Background ozone monitoring and phytodetection in the greater rural area of Corinth--Greece

Natural background ozone levels were monitored in three places within the greater rural area of Corinth, namely Bogdani Hill, Astronomical Observatory of Krionerion, and Kiato, and compared with ambient ozone monitored in the metropolitan area of Athens. Measurements were made sequentially, for a few weeks at each place, during the summer of 2000. In addition, ozone phytodetection, using tobacco (Nicotiana tabacum L.) plants of the Bel-W3 and Zichnomirodata varieties, was conducted in 12 places (the above included). Moreover, stomatal conductance was measured in the Bel-W3 plants, as well as in leaves of cultivated grape-vines (Vitis vinifera L.) and in needles of Aleppo pine (Pinus halepensis Mill.) trees and compared with the diurnal pattern of ozone concentrations.The 24 and 12 (08:00-20:00) hourly averages of ozone concentrations were high in Athens (37; 51 ppb), at Bogdani Hill (53; 56 ppb) and at the Astronomical Observatory (56; 55 ppb), but relatively low in Kiato (30; 34 ppb). Furthermore, the average daily AOT40 (accumulated exposure over 40 ppb for the daylight hours) (ppbh) was 193 in Athens, 212 at Bogdani Hill, 192 at the Astronomical Observatory and 47 in Kiato. Ozone concentrations exhibited the usual diurnal pattern in Athens (altitude 50 m), where they were maximum during midday and early afternoon hours, as well as at Bogdani Hill (300 m) and in Kiato (5 m) where, however, they were maximal 1-3 h later. At the Astronomical Observatory (altitude 920 m) ozone remained constant during both daylight and night hours. The differences in diurnal patterns are consistent with those in places of different elevation, reported elsewhere.The Bel-W3 plants were injured at all 12 places; Zichnomirodata plants exhibited lower injury and only in some of the places; probable ozone symptoms were also observed on vine plants and pine trees. The greatest injury was observed at the high altitude places of Astronomical Observatory and Mougostos. Stomatal conductance, in all three species, peaked during morning and early midday hours when ozone levels were higher in the high altitude, and lower in the low altitude, places.     

Photochemical air pollutant levels and ozone phytotoxicity in the region of Mesogia–Attica, Greece

The levels of photochemical air pollutants: O₃, NO and NO₂, were monitored in Athens and in the neighbouring region of the Mesogia plain (Spata, Artemis and Markopoulo) from 1 May–31 August 2000. Phytodetection of ozone was also conducted using bioindicator plants of Bel-W3 and Zichnomirodata (KK6/5) tobacco varieties. The average maximum daily O3 concentration was 60–75 ppb, while the 24 hour average ranged from 40–65 ppb. The AOT40 (ppb hours) index was very high in Athens (16 679 over 121 days), Spata (16 325 over 110 days), Artemis (8093 over 22 days) and Markopoulo (18 646 over 113 days), suggesting potentially phytotoxic ozone levels. The ozone bioindicator plants of Bel-W3 and KK6/5 tobacco varieties were highly injured in all regions confirming the phytotoxicity of those ozone levels. The levels of NO and NO₂ recorded at the three stations, in the Mesogia plain, were considerably lower than those occurring in Athens. The data presented here provide important background information concerning pollution levels in the Mesogia plain shortly before the operation of the new international airport 'Eleftherios Venizelos' in this region (March 2001).     

Using plant biomonitors and flux modelling to develop O3 dose-response relationships in Catalonia

We used tobacco Bel-W3 biomonitoring data and ozone flux modelling (WINDEP model) with the aim of developing the absorbed dose-response relationship, and comparing this approach with the most commonly used AOT40 (the sum of hourly ozone concentrations above a cut-off of 40 ppb during daylight hours, when global radiation exceeds 50 W m(-2)) in the estimation of exposure-damage curves. Leaf damage values were more related to OAD(15 days, potential) (potential ozone absorbed dose calculated over 15 consecutive days) than to AOT40 in all the studied stations. An OAD(15 days, potential) of 180 mg m(-2) was found to be the threshold for damage to the most sensitive species in this region under well watered conditions. The results show the applicability of the flux approach for risk assessment at the local scale, the improvement of the ozone damage estimation when the potential absorbed dose is modelled and used instead of just the ozone exposure, and finally, the possibilities opened by the use of biomonitoring networks.     

Ozone exposure thresholds and foliar injury on forest plants in Switzerland

Canton Ticino in southern Switzerland is exposed to some of the highest concentrations of tropospheric ozone in Europe. During recent field surveys in Canton Ticino, foliar symptoms identical to those caused by ozone have been documented on native tree and shrub species. In Europe, the critical ozone level for forest trees has been defined at an AOT40 of 10 ppm.h O3 (10 ppm.h accumulated exposure of ozone over a threshold of 40 ppb) during daylight hours over a six-month growing season. The objective of this study was to determine the amount of ambient ozone required to induce visible foliar symptoms on various forest plant species in southern Switzerland. Species were grown within eight open-top chambers and four open plots at the Vivaio Lattecaldo Cantonal Forest Nursery in Ticino, Switzerland. Species differed significantly in terms of the ppb.h exposures needed to cause visible symptoms. The most to least symptomatic species grown within open-plots in this study rank as Prunus serotina, Salix viminalis, Vibrnum lantana, Rhamnus cathartica, Betula pendula, Rumex obtusifolius, Sambucus racemosa, Morus nigra, Prunus avium, Fraxinus excelsior, Rhamnus frangula, Alnus viridis, Fagus sylvatica and Acer pseudoplatanus. Similar rankings were obtained in the non-filtered chamber plots. The ranking of species sensitivity closely follows AOT values for the occurrence of initial symptoms and symptom progression across the remainder of the exposure season. Species that first showed evidence of foliar injury also demonstrated the most sensitivity throughout the growing season, with symptoms rapidly advancing over ca. 25-30% of the total plant leaf surfaces by the end of the observation period. Conversely, those species that developed symptoms later in the season had far less total injury to plant foliage by the end of the observation period (1.5 to < 5% total leaf area injured). The current European ambient ozone standard may be insufficient to protect native plant species from visible foliar injury, and many more native species may be sensitive to ozone-induced foliar injury than are currently known.     

Effects of ozone on chlorophyll and quantum yield of tobacco (Nicotiana tabacum L.) varieties

Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.     

Effects of ozone on chlorophyll and quantum yield of tobacco (Nicotiana tabacum L.) varieties

Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.     

Suitability of Nicotiana tabacum 'Bel W3' for biomonitoring ozone in São Paulo, Brazil

Nicotiana tabacum 'Bel W3' is a widely used sensitive bioindicator for ambient ozone, but it is rarely used in tropical countries. Our goal was to determine the suitability of this plant for biomonitoring ozone in the city of S?o Paulo by evaluating the relationships between leaf necroses and ozone under field conditions and measurements of chlorophyll a fluorescence and antioxidants in plants exposed to different concentrations of ozone in closed chambers. While a weak linear relationship between leaf injury and ozone concentrations (R(2)=0.10) was determined in the field, a strong linear relationship was observed in the chamber experiments. Maximum leaf injury was observed in plants submitted to 40 ppb, which coincided with a significant decrease in fluorescence and total ascorbic acid. The relationship between leaf damage observed in the field and ozone was improved when the concentrations were limited to 40 ppb (R(2)=0.28).     

A synthesis of AOT40-based response functions and critical levels of ozone for agricultural and horticultural crops

Crop-response data from over 700 published papers and conference proceedings have been analysed with the aim of establishing ozone dose-response functions for a wide range of European agricultural and horticultural crops. Data that met rigorous selection criteria (e.g. field-based, ozone concentrations within European range, full season exposure period) were used to derive AOT40-yield response functions for 19 crops by first converting the published ozone concentration data into AOT40 (AOT40 is the hourly mean ozone concentration accumulated over a threshold ozone concentration of 40 ppb during daylight hours, units ppm h). For any individual crop, there were no significant differences in the linear response functions derived for experiments conducted in the USA or Europe, or for individual cultivars. Three statistically independent groups were identified: ozone sensitive crops (wheat, water melon, pulses, cotton, turnip, tomato, onion, soybean and lettuce); moderately sensitive crops (sugar beet, potato, oilseed rape, tobacco, rice, maize, grape and broccoli) and ozone resistant (barley and fruit represented by plum and strawberry). Critical levels of a 3 month AOT40 of 3 ppm h and a 3.5 month AOT40 of 6 ppm h were derived from the functions for wheat and tomato, respectively.     

Integrated biomonitoring of air quality with plants and lichens: a case study on ambient ozone from central Italy

A biennial integrated survey, based on the use of vascular plants for the bioindication of the effects of tropospheric ozone together with the use of automatic analysers of ozone, as well as the mapping of lichen biodiversity was performed in the area of Castelfiorentino (Tuscany, central Italy). Photochemically produced ozone proved to be a fundamental presence during the warm season, with maximum hourly means reaching 114 ppb, exceeding the information threshold as fixed by EU: the use of supersensitive tobacco Bel-W3 confirmed the opportunity of carrying out detailed cost-effective monitoring surveys. The potential for didactical and educational implications of this methodology are appealing. Critical levels set up for the protection of vegetation have exceeded considerably. The comparison of biomass productivity in sensitive and resistant individuals (NC-S and NC-R white clover clones, in the framework of an European network) provided evidence that ambient ozone levels are associated with relevant reduction (up to 30%) in the performance of sensitive material; effects on flowering were also pronounced. The economic assessment of such an impact deserves attention. Mapping of epiphytic lichen biodiversity – which has been used to monitor air quality worldwide – was not related to ozone geographical distribution as depicted by tobacco response.     

Tibouchina pulchra (Cham.) Cogn., a native Atlantic Forest species, as a bio-indicator of ozone: visible injury

Tibouchina pulchra saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF) and ambient non-filtered air+40 ppb ozone (NF+O3) 8 h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12,895 ppb h(-1), respectively, for the three treatments. After 25 days of exposure (AOT40=3871 ppb h(-1)), interveinal red stippling appeared in plants in the NF+O3 chamber. In the NF chamber, symptoms were observed only after 60 days of exposure (AOT40=910 ppb h(-1)). After 60 days, injured leaves per plant corresponded to 19% in NF+O3 and 1% in the NF treatment; and the average leaf area injured was 7% within the NF+O3 and 0.2% within the NF treatment. The extent of leaf area injured (leaf injury index) was mostly explained by the accumulated exposure of ozone (r2=0.89; p<0.05).     

Effects of ozone exposure in open-top chambers on poplar (Populus nigra) and beech (Fagus sylvatica): a comparison

Rooted cuttings of poplar (Populus nigra) and seedlings of beech (Fagus sylvatica) were exposed to ozone in open-top chambers for one growing season. Three treatments were applied: charcoal-filtered (CF), non-filtered (NF) and non-filtered air plus 30 ppb (nl l(-1)) ozone (NF+). Extra ozone was only added on clear days, from 09:00 until 17:00-20:00. The AOT40s (accumulated exposure over a threshold of 40 ppb), calculated from April to September were 4055 ppb.h for the NF and 8880 ppb.h for the NF+ treatments. For poplar ozone exposure caused highly significant reductions in growth rate, light-saturated net CO(2) assimilation rate, stomatal conductance, F(v)/F(m) and chlorophyll content. The largest effects were observed in August at which time ozone concentrations were elevated. A reduction was noticed in new leaf production, while accelerated ageing and visible damage to leaves caused high leaf losses. For beech the responses were similar but less pronounced: ozone exposure resulted in non-significant growth reductions, slight changes in light-saturated photosynthesis and accelerated leaf abscission. The chlorophyll content of beech leaves was not affected by the ozone treatments. The results confirmed previous observations that fast-growing tree species, such as most poplar species and hybrids, are more sensitive and responsive to tropospheric ozone than slower-growing species, such as beech. The growth reductions observed and reported here for beech were within the range of those reported in relationship to the AOT40 (accumulated exposure over a threshold of 40 ppb) critical level for ozone.     

Increasing interannual and altitudinal ozone mixing ratios in the Catalan Pyrenees

Interannual, seasonal, daily and altitudinal patterns of tropospheric ozone mixing ratios, as well as ozone phytotoxicity and the relationship with NO_x precursors and meteorological variables were monitored in the Central Catalan Pyrenees (Meranges valley and Forest of Guils) over a period of 5 years (2004–2008). Biweekly measurements using Radiello passive samplers were taken along two altitudinal transects comprised of thirteen stations ranging from 1040 to 2300 m a.s.l. Visual symptoms of ozone damage in Bel-W3 tobacco cultivars were evaluated biweekly for the first three years (2004–2006). High ozone mixing ratios, always above forest and vegetation protection AOT40 thresholds, were monitored every year. In the last 14 years, the AOT40 (Apr–Sept.) has increased significantly by 1047 μg m^?3 h per year. Annual means of ozone mixing ratios ranged between 38 and 67 ppb_v (38 and 74 ppb_v during the warm period) at the highest site (2300 m) and increased at a rate of 5.1 ppb_v year^?1. The ozone mixing ratios were also on average 35–38% greater during the warm period and had a characteristic daily pattern with minimum values in the early morning, a rise during the morning and a decline overnight, that was less marked the higher the altitude. Whereas ozone mixing ratios increased significantly with altitude from 35 ppb_v at 1040 m–56 ppb_v at 2300 m (on average for 2004–2007 period), NO₂ mixing ratios decreased with altitude from 5.5 ppb_v at 1040 m–1 ppb_v at 2300 m. The analysis of meteorological variables and NO_x values suggests that the ozone mainly originated from urban areas and was transported to high-mountain sites, remaining aloft in absence of NO. Ozone damage rates increased with altitude in response to increasing O₃ mixing ratios and a possible increase in O₃ uptake due to more favorable microclimatic conditions found at higher altitude, which confirms Bel-W3 as a suitable biomonitor for ozone concentrations during summer time. Compared to the valley-bottom site the annual means of ozone mixing ratios are 37% larger in the higher sites. Thus the AOT40 for the forest and vegetation protection threshold is greatly exceeded at higher sites. This could have substantial effects on plant life at high altitudes in the Pyrenees.     

Modelling critical levels of ozone for the forested area of austria modifications of the aot40 concept

GOAL, SCOPE AND BACKGROUND: Ozone is the most important air pollutant in Europe for forest ecosystems and the increase in the last decades is significant. The ozone impact on forests can be calculated and mapped based on the provisional European Critical Level (AOT40 = accumulated exposure over a threshold of 40 ppb, 10,000 ppb x h for 6 months of one growing season calculated for 24 h day(-1)). For Norway spruce, the Austrian main tree species, the ozone risk was assessed in a basis approach and because the calculations do not reflect the health status of forests in Austria, the AOT40 concept was developed. METHODS: Three approaches were outlined and maps were generated for Norway spruce forests covering the entire area of Austria. The 1st approach modifies the AOT40 due to the assumption that forests have adapted to the pre-industrial levels of ozone, which increase with altitude (AOTalt). The 2nd approach modifies the AOT40 according to the ozone concentration in the sub-stomata cavity. This approach is based on such factors as light intensity and water vapour saturation deficit, which affect stomatal uptake (AOTsto). The 3rd approach combines both approaches and includes the hemeroby. The pre-industrial ozone level approach was applied for autochthonous ('natural') forest areas, the ozone-uptake approach for non-autochthonous ('altered') forest areas. RESULTS AND DISCUSSION: The provisional Critical Level (AOT40) was established to allow a uniform assessment of the ozone risk for forested areas in Europe. In Austria, where ozone risk is assessed with utmost accuracy due to the dense grid of monitoring plots of the Forest Inventory and because the continuously collected data from more than 100 air quality measuring stations, an exceedance up to the five fold of the Critical Level was found. The result could lead to a yield loss of up to 30-40% and to a severe deterioration in the forest health status. However, the data of the Austrian Forest Inventory and the Austrian Forest Damage Monitoring System do not reflect such an ozone impact. Therefore, various approaches were outlined including the tolerance and avoidance mechanisms of Norway spruce against ozone impact. Taking into consideration the adaptation of forests to the pre-industrial background level of ozone, the AOT40 exceedances are markedly reduced (1st approach). Taking into account the stomatal uptake of ozone, unrealistic high amounts of exceedances up to 10,000 ppb x h were found. The modelled risk does not correspond with the health status and the wood increment of the Austrian forests (2nd approach). Consolidating the forgoing two approaches, a final map including the hemeroby was generated. It became clear that the less natural ('altered') forested regions are highly polluted. This means, that more than half of the spruce forests are endangered by ozone impact and AOT40 values of up to 30,000 ppb x h occur (3rd approach). CONCLUSIONS: The approaches revealed that a plausible result concerning the ozone impact on spruce forests in Austria could only be reached by combining pre-industrial ozone levels, ozone flux into the spruce needles and the hemeroby of forests.     

Origin of Bel-W3, Bel-C and Bel-B tobacco varieties and their use as indicators of ozone

Since 1962, the tobacco variety Bel-W3 (Nicotiana tabacum L.), has been used in many countries as an indicator of the presence of phytotoxic concentrations of O(3). It is super-sensitive to O(3) and may produce easily recognizable symptoms for several weeks on the new, fully expanded leaves. Bel-B and Bel-C, tolerant and sensitive to O(3), respectively, are sometimes used along with Bel-W3. Information is provided on the origin and nature of these varieties. This includes their use as indicators of elevated O(3) concentrations, strength and limitations, and the inheritance and nature of resistance to O(3) in Bel-B. The varieties were the product of research initiated in 1957 to determine the cause and to reduce losses from tobacco weather fleck. Bel-C and Bel-B display the classical upper leaf surface injury; whereas, Bel-W3 develops primarily bifacial lesions. Data are provided to show differences in the amounts of acute and chronic injury on each variety when exposed to different O(3) exposure doses in controlled environments and under field conditions. There is discussion of the influence of environmental factors on response to O(3) by the varieties and the possibility of synergistic action of O(3) and SO(3) when tobacco is exposed to mixtures of these gases. The methods and results obtained with Bel-W3 in the Dutch National Monitoring Network for Air Pollution are presented in detail. Use of Bel-W3 world-wide as an indicator of elevated O(3) concentrations has been a significant factor in increasing the awareness of O(3) as a pollutant.     

Preliminary assessment of risk of ozone impacts to maize (Zea mays) in southern Africa

Surface ozone concentrations in southern Africa exceed air quality guidelines set to protect agricultural crops. This paper addresses a knowledge gap by performing a preliminary assessment of potential ozone impacts on vegetation in southern African. Maize (Zea mays L.) is the receptor of interest in the main maize producing countries, i.e. South Africa, Zambia and Zimbabwe. Surface ozone concentrations are estimated for the growing season (October to April) using photochemical modelling. Hourly mean modelled ozone concentrations ranged between 19.7 and 31.2 ppb, while maximums range between 28.9 and 61.9 ppb, and are near 30 ppb over South Africa and Zambia, while in Zimbabwe, they exceed 40 ppb and translate into monthly AOT40 values of over 3,000 ppb h in five of the seven months of the growing season. This study suggests that surface ozone may pose a threat to agricultural production in southern African, particularly in Zimbabwe.     

Estimates of ozone AOT40 from passive sampling in forest sites in South-Western Europe

Weekly-fortnightly ozone (O3) concentrations measured by passive sampling at 81 forest monitoring plots in France, Italy, Spain and Switzerland over the period 2000-2002 were used to estimate the cumulative exposure index AOT40. The estimation method is based on a deterministic model which describes the O3 daily profile as a function of relative altitude (the difference between the altitude of the site and the lowest altitude within a 5 km radius) and the time of the day. Estimated AOT40 values (AOT40(e)) were evaluated against co-located automatic measurement stations and with 14 independent automatic stations located throughout Italy whose weekly mean O3 values were used to simulate passive samplers. AOT40 can be predicted by modelling passive sampling data (R2: 0.90; P<0.0001, SE of estimates: 3271 ppb h), although considerable deviations can occur for individual sites. Estimated AOT40 shows a distinct, significant latitudinal and altitudinal gradient. Taking the 3-year average as a whole, exceedance of critical level of 5000 ppb h occurs at 77-100% of the monitored sites, respectively.     

Ozone air pollution and foliar injury development on native plants of Switzerland

The objectives of this study were to examine the foliar sensitivity to ozone exposure of 12 tree, shrub, and herbaceous species native to southern Switzerland and determine the seasonal cumulative ozone exposures required to induce visible foliar injury. The study was conducted from the beginning of May through the end of August during 2000 and 2001 using an open-top chamber research facility located within the Lattecaldo Cantonal Forest Nursery in Canton Ticino, southern Switzerland (600 m asl). Plants were examined daily and dates of initial foliar injury were recorded in order to determine the cumulative AOT40 ppb h ozone exposure required to cause visible foliar injury. Plant responses to ozone varied significantly among species; 11 species exhibited visible symptoms typical of exposures to ambient ozone. The symptomatic species (from most to least sensitive) were Populus nigra, Viburnum lantana, Salix alba, Crataegus monogyna, Viburnum opulus, Tilia platyphyllos, Cornus alba, Prunus avium, Fraxinus excelsior, Ribes alpinum, and Tilia cordata; Clematis spp. did not show foliar symptoms. Of the 11 symptomatic species, five showed initial injury below the critical level AOT40 10 ppmh O3 in the 2001 season.     

Differences in growth, leaf senescence and injury, and stomatal density in birch (Betula pendula Roth.) in relation to ambient levels of ozone in Finland

The differences in growth, leaf senescence, visible ozone injuries and stomatal density between one coastal site (natural ozone) and two inland sites (natural and elevated ozone) in Finland were determined for saplings of Betula pendula clones grown under open-field conditions during two growing seasons. Responses in growth, leaf senescence, visible injuries, and stomatal density were determined in relation to cumulative ozone exposure accumulated over the thresholds of 30, 40 and 50 ppb (10(9)) during the exposure period. In addition, the effects of the different ozone exposures on ultrastructure of chloroplasts were studied. Increasing ozone exposure resulted in reduced shoot dry weight, stimulated (first year) or reduced (second year) height growth, accelerated autumn yellowing of leaves, increased stomatal density, visible symptoms and chloroplast injuries, and increased number and size of plastoglobuli. Newly expanded mature leaves in midsummer were more sensitive to ozone episodes than younger developing leaves in the early growing season. In most parameters, the best correlation was achieved with the exposure index AOT30. Ozone risk for birch is highest in the southern coastal area of Finland, where background ozone concentrations are higher than in inland sites.     

The use of light and electron microscopy to assess the impact of ozone on Norway spruce needles

Light (LM) and transmission electron (TEM) microscopy were used to study previously specified ozone symptoms in the foliage of Norway spruce. The three youngest green needle generations from twenty mature trees in two stands on sites of different soil fertility at Asa, southern Sweden, were sampled in 1999. The critical dose of ozone, expressed as AOT40, was 6,362 ppb.h. LM showed ozone-specific symptoms: decreased chloroplast size with electron dense stroma advancing gradually from the outer to the inner cell layers, being most severe in the needle side facing the sky. The symptoms were expressed as ozone syndrome indices at the needle generation, tree and stand levels. The index had higher values at the low fertility site. TEM was used to confirm the LM results. The study shows that LM can be used for diagnosis of the impact of ozone on conifers in the field.