Significant Ozone Research Articles

Variability of total ozone due to the NAO as represented in two different model systems

To explain regional trends and long time variability of ozone the understanding and quantie cation of dynamical mechanisms ine uencing the zonal asymmetry of ozone is essential. Therefore we assess here the relationship between total ozone variability and the North Atlantic Oscillation (NAO), one of the dominant modes of variability in the European sector using two different model systems in conjunction with the same simplie ed ozone chemistry. One model is the Met Ofe ce Unie ed Model, which is a comprehensive general circulation model forced by prescribed sea-surface temperatures only. The other model is the chemistry-transport model SLIMCAT, which is driven by meteorological observations and therefore includes observed meteorological trends. The simplie ed ozone chemistry is based on the Cariolle scheme with an additional parameterization of polar ozone loss, but with no allowance for changing chlorine or aerosol levels. It is shown that the NAO signal in ozone during mid-winter is well represented in both model systems. Geopotential height correlations are used to explain the spatial pattern. It is demonstrated that composites of total ozone derived from the model integrations are capable of capturing the observed spatial characteristics as seen in TOMS data. Implications are drawn for NAO induced long time variability/regional trends of ozone. Zusammenfassung

The Influence of Large-Scale Eddy Flux Variability on the Zonal Mean Ozone Distribution

The influence of the variability of large-scale eddy heat and momentum fluxes on interannual and decadal changes in the zonal mean ozone distribution is investigated based on a two-dimensional circulation model with interactively coupled transport and chemistry. The large-scale eddy fluxes are prescribed according to observations, that is, in terms of monthly mean eddy mixing coefficients that are derived from ECMWF reanalysis 1979–93 (ERA-15). The results show that the eddy-forced changes in the lower-stratospheric residual circulation and eddy mixing processes induce coherent changes in temperature, ozone, and other chemical tracers. Significant ozone declines are found mainly in the lower stratosphere during winter, with maximum values of about −1.2 Dobson units (DU) per kilometer per decade at midlatitudes and more than −2 DU km−1 decade−1 at polar latitudes. The seasonal and vertical structure of the observed Northern Hemispheric ozone trend is captured in a remarkable way. It is also shown that, at midlatitudes, maximum declines in the zonal mean lower-stratospheric ozone are mainly related to the eddy mixing processes, and, at polar latitudes, to the induced changes in the lower-stratospheric temperatures.

Effect of stratosphere‐troposphere exchange on the future tropospheric ozone trend

This paper investigates the impact of circulation changes in a changed climate on the exchange of ozone between the stratosphere and the troposphere. We have identified an increase in the net transport of ozone into the troposphere in the future climate of 37%, although a decreased ozone lifetime means that the overall tropospheric burden decreases. There are regions in the midlatitudes to high latitudes where surface ozone is predicted to increase in the spring. However, these increases are not significant. Significant ozone increases are predicted in regions of the upper troposphere. The general increase in the stratospheric contribution (O3s tracer) to tropospheric ozone in the climate changed scenario indicates that the stratosphere will play an even more significant role in the future.

Variability of ozone loss during Arctic winter (1991–2000) estimated from UARS Microwave Limb Sounder measurements

A comprehensive analysis of version 5 (V5) Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) ozone data using a Lagrangian transport (LT) model provides estimates of chemical ozone depletion for the 1991–1992 through 1997–1998 Arctic winters. These new estimates give a consistent, three‐dimensional picture of ozone loss during seven Arctic winters; previous Arctic ozone loss estimates from MLS were based on various earlier data versions and were done only for late winter and only for a subset of the years observed by MLS. We find large interannual variability in the amount, timing, and patterns of ozone depletion and in the degree to which chemical loss is masked by dynamical processes. Analyses of long‐lived trace gas data suggest that the LT model sometimes overestimates descent at levels above ∼520 K, so we have most confidence in the results at lower levels. When the vortex is shifted off the pole and the cold region is near the vortex edge (e.g., late winter 1993 and 1996), most rapid ozone depletion occurs near the vortex edge; when the vortex and cold region are pole‐centered (e.g., late winter 1994 and 1997), most ozone loss takes place in the vortex core. MLS observed the most severe ozone depletion in 1995–1996, with about 1.3 ppmv cumulative loss for the winter at 465 K by 3 March 1996; ∼1.0 ppmv cumulative loss is seen at 465 K by mid‐March 1993. Analyses of MLS data show significant ozone loss during January in most years, ranging from ∼0.3 to 0.6 ppmv at 465 K. A modified LT model used with the limited MLS data in 2000 gives rough estimates of ∼0.04 and 0.006–0.012 ppmv/day during 2–12 February and 12 February–29 March 2000, respectively, broadly consistent with other studies of the 1999–2000 winter. Estimates of depletion in MLS column ozone above 100 hPa are considerably smaller than other reported column loss estimates, primarily because many estimates include loss below 100 hPa and because MLS does not continuously observe the Arctic after early spring. Our results from analyses of MLS data confirm previous conclusions of broad overall agreement between many ozone loss estimates in the Arctic lower stratosphere near 450–480 K.

Evidence for the production of trioxygen species during antibody-catalyzed chemical modification of antigens.

Recent work in our laboratory showed that products formed by the antibody-catalyzed water-oxidation pathway can kill bacteria. Dihydrogen peroxide, the end product of this pathway, was found to be necessary, but not sufficient, for the observed efficiency of bacterial killing. The search for further bactericidal agents that might be formed along the pathway led to the recognition of an oxidant that, in its interaction with chemical probes, showed the chemical signature of ozone. Here we report that the antibody-catalyzed water-oxidation process is capable of regioselectively converting antibody-bound benzoic acid into para-hydroxy benzoic acid as well as regioselectively hydroxylating the 4-position of the phenyl ring of a single tryptophan residue located in the antibody molecule. We view the occurrence of these highly selective chemical reactions as evidence for the formation of a short-lived hydroxylating radical species within the antibody molecule. In line with our previously presented hypothesis according to which the singlet-oxygen ((1)O*(2)) induced antibody-catalyzed water-oxidation pathways proceeds via the formation of dihydrogen trioxide (H(2)O(3)), we now consider the possibility that the hydroxylating species might be the hydrotrioxy radical HO(3)*, and we point to the remarkable potential of this either H(2)O(3)- or O(3)-derivable species to act as a masked hydroxyl radical HO* in a biological environment.

Environmental ozone effects in different population subgroups

The study objective was to get more information on characteristics of ozone risk groups. We performed repeated (on average 16 times) lung function tests and interviews with 171 persons belonging to four different population subgroups (44 healthy children, 43 juvenile asthmatics, 43 athletes, and 41 elderly).The environmental half hour mean ozone concentrations ranged from 8 to 99 ppb. For two groups there was significant NO2 co-pollution. The asthmatics showed statistically significant ozone related increased ORs for eye irritations, the elderly for nose irritations. Significant lung function decrements (increase in ozone by 50 ppb) were found for asthmatics (FVC −4.3% afternoon one day lag, −4.9% afternoon two day lag, −3.6% morning one day lag) and children (FVC −3.2% same morning, PEF −11.9% same morning, PEF −4.6% morning one day lag). In the group of elderly, however, there were also some significant FVC and PEF increments. Ozone responders were found more often in the groups of asthmatics and children (21% resp. 18%) compared with elderly and athletes (both 5%). The results suggest that children and asthmatics have a higher risk of being ozone sensitive showing more ozone related acute lung function decrements than other population groups.

Assessment of SAGE version 6.1 ozone data quality

The Stratospheric Aerosol and Gas Experiment (SAGE) II V6.1 ozone retrievals are shown to be of better precision at all levels and to be much more accurate than previous retrievals in the lower stratosphere below 20 km altitude. A filtering procedure for removing anomalous ozone profiles associated with volcanic aerosol/cloud effects and other identified artifacts in V6.1 ozone is described. The agreement between SAGE and ozonesondes in the mean is shown to be approximately 10% down to the tropopause. Relative to the sondes, SAGE tends to slightly overestimate ozone (less than 5%) between 15 and 20 km altitude and systematically underestimates ozone in the troposphere by approximately 30% in the regions between 8 km altitude and 2 km below the tropopause. The precisions (random errors) of SAGE ozone retrievals above 25 km altitude are estimated to be 4% or better; they are a factor of 10 worse below 16 km altitude. Linear trends in the differences between coincident SAGE and ozonesondes measurement are generally less than 0.3%/yr and not significantly different from zero in 95% confidence intervals. Compared to V5.96 retrievals, ozone trend differences between 20 and 50 km altitude are approximately 0.1%/yr; below 20 km altitude the SAGE II trends are more positive by approximately 0.2%/yr. For the 1984–1999 period, the SAGE II shows a localized ozone loss of −0.4 ± 0.25%/yr (2σ) in the tropics at 20 km altitude. In the lower stratosphere, between 16 and 22 km altitudes, the SAGE shows significant ozone losses in the midlatitudes in both hemispheres during the 1979–1999 periods. The ozone trends range from −0.24 ± 0.18%/yr to −0.77 ± 0.46%/yr (2σ). However, in the 1984–1999 period, the downward trends are smaller (−0.07%/yr to −0.25%/yr) in this altitude range, and the trends in the integrated column from 12 to 17 km altitude in midlatitudes (35°–60°) are not significantly different from zero (0.1 ± 0.6%/yr (2σ)). Averaged over the tropics (20°S–20°N), the ozone column above 15 km altitude exhibit a trend of −0.12 ± 0.08%/yr (2σ).

A search for an anticorrelation between H2O and O3 in the lower mesosphere

We have looked for the expected anticorrelation between H2O and O3 in the lower mesosphere using data from HALOE and a simple one‐dimensional photochemical model. We use the fractional difference between the model and the data (ΔO3/O3) as a measure of the goodness of the fit of the model to the data. The model is run for each of over 1000 days of HALOE measurements from 30° S–30° N and from 1992–1999. Despite the 10% changes in upper stratospheric H2O which were observed during this period, we detect no significant ozone change in response to this H2O variability. Indeed, in the 2.0–0.4 mb region, the model error is lower when the water vapor is arbitrarily assumed to be invariant. Further, when H2O variability is considered, (ΔO3/O3) anticorrelates with H2O but not the temperature and solar flux. From this we conclude that the temperature and solar flux dependence are fairly well modeled and that the model error is due to the representation of the ozone dependence upon H2O in the model. Our results suggest that ozone near the stratopause is surprisingly insensitive to variations in H2O. If true, this insensitivity may make easier the observation of ozone recovery in the upper stratosphere due to declining chlorine. This result should also be considered when assessing the response of upper stratospheric ozone to increases in stratospheric humidity.

Ozone depletion observed by the Airborne Submillimeter Radiometer (ASUR) during the Arctic winter 1999/2000

In the winter 1999/2000 the Airborne Submillimeter Radiometer (ASUR) participated in the Stratospheric Aerosol and Gas Experiment III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone project on board the NASA research aircraft DC‐8. During three deployments in early December 1999, late January, and early March 2000, the ASUR instrument took various measurements of ozone and key species related to stratospheric ozone chemistry. After the sunlight reached the vortex region in January 2000 peak values of about 1.8 ppb ClO were measured by ASUR. There was nearly no ozone destruction observed during the period between mid December 1999 and late January 2000. As expected from ASUR observation of high chlorine activation and continuously low temperatures until mid March, significant ozone depletion was observed between late January and mid March 2000. In order to determine ozone loss it is important to separate dynamical and chemical effects. Since N2O is a good tracer due to its chemical stability in the lower stratosphere for determining ozone changes due to descent of air, ozone loss can be estimated from simultaneous measurements of ozone and N2O by ASUR. Between mid December 1999 and mid March 2000 a chemical ozone loss of about 30% (eq 1.1 ppm) in the altitude range between 19.0 and 22.2 km and of about 40% (eq 1.15 ppm) between 16.0 and 18.1 km was observed. The air masses subsided 2.1–3.2 km in the lower stratosphere due to diabatic descent in the period from mid December 1999 to mid March 2000 as derived from ASUR N2O measurements. Vortex‐averaged ASUR measurements of ozone are systematical greater than results from the Global Ozone Monitoring Experiment (GOME) which has a similar vertical resolution than ASUR. This, however, has little impact on the determination of delta ozone and chemical loss estimates.

Annual ozone deposition to a Sierra Nevada ponderosa pine plantation

Ozone concentration and ecosystem scale fluxes were measured continuously from June 1999 to June 2000 above a ponderosa pine plantation at Blodgett Forest, an Ameriflux site located ∼75 km northeast of Sacramento, CA (1300 m). The ponderosa pine trees were most active during the summer but maintained a low level of activity during the fall, winter, and spring. Cumulative ozone flux for the year was 127 mmol m −2 with the contribution for each season being 37% for summer, 18% for fall, 15% for winter, and 30% for spring. The high levels of cumulative ozone deposition over non-summer seasons indicate that significant ozone damage may occur during times when ozone concentrations are not at their maximum. Ozone flux is dependent upon both ozone deposition velocity (O 3 V d, how effective the ecosystem is at taking up ozone) and ambient ozone concentration but was found to be more closely related to O 3 V d than to ozone concentration. The relationships between O 3 V d (and therefore ozone flux) and the controlling climatic variables were dynamic over the year, changing mainly with water status and phenology. Understanding how the relationship between ozone deposition and its driving variables interact and change over the year is therefore critical to understanding potential ozone damage to vegetated ecosystems. Additionally, we found that commonly used ozone exposure metrics such as SUM0 (sum of all ozone exposure during the day) were poor predictors of ozone uptake (flux) unless periods of ecosystem stress, such as drought, were excluded.

Quantification of source region influences on the ozone burden

A project was performed to quantify different influences on the ozone burden. It could be shown that large-scale meteorological influences determine a very large percentage of the ozone concentration. Local measures intended to reduce peak ozone concentrations in summer turn out to be not very effective as a result. The aim of this paper is to quantify regional emission influences on the ozone burden. The investigation of these influences is possible by comparison of the ozone (O 3) and oxidant (O x =O 3+NO 2) concentrations at high-elevation sites downwind and upwind of a source region by using back trajectories. It has been shown that a separation between large-scale influenced meteorological and regional ozone burdens at these sites is possible. This method is applied for an important emission area in Germany—the Ruhrgebiet. On average, no significant ozone contribution of this area to the regional ozone concentration could be found. A large part of the ozone concentration is highly correlated with synoptic weather systems, which exhibit a dominant influence on the local ozone concentrations. Significant contributions of related photochemical ozone formation of the source area of 13–15% have been found only during favourable meteorological situations, identified by the hourly maximum day temperature being above 25°C. This is important with respect to the EU daughter directive to EU 96/62/EC (Official Journal L296 (1996) 55) because Member States should explore the possibilities of local measures to avoid the exceedance of threshold values and, if effective local measures exist, to implement them.

Seasonal fluctuation of DNA photodamage in marine plankton assemblages at Palmer Station, Antarctica.

Ultraviolet radiation-induced DNA damage frequencies were measured in DNA dosimeters and natural plankton communities during the austral spring at Palmer Station, Antarctica, during the 1999-2000 field season. We found that the fluence of solar ultraviolet-B radiation (UV-B) at the earth's surface correlated with stratospheric ozone concentrations, with significant ozone depletion observed because of "ozone hole" conditions. To verify the interdependence of ozone depletion and DNA damage in natural microbial communities, seawater was collected daily or weekly from Arthur Harbor at Palmer Station, Antarctica, throughout "ozone season," exposed to ambient sunlight between 0600 and 1800 h and fractionated using membrane filtration to separate phytoplankton and bacterioplankton populations. DNA from these fractions was isolated and DNA damage measured using radioimmunoassay. Under low-ozone conditions cyclobutane dimer concentrations in bacterioplankton and phytoplankton communities were maximal. DNA damage measured in dosimeters correlated closely with ozone concentrations and UV-B fluence. Our studies offer further support to the theory that stratospheric deozonation is detrimental to marine planktonic organisms in the Southern Ocean.

Long-term ozone trends in Northern mid-latitudes with special emphasis on the contribution of changes in dynamics

Monitoring indicates that stratospheric ozone strongly decreased in the polar regions, most seriously over the Antarctica. It is widely accepted that polar ozone loss is caused by heterogeneous processes activating halogen radicals which originate from the man-made release of ozone depleting substances. Significant ozone decrease peaking in winter/spring also has been observed in mid-latitudes. It started around the beginning of the 1970s. In this paper we review recent studies which indicate that not only long-term trends in chemical composition but also long-term changes in the dynamical structure of the atmosphere have significantly contributed to the ozone decrease over mid-latitudes. Such changes most strongly affected the ozone shield in the lower stratosphere and over Europe. However, they also influence ozone over the entire extra-tropical Northern hemisphere.

Long-term ozone and UV variations at Thessaloniki, Greece

Total columnar ozone has been decreasing over middle latitudes (20°–60°) between 1979 and December 2000 at rates of about 4% in winter/spring and about 2% per decade in the summer. Total ozone trends through 1997 and through 2000 differ only over the middle and high latitudes of the northern hemisphere. This long-term trend was interrupted by periods of enhanced volcanic activity, which resulted to significant ozone losses (more than 5% per year) following large volcanic eruptions (El Chichon in 1982 and particularly Mt Pinatubo in 1991). Linked to the ozone decrease are well-documented global increases of the harmful UV-B solar radiation levels reaching ground level. Through 1997 the erythemal dose over middle latitudes in clear skies was increasing at rates exceeding 5% per decade while the solar UV irradiance at the lower wavelengths was increasing by more than 10% per decade, partly enhanced by the decrease of air pollutants such as sulfur dioxide in the case of Thessaloniki. However, evidence is presented in this study that during the last decade (1990–2001) over Thessaloniki, the ozone trend was smaller the order of −1.5% per decade. Also the associated increasing trends in the erythemal dose and at 305 nm are smaller not exceeding +2% and +4% per decade respectively under clear skies. The long-term UV variability has a QBO component, which cannot be overlooked, even in comparison with the amplitude of the annual cycle.

The global signal of the 11-year solar cycle in the stratosphere: observations and models

Earlier studies used the data from four solar cycles, to examine the global structure of the signal of the 11-year sunspot cycle (SSC) in the stratosphere and troposphere, using correlations between the solar cycle and heights and temperatures at different pressure levels. Here, this work is expanded in Part I to show the differences of geopotential heights and temperatures between maxima and minima of the SSC. This study puts the earlier work on a firmer ground and gives quantitative values for comparisons with models. In Part II, two general circulation models (GCMs) with coupled stratospheric chemistry are used to simulate the impact of changes in solar output. This paper is not intended as a review of the whole topic of solar impacts, but provides some results recently obtained in observations and modelling. Comparisons between the GCM results and observations show that the differences between solar maximum and solar minimum for temperature and ozone are generally smaller than observed. In the middle and upper stratosphere, models are closer to agreeing with observations of temperature, but a significant observed temperature difference near 100 hPa is not reproduced in the models. Also, model predictions of the shape of the vertical profile of the ozone difference do not agree with observations and the comparisons are hindered by large statistical uncertainties in both models and observations. Nonetheless, the results are an improvement on 2-D model results in showing a larger ozone signal in the lower stratosphere.

Allowing for solar forcing in the detection of human influence on tropospheric temperatures

Previous workers have used the radiosonde record of atmospheric vertical temperature structure to detect anthropogenic influence on climate [e.g. Santer et al., 1996a]. However, none of these studies explicitly considered the influence of natural forcing factors. Whilst decadal changes of radiative solar activity are small, they could be amplified by various mechanisms (e.g. Haigh, 1996), potentially accounting for a significant fraction of the observed signal. Gillett et al. [2000] show that the diagnostics used to detect anthropogenic influence on atmospheric temperature structure are strongly influenced by solar forcing. Here we repeat the analysis of Allen and Tett, [1999] (AT99) including a model‐simulated solar signal, to assess whether the observed tropospheric warming might be explained by solar forcing and the observed stratospheric cooling by the effects of ozone depletion. It transpires that previously reported results are robust to the inclusion of solar forcing since the greenhouse gas response is detectable even in the presence of solar forcing and stratospheric ozone depletion, allowing for an arbitrary amplitude of both solar and ozone signals.

Arctic ozone loss in threshold conditions: Match observations in 1997/1998 and 1998/1999

Chemical ozone loss rates inside the Arctic polar vortex were determined in early 1998 and early 1999 by using the Match technique based on coordinated ozonesonde measurements. These two winters provide the only opportunities in recent years to investigate chemical ozone loss in a warm Arctic vortex under threshold conditions, i.e., where the preconditions for chlorine activation, and hence ozone destruction, only occurred occasionally. In 1998, results were obtained in January and February between 410 and 520 K. The overall ozone loss was observed to be largely insignificant, with the exception of late February, when those air parcels exposed to temperatures below 195 K were affected by chemical ozone loss. In 1999, results are confined to the 475 K isentropic level, where no significant ozone loss was observed. Average temperatures were some 8°–10° higher than those in 1995, 1996, and 1997, when substantial chemical ozone loss occurred. The results underline the strong dependence of the chemical ozone loss on the stratospheric temperatures. This study shows that enhanced chlorine alone does not provide a sufficient condition for ozone loss. The evolution of stratospheric temperatures over the next decade will be the determining factor for the amount of wintertime chemical ozone loss in the Arctic stratosphere.

ENSO signal in total ozone over Tibet

From data analysis of ozone satellite observation and general circulation, this article discusses the seasonal and interannual variations of total ozone over Tibet. Analysis has been done on Quasi—Biennial Oscillation (QBO) in interannual ozone variation over Tibet, in comparison with QBO over the tropics and non—mountain region at the same latitudes of Tibet. The fact is shown that Tibet ozone QBO has an aver-aged period of 29 months, with an averaged amplitude of 8 DU. The Tibet ozone QBO is antiphase to the stratospheric wind QBO over the tropics, i.e., when the tropics 30 hPa—wind is easterly, ozone has a surplus, and vice verse. This article also discusses the impact of atmospheric transfer on ozone QBO over Tibet.

Estimating relationships between air mass origin and chemical composition

Observations of a chemical at a point in the atmosphere typically show sudden transitions between episodes of high and low concentration. Often these are associated with a rapid change in the origin of air arriving at the site. Lagrangian chemical models riding along trajectories can reproduce such transitions, but small timing errors from trajectory phase errors dramatically reduce the correlation between modeled concentrations and observations. Here the origin averaging technique is introduced to obtain maps of average concentration as a function of air mass origin for the East Atlantic Summer Experiment 1996 (EASE96, a ground‐based chemistry campaign). These maps are used to construct origin averaged time series which enable comparison between a chemistry model and observations with phase errors factored out. The amount of the observed signal explained by trajectory changes can be quantified, as can the systematic model errors as a function of air mass origin. The Cambridge Tropospheric Trajectory model of Chemistry and Transport (CiTTyCAT) can account for over 70% of the observed ozone signal variance during EASE96 when phase errors are side‐stepped by origin averaging. The dramatic increase in correlation (from 23% without averaging) cannot be achieved by time averaging. The success of the model is attributed to the strong relationship between changes in ozone along trajectories and their origin and its ability to simulate those changes. The model performs less well for longer‐lived chemical constituents because the initial conditions 5 days before arrival are insufficiently well known.

Uncertainty in preindustrial abundance of tropospheric ozone: Implications for radiative forcing calculations

Recent model calculations of the global mean radiative forcing from tropospheric ozone since preindustrial times fall in a relatively narrow range, from 0.3 to 0.5 W m−2. These calculations use preindustrial ozone fields that overestimate observations available from the turn of the nineteenth century. Although there may be calibration problems with the observations, uncertainties in model estimates of preindustrial natural emissions must also be considered. We show that a global three‐dimensional model of tropospheric chemistry with reduced NOx emissions from lightning (1–2 Tg N yr−1) and soils (2 Tg N yr−1) and increased emissions of biogenic hydrocarbons can better reproduce the nineteenth century observations. The resulting global mean radiative forcing from tropospheric ozone since preindustrial times is 0.72–0.80 W m−2, amounting to about half of the estimated CO2 forcing. Reduction in the preindustrial lightning source accounts for two thirds of the increase in the ozone forcing. Because there is near‐total titration of OH by isoprene in the continental boundary layer of the preindustrial atmosphere, isoprene and other biogenic hydrocarbons represent significant ozone sinks. The weak or absent spring maximum in the nineteenth century observations of ozone is difficult to explain within our understanding of the natural ozone budget. Our results indicate that the uncertainty in computing radiative forcing from tropospheric ozone since preindustrial times is larger than is usually acknowledged.