Modelling and Mapping Ozone Deposition in Europe

A new dry deposition module has been developed for European-scale mapping and modelling of ozone deposition fluxes (Emberson et al., 2000a,b). The module is being implemented in the photochemical long-range transport model of EMEP that is currently used to estimate exceedance of the existing critical levels for ozone within the UN ECE LRTAP programme. The deposition model evaluates the atmospheric, boundary layer and surface resistances to ozone transfer with the calculation of the dry deposition velocity performed according to a standard resistance formulation. The approach differs from other existing methods through the use of a detailed stomatal uptake model that describes stomatal conductance as a function of plant species, phenology and four environmental variables (air temperature, solar radiation, water vapour pressure deficit and soil moisture deficit). Comparison of preliminary model outputs for selected land-cover types indicate that the model is capable of predicting the seasonal and diurnal range in deposition velocities that have been reported previously in the literature. The application of this deposition scheme enables calculations of ambient ozone concentrations to be made using a biologically based method that can distinguish stomatal and non-stomatal components of total ozone deposition. The ability to estimate stomatal ozone fluxes (according to vegetation type, phenology and spatial location) that are consistent with evaluations of atmospheric ozone concentrations will be helpful in future assessments of ozone impacts to vegetation.     

Ozone measurements in jet airliner cabin air

Ozone measured in cabin air on 14 flights over polar areas shows maximum concentrations during Spring. Ozone numbers close to atmospheric values were found in the air entering the cabin through the air conditioning system but a reduction to about half of this value takes place immediately within the cabin air. Aircraft with recirculating cabin air showed an additional reduction by about 25%. Maximum concentrations are considerably higher and the duration of such periods longer than those reported in FAA Technical Report ADS-5 in which, however, data from polar areas during O₃ maximum are missing. Ozone destruction effects within the pressurization system as claimed in the FAA report are doubtful. Although O₃ reduction occurs within the cabin air, the threshold value of 0.1 ppm. for breathing air was surpassed in about 75 % of the flight time (8 to 10 hr between Copenhagen and Seattle) and maximum concentrations (0.4 ppm during 4 hr and 0.6 ppm during 1 hr) were found to be close to critical values recommended by the Environmental Protection Agency. Assuming that no O₃ destruction takes place in the pressurization system, O₃ concentrations exceeding 1 ppm, can be expected to enter the cabin at flight levels for commercial flight on polar routes during Spring. Some experiences during periods of high O₃ concentrations were increasing irritation in the eyes and the respiratory tract, effects different from those associated with low humidity in cabin air.     

Exceedance of EC Ozone Threshold Values in Europe in 1997

This paper summarises the annualinformation on ozone monitoring stations andexceedances of ozone threshold values during 1997transmitted by the Member States of the European Unionin the framework of Council Directive 92/72/EEC on airpollution by ozone. In August 1998 information for thecalendar year 1997 was received from all Member Statesand, on a voluntary basis, from 6 other Europeancountries (Switzerland, Czech Republic, Latvia,Norway, Poland and Slovakia).An evaluation of the exceedances and annual statisticsfor 1997 clearly shows that ozone is a severe,Pan-European problem. The threshold value set for theprotection of human health was exceeded substantiallyand in all reporting countries. The threshold value ofdaily average concentrations set for the protection ofvegetation was exceeded substantially (by up to afactor 3), widely (in all reporting countries) andfrequently (at several stations on more than 200days). The threshold value of hourly averageconcentrations set for the protection of vegetationwas exceeded largely and widely (reported by 10 EUMember States and in three out of the six otherEuropean countries) on a limited number of days.The threshold value for providing information to thepopulation was exceeded in 15 countries of which 12 EUMember States during a limited number of days.Exceedance of the threshold value for warning of thepopulation was reported from one station in Greece.     

Ozone - a Risk Factor for Trees and Forests in Europe?

Tropospheric ozone (O₃) may adversely affect tree growth, with critical levels for O₃ being exceeded in many parts of Europe. However, unequivocal evidence for O₃-induced foliar injury on woody species under field conditions has only been found in a few places. Visible O₃ injury appears to occur mainly in the Mediterranean Basin, which is also the area where the least amount of information is available on O₃ exposure as well as the sensitivity of individual species. Overall, the quantitative risk assessment of O₃ impacts on mature trees and forests is vague at the European scale, as most knowledge is derived from controlled O₃ fumigations of young trees, grown in isolation in exposure chambers. Research suggests that risks exist, but these need to be validated for stand conditions. O₃-induced changes in resource allocation rather than productivity appear to be crucial as they affect competitiveness and predisposition to parasite attack and may eventually lead to the loss of genetic diversity. ‘Free-air’ O₃ fumigations in forest canopies may reveal processes that are susceptible to O₃ stress under field conditions and provide a scientific basis towards quantitative risk assessment and realistic definitions of critical levels for O₃ in forest ecosystems.     

Modeling Dissolved Ozone and Bromate Ion Formation in Ozone Contactors

Many drinking water utilities that use source waters with significant bromide ion levels are currently seeking disinfection regimes that will minimize the formation of brominated disinfection byproducts while providing adequate disinfection. While ozonation appears to be a promising option for achieving these goals, the uncertainty of future drinking water regulations has developed a need for predicting actual disinfection byproduct formation prior to the costly investment for upgrading existing treatment facilities. The models developed in this paper provide comparisons of ozonation application methods, providing a basis for minimizing bromate and aiding in future design considerations. Theoretical and empirical models for the determination of ozone transferred, dissolved ozone concentrations, and bromate formation have been derived and compared with pilot-scale and full-scale data; a good agreement has been observed between the actual data and the predicted data, showing the validity of these models. True-batch bromate formation more closely simulated pilot-scale and full-scale data. Bromate formation in one stage vs two stage ozone contactors and different reactor configurations have been compared. Ozone gas phase concentration appears to have an effect on bromate formation as well.     

Yield Responses of Wheat to Ozone Exposure as Modified by Drought-Induced Differences in Ozone Uptake

Over a period of two years greenhouse experiments were carried out to quantify the interaction ozone exposure × water stress in winter wheat (Triticum aestivum L. cv. Perlo). Assessment of effects carried out on various yield parameters showed that abundant water supply made the plants most sensitive to ozone exposure. In well-watered plants (75%) of soil water capacity, s.w.c.), the AOT40 ozone exposure doses of 26.8 and 24.9 μmol mol^-1 hr^-1 (ppm.h) caused grain yield reductions by 35 and 39%. No reductions of yields were observed at severe water stress (35% of s.w.c.) condition. The decrease in ozone responsiveness under drought can be explained by a distinct reduction in ozone uptake (18 vs. 2 mmol m^-2 in well-watered vs. severely stressed plants at the same ozone exposure). The calculations of ozone uptake were based onrepeated measurements of leaf conductance. Generally curvi-linear regression functions explained the dependence of relative yield on ozone and on water stress better than multiple simple linear regression functions. The consideration of ozone uptake instead of ozone exposure improved the performances of the models further. For explaining grain yield, 96.8% of the variances could be explained by a model resulting from curvi-linear regression fitting. A suggestion for calculating correction factors to modify critical levels in the case of limited water supply is presented.     

Ozone sensitivity of plants in natural communities

Field fumigation studies conducted in grassland, oak, aspen, and conifer, communities established the injury threshold of prevalent plant species to ozone. Several important species, including Bromus tectorum, Quercus gambelii, and Populus tremuloides, were injured by a single 2-hours exposure to 15 pphm ozone. Over half the perennial forbs and woody species studied were visibly injured at concentrations of 30 pphm ozone or less. It is postulated that lower concentrations at prolonged or repeated exposures to ozone may impair growth and affect community vigour and stability. Continued exposure of natural plant communities to ozone is expected to initiate major shifts in the plant composition of communities.     

Conservation Agriculture in Europe

The adoption of Conservation Agriculture (CA) in Europe varies according to the ecological regions of the continent. Although Europe is behind other countries in adoption of CA, the indicators for future progress are encouraging. The area where CA is applied is growing rapidly because of increasing environmental awareness, including soil protection, and because of the need to reduce production costs. The European Conservation Agriculture Federation (ECAF) plays an important role in the adoption and dissemination of CA practices, and in discussions involving CA and the EU Common Agricultural Policy (CAP) reform.Yield performance and stability, operating costs, environmental policies and programs of the Common Agricultural Policy (CAP), and climate change will likely be the major driving forces defining the direction and for the extension of CA in Europe. The role of agriculture in climate change mitigation in the EU is discussed in the paper.     

Anthropogenic mercury emission in Europe

Preliminary estimates of Hg emissions from anthropogenic sources in Europe have been prepared to meet the request of air pollution transport modeling. Major emphasis was placed on four source categories: 1) combustion of fossil fuels, 2) non-ferrous metal production, 3) waste related sources, and 4) chlor-alkali production. Three chemical species: elemental, bivalent and particulate Hg were considered in these estimates. The emission estimates were spatially distributed within the EMEP grid of 150 km × 150 km for the year 1982.     

Calculating nitrogen deposition in Europe

Nitrogen deposition calculations for Europe were performed by separate models describing the long-range transport of ammonia and oxidized N. A linearized version of a non-linear atmospheric chemistry model was used for calculating oxidized N. Model computations were found to be consistent with the observed spatial pattern of wet nitrate deposition in Europe. Interannual meteorological variability was estimated to cause a typical year-to-year variation in annual oxidized N deposition of about 6 to 10%. Nitrogen deposition was computed for several NO _x emissions reduction scenarios. These scenarios were derived from an OECD study and applied to the 27 largest countries in Europe. Most reduction scenarios affected the deposition pattern of oxidized N, but the most extreme NO _x emission reduction scenario did not change very much the overall pattern of total (oxidized N plus ammonia N) N deposition. Depending on the desired level of environmental protection, it may be necessary to reduce ammonia emissions in addition to NO _x emissions in order to reduce N deposition in Europe.     

Ozone tolerance related to flavonol glycoside genes in soybean

Ozone toxicity can reduce soybean yields by an estimated 5 to 20%. The most economical and practical solution to the problem would be to use ozone‐tolerant cultivars. Because ozone toxicity is an oxidative stress, one would expect that plants having higher concentrations and proper kinds of antioxidants would be more tolerant. To test this hypothesis, 20 soybean lines or cultivars varying in contents of flavonol glycosides (naturally occurring antioxidants) were tested for ozone tolerance in a fumigation chamber and in phyto‐toxic concentrations of ozone in ambient, unfiltered, air in a greenhouse. In general, ozone tolerance was associated with the presence of kaempferol glycosides, particularly K3 through K6 and K9. Lines containing no kaempferol glycosides (OX942 & OX281) were among the most sensitive to ozone stress. The K9 compound has been associated with reduced numbers of stomata, drought tolerance, and slower growth rates, and this could reduce ozone absorption and toxicity, or K9 may be more effective in detoxifying ozone than other glycosides. Lee soybean was more tolerant to ozone and to manganese (Mn) toxicity (also an oxidative stress) than Forrest. Cross tolerances of plant genotypes to these two stresses deserve additional study. Among cultivars compared, Mukden was ozone tolerant, Columbia and Harosoy were sensitive, and Blackhawk was moderately sensitive.     

Mapping Ozone Critical Levels for Vegetation in Central Italy

Within the framework of the UN-ECE Convention on Long-Range Trans-boundary Air Pollution, critical ozone levels for forest trees and crops have been determined. This paper shows the mapping results of short and long-term threshold exceedances in an area of Central Italy. Eighty-thousand hourly mean ozone concentrations were recorded and computed to evaluate the potential distribution of the pollutant in the area. The results suggest that the threshold is frequently exceeded in the summer, and this may be very critical for the plants' health.     

臭氧杀灭循环营养液中三种土传病原菌的试验

为给臭氧应用于循环营养液消毒提供指导,该文研究了营养液中臭氧浓度的上升、衰减,臭氧杀灭营养液中3种植物病原菌所需的残余臭氧浓度、接触时间和残留臭氧对黄瓜根系的伤害。结果表明：高浓度臭氧气体在营养液中形成的臭氧平衡浓度高,达到平衡浓度所需的时间短;低浓度臭氧气体形成的臭氧平衡浓度低,达到平衡浓度需要的时间长。当营养液中残余臭氧浓度为0.6 mg/L,接触时间5 min时,臭氧对10³ cfu/mL浓度黄瓜枯萎病、番茄枯萎病和10⁶ cfu/mL浓度十字花科软腐病3     

Modeling of Stomatal Conductance for Estimating Ozone Uptake of Fagus crenata Under Experimentally Enhanced Free-air Ozone Exposure

We examined a performance of the multiplicative stomatal conductance model to estimate the stomatal ozone uptake for Fagus crenata. Parameterization of the model was carried out by in-situ measurements in a free-air ozone exposure experiment. The model performed fairly well under ambient conditions, with low ozone concentration. However, the model overestimated stomatal conductance under enhanced ozone condition due to ozone-induced stomatal closure. A revised model that included a parameter representing ozone-induced stomatal closure showed better estimation of ozone uptake. Neglecting ozone-induced stomatal closure induced a 20?% overestimation of the stomatal uptake of ozone. The ozone-induced stomatal closure was closely related to stomatal ozone uptake rather than accumulated concentrations of ozone exceeding 40?nmol mol^?1. Our results suggest that ozone-induced stomatal closure should be implemented to stomatal conductance model for estimating ozone uptake for F. crenata. The implementation will contribute to adequate risk assessments of ozone impacts on F. crenata forests in Japan.     

Passive Ozone Monitoring for Forest Health Assessment

Critical levels of tropospheric ozone, established for the protection of crops and other plants, are now reported as being exceeded over large forested areas, giving rise to the need for an extensive monitoring program to confirm ambient levels within the forest and to detect related forest health effects. The requirement for an inexpensive monitor that can be used in remote locations prompted the development of the Can Oxy Plate^TM passive ozone monitor and a monitoring protocol by the air pollution research group of the Canadian Forest Service, Forest Health Network. The monitors underwent initial trials in 1996 and operational trials during 1997 that involved two 2-3 week mid summer exposures in the canopy at selected forest health monitoring plots across Canada, and at adjacent forest openings. In both trials monitors were also co-located with the nearest instrumental ozone monitor. This allowed for the production of a field calibration for quality assurance assessment under field conditions. Results from 1996 indicate highly significant correlations with accumulated ambient ozone concentrations from the instrumental monitors at the co-located sites (r=0.88, p=0.0002). However, no such relationship was found between these sites and the forest plots which were up to 200 kilometres away. This may indicate spatial heterogeneity in ozone exposure between the continuous air quality monitoring sites and the forest plots. This information, together with our knowledge that strong gradients of ozone exposure are found within the canopy, underlines the importance of in situ monitoring of ozone exposure of forest health plots at risk to ozone effects.     

Soil vulnerability to pollution in Europe

Abstract. Pollution by inorganic and organic substances is increasingly disrupting the natural functions of soils. Some soils seem capable of receiving and holding chemical compounds, at the same time retaining their ecological flexibility, but others are readily damaged and should be regarded as vulnerable to particular pollution scenarios.
At the request of the Chemical Time Bombs (CTB) Project, the International Soil Reference and Information Centre (ISRIC) organized an international workshop to assess the feasibility of increasing awareness of 'soil vulnerability' by a mapping exercise for Europe (SOVEUR), at a scale of 1:5 M, with reference to selected organic and inorganic contaminants. The workshop participants outlined procedures for a GIS-based approach to determining areas where vulnerable soils occur, and formulated proposals for the implementation phase of the SOVEUR programme. Funding is now sought for continuation of the work outlined in this paper.     

Formation and Deposition of Ozone in a Red Pine Forest

Concentrations of ozone and nitrogen oxides, together with air temperature and solar radiation intensity, were measured at several heights on a tower standing through the canopy of a red pine forest in summer and in autumn. In the summer observation, the diurnal variation patterns of ozone concentration both above and below the canopy were all similar and parallel to the solar radiation intensity. Using the data collected immediately above the canopy, deviation from the Leighton relationship and variations of concentration sums [O₃] + [NO] and [NO₂] + [NO] were examined, and as a result, it was supposedthat ozone was photochemically formed there in the daytime, probably because hydrocarbons emitted from pine trees broke the photostationary state among ozone and nitrogen oxides. The vertical temperature profile exhibited an inversion at the leaf-layer, which must have hindered vertical mixing of the air and made the trunk space more or less isolated from the upper atmosphere. These observations led to an idea that the similarity of the ozone variation pattern at every height was caused by the photochemical formation that proceeded simultaneously above and below the canopy rather than by vertical transport. Such situations of ozone formation were supported by observation of two maximums in the ozone vertical profile, one immediately above the canopy and another in the trunk space. Another feature of the ozone profile was a deep minimum in the leaf layer, which indicated ozone deposition onto leaf surfaces. This study thus revealed concurrence of ozone formation and deposition, and left two potentially important implications worthy of further investigation: (1) a forest is not always a sink but can be a source of ozone in sunlit conditions, and (2) deposition of ozone to trees can take place not only from outside but also from inside of a forest. In the autumn observation, however, the ozone formation was barely recognizable above the canopy and no longer found in the trunk space; in addition, the ozone concentration minimum in the leaf layer disappeared, suggesting that the deposition or removal was dependent on temperature.     

Interaction Between Ozone Exposure and Iron Nutrition in Two Tobacco Cultivars

The initial objective was to confirm evidence, obtained from field grown plants, for iron (Fe) accumulation in leaves under ozone exposure. Tobacco plants were grown in pots under either open air or growth chamber conditions. The ozone-sensitive cultivar Bel W3 showed symptoms of ozone injury only when grown outside, while the cultivar Virginia never developed symptoms. In both cultivars, basal leaves of plants grown outside had higher concentration of Fe, but not of manganese (Mn) or zinc (Zn), than those from the growth chamber. Results suggest an interference of the oxidative stress with the mechanisms regulating Fe homeostasis. A second objective was to test whether differences in tolerance to ozone correspond with differences in tolerance to Fe toxicity. Iron toxicity was induced by supplying an excess of Fe-EDTA to plants, grown hydroponically in a growth chamber, upon partial root cutting. Symptoms in leaves were more severe in Bel W3 than in Virginia, which suggested that mechanisms of tolerance to ozone were also effective against Fe toxicity. In both cultivars, a good correlation was determined between Fe accumulation and ethylene production in the leaves.