have been present in the absence of any chemical loss. The chemical loss of ozone throughout the winter was nearly balanced by dynamical resupply of ozone to the vortex, resulting in a relatively constant value of total ozone of 340 ± 50 DU between early January and late March. This observation of nearly constant total ozone in the Arctic vortex is in contrast to the increase of total column ozone between January and March that is observed during most years.

Direct Experimental Evidence for Reactions between Dissolved Acid Halide and Chlorine Nitrate

Cluster chemistry employing a fast flow reactor was used to evaluate the enhanced reactivity of chlorine nitrate (ClONO2) with dissolved acid halide. Reactions of ClONO2 with deuterium chloride doped deuterated water clusters [D+(D2O)m(DCl)n, (m = 10−14, n = 1,2)] were investigated under thermal conditions over a temperature range of 148−158 K; deuterated species were employed in place of light hydrogen containing molecules to facilitate the determination of reaction mechanisms. Chemical reactions were found to occur between water clusters and chlorine nitrate only under conditions where dissolved deuterium chloride was present. Nitric acid is found to remain within the water cluster to yield gaseous chlorine (Cl2) from the water cluster. These results provide direct evidence that an ionic reaction mechanism is involved in the heterogeneous reaction of hydrogen chloride and chlorine nitrate on clusters that mimic polar stratospheric cloud surfaces.

Stratospheric ozone depletion: A review of concepts and history

Stratospheric ozone depletion through catalytic chemistry involving man‐made chlorofluorocarbons is an area of focus in the study of geophysics and one of the global environmental issues of the twentieth century. This review presents a brief history of the science of ozone depletion and describes a conceptual framework to explain the key processes involved, with a focus on chemistry. Observations that may be considered as evidence (fingerprints) of ozone depletion due to chlorofluorocarbons are explored, and the related gas phase and surface chemistry is described. Observations of ozone and of chlorine‐related trace gases near 40 km provide evidence that gas phase chemistry has indeed currently depleted about 10% of the stratospheric ozone there as predicted, and the vertical and horizontal structures of this depletion are fingerprints for that process. More striking changes are observed each austral spring in Antarctica, where about half of the total ozone column is depleted each September, forming the Antarctic ozone hole. Measurements of large amounts of ClO, a key ozone destruction catalyst, are among the fingerprints showing that human releases of chlorofluorocarbons are the primary cause of this change. Enhanced ozone depletion in the Antarctic and Arctic regions is linked to heterogeneous chlorine chemistry that occurs on the surfaces of polar stratospheric clouds at cold temperatures. Observations also show that some of the same heterogeneous chemistry occurs on the surfaces of particles present at midlatitudes as well, and the abundances of these particles are enhanced following explosive volcanic eruptions. The partitioning of chlorine between active forms that destroy ozone and inert reservoirs that sequester it is a central part of the framework for our understanding of the 40‐km ozone decline, the Antarctic ozone hole, the recent Arctic ozone losses in particularly cold years, and the observation of record midlatitude ozone depletion after the major eruption of Mount Pinatubo in the early 1990s. As human use of chlorofluorocarbons continues to decrease, these changes throughout the ozone layer are expected to gradually reverse during the twenty‐first century.

Adsorption and Desorption of HCl on Ice

Pulsed molecular beam and mass spectrometric techniques are used to study the adsorption of hydrogen chloride on thin ice films at temperatures from 100 to 170 K. The adsorption and desorption of HCl from an ice surface is relevant to the polar stratosphere where it is thought that chlorine atoms are liberated from reservoir species such as HCl by heterogeneous reactions occurring on the surface of polar stratospheric clouds. We have measured the sticking coefficient for HCl at an incident translational energy of 0.09 eV on thin film ice surfaces using a modified version of the reflectivity technique of King and Wells. By modeling the HCl partial pressure versus time waveforms for surface temperatures of 100−125 K, we obtain a sticking coefficient of 0.91 ± 0.06. The model incorporates first-order HCl desorption and a loss term also first order in HCl. Fitted kinetic parameters are Edes = 28 kJ/mol, νdes = 2 × 1014 s-1 for desorption and Eloss = 21 kJ/mol, νloss = 4 × 1011 s-1 for the loss. The loss may be associated with the onset of water diffusion on the ice surface and subsequent ionization or hydration of the HCl. The measured waveforms are inconsistent with diffusion of HCl into the bulk. The apparent reflectivity decreases substantially in the temperature range of 126 to 140 K. This decrease cannot be attributed to an increase in sticking coefficient, a phase change in the ice, or the formation of the hexahydrate state of HCl.

Impact of stratospheric dynamics and chemistry on northern hemisphere midlatitude ozone loss

The importance of dynamics for stratospheric ozone distribution in the northern hemisphere is investigated by using multiannual simulations of the coupled dynamic‐chemical general circulation model ECHAM3/CHEM. This model includes a parameterization for heterogeneous reactions on the surfaces of polar stratospheric clouds (PSCs) and on sulfate aerosols. A warm and a cold stratospheric winter are examined to estimate the range of chemical ozone loss in the model due to heterogeneous reactions on PSCs. Ozone depletion in the model mainly occurs inside the polar vortex. An additional ozone reduction due to heterogeneous reactions on PSCs is found outside the polar vortex. Secondary vortex formation and vortex contraction after an elongation lead to a transport of air masses with chemically reduced ozone values out of the vortex. Except for such events the edge of the modeled polar vortex acts as a barrier to transport. During the formation of secondary vortices no additional heterogeneous reactions occur therein. Other dynamic events, such as the elongation of the polar vortex and its displacement to lower latitudes, lead to an intense ozone depletion. A minor stratospheric warming in the model causes a total deactivation of chlorine compounds and prevents further ozone depletion. In midlatitudes, the amplitude of short‐term variations of total ozone is amplified by PSC heterogeneous chemical ozone reduction.

A three-dimensional model simulation of the impact of Mt. Pinatubo aerosol on the Antarctic ozone hole

Seasonal integrations of a three-dimensional fully coupled model of the radiation, dynamics and chemistry of the stratosphere and mesosphere are presented for the southern hemisphere spring. Included in the model are heterogeneous reactions which take place in sulphuric acid aerosol droplets as well as on the surface of Polar Stratospheric Clouds (PSCs). Calculations are performed for background levels of stratospheric aerosol and for conditions following the eruption of Mt. Pinatubo. For the volcanic case, surface area densities are derived from Improved Stratospheric and Mesospheric Sounder data. For background aerosol loadings there are significant increases in HOx and CIOx, as well as reductions in NOx. These effects are enhanced following the Pinatubo eruption but saturate at relatively low aerosol levels and hence can persist in the stratosphere for several years. Where PSCs are predicted to form, the sulphate aerosol chemistry does not operate in the model since the aerosols are incorporated as nuclei within the PSCs. In contrast, on the edge of the ozone hole, where temperatures are only just too high for the formation of PSCs, destruction by aerosol can result in further total ozone depletion of order 20 Dobson Units. In addition, the size and duration of the ozone hole are both increased by the presence of volcanic aerosols. The results support previous suggestions that the eruption of Mt. Pinatubo resulted in a temporary increase in ozone depletion over Antarctica and elsewhere.

A three‐dimensional model simulation of the impact of Mt. Pinatubo aerosol on the Antarctic ozone hole

AbstractSeasonal integrations of a three‐dimensional fully coupled model of the radiation, dynamics and chemistry of the stratosphere and mesosphere are presented for the southern hemisphere spring. Included in the model are heterogeneous reactions which take place in sulphuric acid aerosol droplets as well as on the surface of Polar Stratospheric Clouds (PSCs). Calculations are performed for background levels of stratospheric aerosol and for conditions following the eruption of Mt. Pinatubo. For the volcanic case, surface area densities are derived from Improved Stratospheric and Mesospheric Sounder data. For background aerosol loadings there are significant increases in HOx and CIOx, as well as reductions in NOx. These effects are enhanced following the Pinatubo eruption but saturate at relatively low aerosol levels and hence can persist in the stratosphere for several years. Where PSCs are predicted to form, the sulphate aerosol chemistry does not operate in the model since the aerosols are incorporated as nuclei within the PSCs. In contrast, on the edge of the ozone hole, where temperatures are only just too high for the formation of PSCs, destruction by aerosol can result in further total ozone depletion of order 20 Dobson Units. In addition, the size and duration of the ozone hole are both increased by the presence of volcanic aerosols. The results support previous suggestions that the eruption of Mt. Pinatubo resulted in a temporary increase in ozone depletion over Antarctica and elsewhere.

Ozone mass exchange between the stratosphere and troposphere for background and volcanic sulfate aerosol conditions

A three‐dimensional global chemical/dynamical model is used to study ozone mass exchange between the stratosphere and the troposphere. The ozone budget is calculated in the northern and southern extratropical lowermost stratosphere and in the tropical upper troposphere during both perturbed and background aerosol conditions. The stratospheric ozone mass flux into the troposphere is highest during the spring months in both hemispheres and higher in the northern hemisphere than in the southern hemisphere. During background aerosol conditions the net modeled stratospheric flux of ozone to the troposphere is 792 Tg/yr. The results suggest that the heterogeneous chemical reactions occurring on the surface of sulfate aerosols can have a significant impact on the ozone mass flux across the tropopause, leading to a possible 15% reduction in the annual global ozone mass transported from the stratosphere to the troposphere after a large volcanic eruption. Most of the reduction in ozone mass flux occurs in the northern hemisphere. In the southern hemisphere winter and spring the ozone concentration is already significantly perturbed by the heterogeneous reactions occurring on the surface of polar stratospheric clouds over Antarctica. The further increase in heterogeneous conversion due to the enhanced sulfate aerosol produces a smaller increase in active chlorine (ClO) than in the northern hemisphere, leading to a smaller increase in ozone destruction.

Decadal evolution of total ozone decline: Observations and model results

In this study we examine the rate of change in the total ozone decline observed during past years over both the northern and the southern hemisphere. This is studied from the analysis of the longest available reevaluated series of total ozone observations (1964–1993), with the aid of a two‐dimensional chemical/transport model of the middle atmosphere, which takes into account microphysical formation of polar stratospheric clouds (PSCs) and heterogeneous mechanisms under different stratospheric chlorine‐loading conditions. In our analysis the zonal mean total ozone decreases during the last two decades were compared to the corresponding mean ozone levels during the undisturbed period 1964–1973. The effects of quasi‐cyclical and transient phenomena such as the quasi‐biennial oscillation, the El Nino/Southern Oscillation and the solar cycle, which are known to significantly influence the ozone variability, have been filtered out from the observations, allowing a more straightforward comparison between model results and observations. These model results are in good agreement with the observed change in the rate of total ozone decline over the middle to high latitudes of both the northern and the southern hemisphere. These model calculations indicate that the ozone depletion at high latitudes in both hemispheres is mainly caused by heterogeneous reactions on the surface of PSCs. At northern midlatitudes, though, the ozone losses are caused by heterogeneous reactions on the surface of sulfate aerosols, especially after large volcanic eruptions. From a sensitivity study performed with the model, a 2° decrease in temperature was found to affect significantly the ozone field, especially in the northern hemisphere, by facilitating the heterogeneous conversion processes on PSC surfaces through enhancement of their concentration, and by accelerating the reactions on the surface of sulfate aerosols.

Morphology and Surface Areas of Thin Ice Films

Thin ice films formed by deposition from the vapor phase in a fast flow-tube reactor have been used to simulate polar stratospheric cloud surfaces in order to obtain laboratory data on uptake and heterogeneous reaction rates.

A three‐dimensional simulation of the Antarctic ozone hole: Impact of anthropogenic chlorine on the lower stratosphere and upper troposphere

We have developed a global three‐dimensional transport‐chemical model of the stratosphere (called the Study of Transport and chemical Reactions in the Stratosphere (STARS)) which includes a representation of the formation of polar stratospheric clouds (PSCs) and heterogeneous reactions on the surfaces of PSCs and sulfate aerosols. The formation of the observed springtime “Antarctic ozone hole” is well reproduced by the model. A maximum of 40% total ozone depletion occurs in October. Calculated ozone and chlorine concentrations are consistent with satellite observations. After the breakdown of the polar vortex in December, air with depleted ozone is transported to midlatitudes in the southern hemisphere, resulting in a 2–4% ozone decrease at 50°S in December and a 1% decrease in the sub tropics. Ozone‐poor air masses are also transported to the troposphere and produce a significant decrease in upper tropospheric ozone. Model calculations show that the calculated ozone depletion is not significantly modified when type I PSC particles are assumed to be liquid ternary solutions (H2SO4/HNO3/H2O) rather than solid nitric acid trihydrates. Ice particles (type II PSCs) sediment into the troposphere, producing a large decrease in the concentrations of stratospheric HNO3 and NO2. As a result, the conversion of ClO into ClONO2 is reduced, and the concentration of reactive chlorine remains high for two additional weeks. The ozone column abundance is reduced by an additional 10% during the month of October. The model results show that the ozone minimum observed in Antarctica several decades ago (preindustrial chlorine levels) is produced by (natural) dynamical processes. Under these conditions the polar ozone depletion caused by chemical processes was very small (maximum of 3%) in October. In November the ozone concentration even increased above 22 km in response to PSC processes.