Impact of ozone mini-holes on the heterogeneous destruction of stratospheric ozone

A comprehensive study of ozone mini-holes over the mid-latitudes of both hemispheres is presented, based on model simulations with the coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM representing atmospheric conditions in 1960, 1980, 1990 and 2015. Ozone mini-holes are synoptic-scale regions of strongly reduced total ozone, directly associated with tropospheric weather systems. Mini-holes are supposed to have chemical and dynamical impacts on ozone levels. Since ozone levels over northern mid-latitudes show a negative trend of approximately -4%/decade and since it exists a negative correlation between total column ozone and erythemally active solar UV-radiation reaching the surface it is important to understand and assess the processes leading to the observed ozone decline. The simulated mini-hole events are validated with a mini-hole climatology based on daily ozone measurements with the TOMS (total ozone mapping spectrometer) instrument on the satellite Nimbus-7 between 1979 and 1993. Furthermore, possible trends in the event frequency and intensity over the simulation period are assessed. In the northern hemisphere the number of mini-hole events in early winter decreases between 1960 and 1990 and increases towards 2015. In the southern hemisphere a positive trend in mini-hole event frequency is detected between 1960 and 2015 in spring associated with the increasing Antarctic Ozone Hole. Finally, the impact of mini-holes on the stratospheric heterogeneous ozone chemistry is investigated. For this purpose, a computer-based detection routine for mini-holes was developed for the use in ECHAM4.L39(DLR)/CHEM. This method prevents polar stratospheric cloud formation and therefore heterogeneous ozone depletion inside mini-holes. Heterogeneous processes inside mini-holes amount to one third of heterogeneous ozone destruction in general over northern mid- and high-latitudes during winter (January-April) in the simulation.     

Statistical analysis of stratospheric ozone data for the detection of trends

Time series modelling of monthly total ozone data is considered for the detection of trend in ozone due to the possible effects of the release of chloroftuoromethanes (CFMs). Based on ozone data from a global network of 36 ground-based Dobson recording stations over the period 1958–1978. our findings show little evidence of any trend in global ozone occurring in the 1970s. Using a random effects model for the individual station trend estimates, the global change in total ozone during 1970–1978 has been estimated as (0.28 ± 1.35)%. These results differ considerably from the theoretical CFM chemical model predictions of (−1.5 ±1.1)% change.     

Depletion of stratospheric ozone over the Antarctic and Arctic: responses of plants of polar terrestrial ecosystems to enhanced UV-B, an overview

Depletion of stratospheric ozone over the Antarctic has been re-occurring yearly since 1974, leading to enhanced UV-B radiation. Arctic ozone depletion has been observed since 1990. Ozone recovery has been predicted by 2050, but no signs of recovery occur. Here we review responses of polar plants to experimentally varied UV-B through supplementation or exclusion. In supplementation studies comparing ambient and above ambient UV-B, no effect on growth occurred. UV-B-induced DNA damage, as measured in polar bryophytes, is repaired overnight by photoreactivation. With UV exclusion, growth at near ambient may be less than at below ambient UV-B levels, which relates to the UV response curve of polar plants. UV-B screening foils also alter PAR, humidity, and temperature and interactions of UV with environmental factors may occur. Plant phenolics induced by solar UV-B, as in pollen, spores and lignin, may serve as a climate proxy for past UV. Since the Antarctic and Arctic terrestrial ecosystems differ essentially, (e.g. higher species diversity and more trophic interactions in the Arctic), generalization of polar plant responses to UV-B needs caution.     

Implications of smaller concentrations of stratospheric OH: A two-dimensional model study of ozone perturbations

There is growing observational evidence that stratospheric OH concentrations are smaller than models have been predicting. Using very recent HO_x reaction rate coefficient measurements in a two-dimensional photochemical model, results which support these observations are obtained. As a consequence of smaller OH concentrations, we show that perturbations of stratospheric ozone by NO_x (SST emissions and nitrogen fertilizers) may be larger than expected, while perturbations due to added water vapor and chlorine (SSTs and chlorofiuoromethanes. respectively) may be smaller.     

The extraordinary events of the major,sudden stratospheric warming,the diminutive antarctic ozone hole,and its split in 2002

GOAL, SCOPE AND BACKGROUND: Great interest in the unprecedented events of the major, sudden stratospheric warming and the ozone hole split over Antarctica in September 25, 2002 motivates a necessity to analyze the current understanding on the dynamics, chemistry and climate impacts that are associated with both events. METHODS: Significant progress in the analysis of the observational data obtained, as well as successful development and application of dynamical modeling, which have been achieved very recently, create a basis for the first survey on the role of the major, sudden stratospheric warming observed in the southern hemisphere and its relationship to the diminutive Antarctic ozone hole and its break up into two parts. RESULTS AND DISCUSSION: Special attention has been paid to assessments of the causes of the major warming event and the future expectations concerning the stratospheric ozone depletion effect. Among the principal results is the fact that, as the polar vortex elongated, it became hydrodynamically unstable, and this insta-, bility affected the upper troposphere and stratosphere. During the major, sudden stratospheric warming, the middle stratospheric vortex split into two pieces; one piece rapidly mixed with extra vortex air, while the other returned to the pole as a much weaker and smaller vortex. The polar night jet was considerably weaker than normal, and was displaced more poleward than has been observed in previous winters, resulting from a series of wave events (propagated from the troposphere) that took place over the course of the winter. Finally, the relative ozone decrease (increase) in the eastern Antarctic is tightly associated with westerly (easterly) zonal wind anomalies near the southern tip of South America, and the unusual behavior of the ozone hole in 2002 therefore appears to be caused by great easterlies in this region. CONCLUSIONS: The main conclusion is that the southern polar vortex and the diminutive ozone hole split into two parts in September 2002, due to the prevalence of very strong planetary waves, led to the appearance of a major, sudden stratospheric warming. Although there is evidence that sea surface temperature anomalies contributed to the excitation of the quite strong planetary waves over Antarctica in 2002, there is not yet a widely approved mechanism supporting that. RECOMMENDATIONS AND OUTLOOK:The appearance of the near-record size of the 2003 ozone hole confirmed that the 'no-ozone-hole' episode observed in the year 2002 does not denote a recovery of the ozone layer. Despite the current successful attempts to get a sufficient understanding for the genesis of both extraordinary events, more observations and further modeling efforts are necessary to more reliably assess the contribution of various dynamic mechanisms to the recently observed tropo-stratospheric surprises.     

Factors affecting the ozone sensitivity of temperate European grasslands: an overview

This overview of experimentally induced effects of ozone aims to identify physiological and ecological principles, which can be used to classify the sensitivity to ozone of temperate grassland communities in Europe. The analysis of data from experiments with single plants, binary mixtures and multi-species communities illustrates the difficulties to relate individual responses to communities, and thus to identify grassland communities most at risk. Although there is increasing evidence that communities can be separated into broad classes of ozone sensitivity, the database from experiments under realistic conditions with representative systems is too small to draw firm conclusions. But it appears that risk assessments, based on results from individuals or immature mixtures exposed in chambers, are only applicable to intensively managed, productive grasslands, and that the risk of ozone damage for most of perennial grasslands with lower productivity tends to be less than previously expected.     

Retrospective bioindication of stratospheric ozone and ultraviolet radiation using hydroxycinnamic acid derivatives of herbarium samples of an aquatic liverwort

We analyzed bulk UV absorbance of methanolic extracts and levels of five UV-absorbing compounds (hydroxycinnamic acid derivatives) in 135 herbarium samples of the liverwort Jungermannia exsertifolia subsp. cordifolia from northern Europe. Samples had been collected in 1850–2006 (96% in June–August). Both UV absorbance and compound levels were correlated positively with collection year. p-Coumaroylmalic acid (C1) was the only compound showing a significant (and negative) correlation with stratospheric ozone and UV irradiance in the period that real data of these variables existed. Stratospheric ozone reconstruction (1850–2006) based on C1 showed higher values in June than in July and August, which coincides with the normal monthly variation of ozone. Combining all the data, there was no long-term temporal trend from 1850 to 2006. Reconstructed UV showed higher values in June–July than in August, but again no temporal trend was detected in 1918–2006 using the joint data. This agrees with previous UV reconstructions.     

The photochemistry of ozone

This review surveys laboratory data concerning the photochemistry of ozone, and indicates the relevance of the laboratory studies to interpretations of atmospheric chemistry. Emphasis is placed on the nature of the electronic states of the atomic and molecular oxygen fragments of photolysis, and the efficiencies with which the various species are formed. The primary quantum yield for O(¹D) formation is certainly less than unity for λ < 274 nm, and it may thus also be less than unity in the atmospherically critical region around λ = 300 nm. Similar considerations are likely to apply to the efficiency of formation of excited singlet molecular oxygen, O₂(¹Δ_g). On the other hand, O₂(¹Δ_g) seems to be formed with high efficiency at wavelengths longer than the λ ∼- 310nm threshold for O(¹D) production. Calculations of atmospheric [O₃] that depend on measurement of the intensity of the O₂(¹Δ→ ³Σ_g⁻) infrared atmospheric band may therefore be in error both if they assume a quantum yield of unity for O₂(¹Δ_g) production at λ < 310 nm and if they assume that the quantum yield is zero at longer wavelengths. The wavelength dependences of the quantum efficiencies are interpreted in terms of the spectroscopy of ozone; evidence for the breakdown of simple spin conservation arguments is presented, and some explanations for the behaviour are suggested. Photofragment energy analysis, coherent Raman, and fluorescence techniques have been used to probe details of the dissociation dynamics. Results from some of these experiments are used to show how further information needed for atmospheric studies may eventually be won.     

The pressure drop across a packed-bed collector of low-concentration stratospheric gases

Packed beds of molecular-sieve pellets have found application in the high-altitude collection of certain gases present in the atmosphere in low concentrations. To facilitate the design of such low-pressure gas samplers, a theory is developed establishing practical relations between pressure drop, gas flow rate, and various gas and packing characteristics. Pressure-drop vs flow-rate relations are confirmed experimentally over the range of ambient pressures of 0.0013-0.79 atm, and for conditions of flow that may be either viscous or inertial, compressible or incompressible, or with or without molecular slip.The theory shows that, for a given set of experimental conditions, there exists a critical gas velocity below which a pressure drop and its associated velocity are possible, if at all, at only a single ambient pressure. Above the critical velocity, however, a given pressure drop-velocity combination may occur, if at all, at either one or two ambient pressures.Methods are described for correlating experimental data in terms of dimensionless groups and, on the basis of relatively few measurements near atmospheric conditions, for estimating pressure drop over a broad range of ambient pressures and gas velocities.The theory derived is thought to be applicable, under appropriate conditions, to a variety of porous media including fibrous filters.     

Evidence for potential impacts of ozone on Pinus cembra L. at mountain sites in Europe: an overview

We summarize what is known about the impact of ozone (O(3)) on Pinus cembra in the timberline ecotone of the central European Alps and the Carpathian Mountains. In the central European Alps exposure to ambient and two-fold ambient O(3) throughout one growing season did neither cause any visible injury nor affect the photosynthetic machinery and biochemical parameters in current to 1-year-old needles. By contrast, in the southern French Alps and in the Carpathians 1-year-old needles of Pinus cembra trees showed visual symptoms similar to those observed in O(3) stressed pine stands in southern California. For the southern French Alps the observed symptoms could clearly be attributed O(3) and differences in O(3) uptake seems to be the likely key factor for explaining the observed decline. For the Carpathians however, other reasons such as drought may not be excluded in eliciting the observed symptoms. Thus, the action of O(3) has always to be evaluated in concert with other environmental impacts, determining the tree's sensitivity to stress.     

The ozone formation potential of 1-bromo-propane

1-Bromo-propane (1-BP) is a replacement for high-end chlorofluorocarbon (HCFC) solvents. Its reaction rate constant with the OH radical is, on a weight basis, significantly less than that of ethane. However, the overall smog formation chemistry of 1-BP appears to be very unusual compared with typical volatile organic compounds (VOCs) and relatively complex because of the presence of bromine. In smog chamber experiments, 1-BP initially shows a faster ozone build-up than what would be expected from ethane, but the secondary products containing bromine tend to destroy ozone such that 1-BP can have a net overall negative reactivity. Alternative sets of reactions are offered to explain this unusual behavior. Follow-up studies are suggested to resolve the chemistry. Using one set of bromine-related reactions in a photochemical grid model shows that 1-BP would be less reactive toward peak ozone formation than ethane with a trend toward even lower ozone impacts in the future.     

Risks to the stratospheric ozone shield in the Anthropocene: This article belongs to Ambio’s 50th Anniversary Collection. Theme: Ozone Layer

Crutzen (1974) and Crutzen and Ehhalt (1977) presented two key papers in Ambio that in Ambioexemplify how science first revealed to humankind the potential for damage to our ozone shield in the Anthropocene. Crutzen’s (1974) review is a sweeping summary of the risks to the ozone layer from supersonic aircraft, chlorofluorocarbons, as well as nuclear weapons testing and nuclear war. Crutzen and Ehhalt (1977) described how the nitrous oxide produced from fertilizers could pose another threat to the stability of the stratospheric ozone layer. The two papers are part of a body of influential scientific work that led to the pioneering Montreal Protocol to Protect the Earth’s Ozone Layer to phase out production of chlorofluorocarbons (in 1987), as well as national decisions that slowed or stopped production of supersonic planes (in the 1970s). They remain guideposts today for ongoing international negotiations regarding reducing emissions from fertilizer and limiting nuclear testing.     

The effects of meteorology on ozone in urban areas and their use in assessing ozone trends

The United States Environmental Protection Agency issues periodic reports that describe air quality trends in the US. For some pollutants, such as ozone, both observed and meteorologically adjusted trends are displayed. This paper describes an improved statistical methodology for meteorologically adjusting ozone trends as well as characterizes the relationships between individual meteorological parameters and ozone. A generalized linear model that accommodates the nonlinear effects of the meteorological variables was fit to data collected for 39 major eastern US urban areas. Overall, the model performs very well, yielding R² statistics as high as 0.80. The analysis confirms that ozone is generally increasing with increasing temperature and decreasing with increasing relative humidity. Examination of the spatial gradients of these responses show that the effect of temperature on ozone is most pronounced in the north while the opposite is true of relative humidity. By including HYSPLIT-derived transport wind direction and distance in the model, it is shown that the largest incremental impact of wind direction on ozone occurs along the periphery of the study domain, which encompasses major NO_x emission sources.     

The southern hemisphere ozone hole split in 2002

Among the most important aspects of the atmospheric pollution problem are the anthropogenic impacts on the stratospheric ozone layer, the related trends of the total ozone content drop and the solar ultraviolet radiation enhancement at the Earth's surface level. During September 2002, the ozone hole over the Antarctic was much smaller than in the previous six years. It has split into two separate holes, due to the appearance of sudden stratospheric warming that has never been observed before in the southern hemisphere. The analysis of this unprecedented event is attempted, regarding both the meteorological and photochemical aspects, in terms of the unusual thermal field patterns and the induced polar vortex disturbances.     

Fine-scale layering on the edge of a stratospheric intrusion

Observations of vertical profiles of ozone, humidity, static stability and VHF radar vertical power at Aberystwyth (52°N, 4°W) on 21 June 1996 revealed a pronounced layered structure at the western edge of a stratospheric intrusion, in a location where one would expect to see a tropopause fold. Despite the 3 km depth of the observed ozone anomaly, it was not represented as a fold in the ECMWF potential vorticity analyses; nor was it evident as a layer of enhanced wind shear. Ozone lidar measurements suggest that the fine-scale layering gave way to a single layer as the day progressed. Weak sporadic turbulence observed by the radar at the edge of the fold showed some mixing between stratospheric and tropospheric air.     

The health benefits of reduced tropospheric ozone in California

Californians are exposed daily to concentrations of ozone (O3) that are among the highest in the United States. Recently, the state adopted a new 8-hr ambient standard of 0.070 ppm, more stringent than the current federal standard. The new standard is based on controlled human studies and on dozens of epidemiologic studies reporting associations between O3 at current ambient levels and a wide range of adverse health outcomes. Clearly, the new O3 standards will require further reductions in the precursor pollutants and additional expenditures for pollution control. Therefore, it is important to quantify the incremental health benefits of moving from current conditions to the new California standard. In this paper, a standard methodology is applied to quantify the health benefits associated with O3 concentration reductions in California. O3 concentration reductions are estimated using ambient monitoring data and a proportional rollback approach in which changes are specific to each air basin, and control strategies may impact concentrations both below and above the standard. Health impacts are based on published epidemiologic studies, including O3-related mortality and morbidity, and economic values are assigned to these outcomes based on willingness-to-pay and cost-of-illness studies. Central estimates of this research indicate that attaining the California 8-hr standard, relative to current concentrations, would result in annual reductions of 630 cases of premature mortality, 4200 respiratory hospital admissions, 660 pediatric emergency room visits for asthma, 4.7 million days of school loss, and 3.1 million minor restricted activity days, with a median estimated economic value of dollar 4.5 billion. Sensitivity analyses indicate that these findings are robust with respect to exposure assessment methods but are influenced by assumptions about the slope of the concentration-response function in threshold models and the magnitude of the O3-mortality relationship. Although uncertainties exist for several components of the methodology, these results indicate that the benefits of reducing O3 to the California standard may be substantial and that further research on the shape of the O3-mortality concentration-response function and economic value of O3-related mortality would best reduce these uncertainties.     

Predicting ozone levels

This paper presents a statistical model that is capable of predicting ozone levels from precursor concentrations and meteorological conditions during daylight hours in the Shuaiba Industrial Area (SIA) of Kuwait. The model has been developed from ambient air quality data that was recorded for one year starting from December 1994 using an air pollution mobile monitoring station. The functional relationship between ozone level and the various independent variables has been determined by using a stepwise multiple regression modelling procedure. The model contains two terms that describe the dependence of ozone on nitrogen oxides (NOx) and nonmethane hydrocarbon precursor concentrations, and other terms that relate to wind direction, wind speed, sulphur dioxide (SO₂) and solar energy. In the model, the levels of the precursors are inversely related to ozone concentration, whereas SO₂ concentration, wind speed and solar radiation are positively correlated. Typically, 63 % of the variation in ozone levels can be explained by the levels of NOx. The model is shown to be statistically significant and model predictions and experimental observations are shown to be consistent. A detailed analysis of the ozone-temperature relationship is also presented; at temperatures less than 27 °C there is a positive correlation between temperature and ozone concentration whereas at temperatures greater than 27 °C a negative correlation is seen. This is the first time a non-monotonic relationship between ozone levels and temperature has been reported and discussed.