Ozone-enriched Air Research Articles

Spatial and temporal variability of ozone along the Colorado Front Range occurring over 2 days with contrasting wind flow

Transport of pollution into pristine wilderness areas is of concern for both federal and state agencies. Assessing such transport in complex terrain is a challenge when relying solely on data from standard federal or state air quality monitoring networks because of the sparsity of network monitors beyond urban areas. During the Front Range air quality study, conducted in the summer of 2008 in the vicinity of Denver, CO, research-grade surface air quality data, vertical wind profiles and mixing heights obtained by radar wind profilers, and ozone profile data obtained by an airborne ozone differential absorption lidar augmented the local regulatory monitoring networks. Measurements from this study were taken on 2 successive days at the end of July 2008. On the first day, the prevailing winds were downslope westerly, advecting pollution to the east of the Front Range metropolitan areas. On this day, chemistry measurements at the mountain and foothills surface stations showed seasonal background ozone levels of approximately 55–68 ppbv (nmol mol–1 by volume). The next day, upslope winds prevailed, advecting pollution from the Plains into the Rocky Mountains and across the Continental Divide. Mountain stations measured ozone values greater than 90 ppbv, comparable to, or greater than, nearby urban measurements. The measurements show the progression of the ozone-enriched air into the mountains and tie the westward intrusion into high-elevation mountain sites to the growth of the afternoon boundary layer. Thus, under deep upslope flow conditions, ozone-enriched air can be advected into wilderness areas of the Rocky Mountains. Our findings highlight a process that is likely to be an important ozone transport mechanism in mountainous terrain adjacent to ozone source areas when the right circumstances come together, namely a deep layer of light winds toward a mountain barrier coincident with a deep regional boundary layer.

Enhanced recalcitrant pollutant degradation using hydroxyl radicals generated using ozone and bioelectricity-driven cathodic hydrogen peroxide production: Bio-E-Peroxone process

Accelerated pollutant degradation was examined using a new combined chemical and bioelectrochemical system, called a Bio-E-Peroxone process, based on generating ⋅OH from H2O2 produced on the cathode of a microbial fuel cell (MFC) and using ozone-enriched air. To optimize H2O2 formation, different carbon materials were examined and the highest H2O2 rates were obtained using XC-72 carbon black cathode. In E-Peroxone tests using the XC-72 cathode, methylene blue (a model pollutant) degradation rates followed first-order kinetics, with a rate constant of 0.237 min−1, 6 times higher than that obtained using only ozonation (0.032 min−1), 15 times of electrolysis+O2 system (0.015 min−1) and 46 times greater than electrolysis (0.005 min−1). In MFC tests when using the complete Bio-E-Peroxone system, the removal rate constant for methylene blue was 2.05 h−1, compared to 1.86 h−1 using only ozone and 0.41 h−1 using only MFC. Adding ozone to the air in cathode also increased power production by 47% to 170 mW m−3. The results demonstrated that this Bio-E-Peroxone system could be a feasible method for both refractory compounds degradation and wastewater electricity generation.

The Effects of Ozone-Enriched Storage Atmosphere on Pesticide Residues and Physicochemical Properties of Table Grapes

ABSTRACTThe persistence of residues of some common pesticides was investigated during the cold storage of table grapes in atmospheres of air or 0.64 mg m−3 ozone-enriched air. Residues of two of six pesticides evaluated in the study declined more rapidly in the ozone atmosphere than in air. The highest effect of ozone was on azoxystrobin fungicide. Decrease in the level of this pesticide was 2.8-fold higher in the samples stored in ozone atmosphere than that in air. Ozone did not cause any significant differences in Brix, pH, and total acidity values but increased the weight loss by about 1%.

Influence of the wintertime North Atlantic Oscillation on European tropospheric composition: an observational and modelling study

Abstract. We have used satellite observations and a simulation from the TOMCAT chemistry transport model (CTM) to investigate the influence of the well-known wintertime North Atlantic Oscillation (NAO) on European tropospheric composition. Under the positive phase of the NAO (NAO-high), strong westerlies tend to enhance transport of European pollution (e.g. nitrogen oxides, NOx; carbon monoxide, CO) away from anthropogenic source regions. In contrast, during the negative phase of the NAO (NAO-low), more stable meteorological conditions lead to a build-up of pollutants over these regions relative to the wintertime average pollution levels. However, the secondary pollutant ozone shows the opposite signal of larger values during NAO-high. NAO-high introduces Atlantic ozone-enriched air into Europe, while under NAO-low westerly transport of ozone is reduced, yielding lower values over Europe. Furthermore, ozone concentrations are also decreased by chemical loss through the reaction with accumulated primary pollutants such as nitric oxide (NO) in NAO-low. Peroxyacetyl nitrate (PAN) in the upper troposphere–lower stratosphere (UTLS) peaks over Iceland and southern Greenland in NAO-low, between 200 and 100 hPa, consistent with the trapping by an anticyclone at this altitude. Model simulations show that enhanced PAN over Iceland and southern Greenland in NAO-low is associated with vertical transport of polluted air from the mid-troposphere into the UTLS. Overall, this work shows that NAO circulation patterns are an important governing factor for European wintertime composition and air pollution.

Convective storms and non-classical low-level jets during high ozone level episodes in the Amazon region: An ARM/GOAMAZON case study

In this work, we investigate the ozone dynamics during the occurrence of both downdrafts associated with mesoscale convective storms and non-classical low-level jets. Extensive data sets, comprised of air chemistry and meteorological observations made in the Amazon region of Brazil over the course of 2014–15, are analyzed to address several questions. A first objective is to investigate the atmospheric thermodynamic and dynamic conditions associated with storm-generated ozone enhancements in the Amazon region. A second objective is to determine the magnitude and the frequency of ground-level ozone enhancements related to low-level jets. Ozone enhancements are analyzed as a function of wind shear, low-level jet maximum wind speed, and altitude of jet core. Strong and sudden increases in ozone levels are associated with simultaneous changes in variables such as horizontal wind speed, convective available potential energy, turbulence intensity and vertical velocity skewness. Rapid increases in vertical velocity skewness give support to the hypothesis that the ozone enhancements are directly related to downdrafts. Low-level jets associated with advancing density currents are often present during and after storm downdrafts that transport ozone-enriched air from aloft to the surface.

The ozone-like syndrome in durum wheat (Triticum durum Desf.): Mechanisms underlying the different symptomatic responses of two sensitive cultivars

Colombo and Sculptur are two modern durum wheat cultivars that, in previous studies, proved to be very sensitive to ozone injury in terms of eco-physiological parameters and significant grain yield loss. Nevertheless, their response regarding leaf visible symptoms was very different; Sculptur showed almost no symptoms, even after several weeks of ozone exposure, whereas Colombo showed in a few weeks typical ozone-like symptoms (chlorotic/necrotic spots). The mechanisms underlying this different response has been studied with a biochemical and microscopical approach. Plants were grown in Open-Top Chambers (OTCs) and exposed to charcoal filtered and ozone enriched air. Flag leaves were analyzed at two phenological stages (pre- and post-anthesis). At pre-anthesis the ascorbate pool was significantly lower in Colombo, which also underwent an increase in the oxidized glutathione content and abundant H2O2 deposition in mesophyll cells around the substomatal chamber. No or scarce H2O2 was found at both phenological stages in ozone exposed leaf tissues of Sculptur, where stomata appeared often closed. In this cultivar, transmission electron microscopy showed that chloroplasts in apparently undamaged mesophyll cells were slightly swollen and presented numerous plastoglobuli, as a result of a mild oxidative stress. These results suggest that Sculptur leaves remains symptomless as a consequence of the higher content of constitutive ascorbate pool and the synergistic effect of stomata closure. Instead, Colombo shows chlorotic/necrotic symptoms because of the lower ROS (Reactive Oxygen Species) scavenging capacity and the less efficient stomata closure that lead to severe damages of groups of the mesophyll cells, however leaving the surrounding photosynthetic tissue functional.

Contrasting effects of water salinity and ozone concentration on two cultivars of durum wheat (Triticum durum Desf.) in Mediterranean conditions

This paper reports the results of an Open-Top Chambers experiment on the responses of two durum wheat cultivars (Neodur and Virgilio) exposed to two different levels of ozone (charcoal-filtered air and ozone-enriched air) and irrigation water salinity (tap water as control and a 75 mM NaCl solution once a week).The stomatal conductance of the flag leaves was measured on four dates during May. Flag leaf samples were collected to detect ozone visible leaf injuries. At the end of the growing season, the yield/biomass and grain quality parameters were assessed. Saline irrigation caused significant reductions in gs, yield and grain quality in Neodur, while Virgilio was more tolerant. The yield response to ozone was almost negligible, with Virgilio, despite the higher susceptibility to visible leaf injuries, being more productive than Neodur.The responses to the combined stress were not consistent, with the main tendencies undoubtedly driven by the saline irrigation factor.

Reversible phytochrome regulation influenced the severity of ozone-induced visible foliar injuries in Trifolium subterraneum L.

In Trifolium subterraneum, oxidative stress caused by ozone has been shown to result in more severe visible foliar injuries when plants were kept in dim broadband white light during the night (i.e. a long photoperiod) compared to darkness during the night (a short photoperiod). As phytochrome signalling is involved in photoperiod sensing, the effect of night-time red and far-red illumination on the ozone-induced response was studied. T. subterraneum plants were treated with ozone enriched air (70 ppb) for either 1 h for a single day or 6 h for three consecutive days. After the first ozone exposure, plants were separated into six night-time light regimes during the two subsequent nights (10 h day, 14 h night): (1) darkness, (2) far-red light (FR), (3) a short night-break of red followed by far-red light during an otherwise dark night (R FR), (4) a short night-break of red, far-red and finally red light during an otherwise dark night (R FR R), (5) dim white light (L) and (6) red light (R). The treatments L and R resulted in significantly more severe ozone-induced visible foliar injuries relative to D and FR treatments, indicating a phytochrome-mediated response. The night-breaks resulted in a photoreversible and significantly different ozone response depending on the light quality of the last light interval (R FR or R FR R), supporting a photoreversible (between Pr and Pfr) phytochrome signalling response. Thus, in T. subterraneum, the outcome of oxidative stress due to ozone appears to depend on the photoperiod mediated by the night-time conformation of phytochrome.

Effect of continuous 0.3 μL/L gaseous ozone exposure on fungicide residues on table grape berries

The persistence of residues of some fungicides, commonly applied in table grape vineyards to reduce bunch rot, was investigated during the cold storage of ‘Thompson Seedless’ table grape stemmed berries in atmospheres of air or 0.3 μL/L ozone enriched air. Grape berries were sprayed with a mixture of boscalid, iprodione, fenhexamid, cyprodinil, and pyrimethanil solutions, dried in air for 24 h, and packed in plastic clamshell containers in expanded polystyrene boxes. The boxes were stored either in ozone or in ambient air atmosphere (2 °C, 95% RH) for 36 d. Residue analyses were done initially and at 12-d intervals using gas chromatography–mass spectrometry. Residues of boscalid, iprodione, fenhexamid, and pyrimethanil declined during storage in air, but cyprodinil residues did not change significantly during 36-d storage. Storage in the ozone atmosphere markedly accelerated the rates of decline of fenhexamid, cyprodinil, and pyrimethanil, but not those of boscalid or iprodione. At the end of storage, degradation of fenhexamid, cyprodinil, or pyrimethanil was 1.6-, 2.8-, or 3.6-fold higher, respectively, in the ozone atmosphere compared that in air. Despite their structural similarity, pyrimethanil declined more rapidly in an ozone atmosphere than cyprodinil. Fenhexamid declined in both air and ozone more rapidly than the other fungicides; at the end of storage period, only 59.2% or 35.5% of the initial residue remained after air or ozone storage, respectively. Our results have shown that gaseous ozone treatment during storage has a great potential for degrading contemporary fungicides related to table grape production.

Ozonation of Odorous Compounds in Gases Emitted from Rubber Processing Industries

This study aimed at the removal of odorous compounds in gases emitted from rubber processing industries. Simulated odorous gas for test was prepared by mixing fresh air and an odorous gas drawn from an oven in which a sample of rubber powder was kept either at 160°C (for a thermal plastic rubber) or 200°C (for a thermal setting rubber). The prepared odorous gas was then premixed with a definite amount of ozone-enriched air and introduced into a contact system. The contact system consists of two sieve-plate columns connected in series and each column has four 1-L chambers. Depending on with or without introducing circulating scrubbing water into the columns, the oxidation reaction could be either wet or dry one. Results indicate the wet oxidation got better performances than the dry one. The former got 97 and over 90% removal of VOCs (volatile organic compounds) and odorous intensity removal, respectively, with the operation conditions of initial ozone concentration 4.0 ppm, THC (total hydrocarbon) concentrations 6.5–10.3 ppm (methane equivalent), oxidation temperature 37.3°C, gas empty bed retention time (EBRT) 12 s, and liquid/gas rate ratio 0.01 m3/m3. With conditions similar to those cited above, odor concentration (dilutions to the threshold, D/T) in the test gas could be reduced from 1,738–3,090 to 31–98 with EBRTs of 11.4–14.5 s. Activated carbon is effective for both physical and chemical removals of residual VOCs, odorous compounds, and ozone in the effluent gas from the ozonation system. Economical analysis indicates that around US$ 0.16 is required for treating 1,000 m3 of the tested foul gas by the proposed ozonation process.

Effect of cold storage and ozone treatment on physicochemical parameters, soluble sugars and organic acids in Actinidia deliciosa

The production of kiwi fruits is a dynamic agricultural activity in Corsica (France). The fruits are either consumed directly or used to produce kiwi wine. They are often stored for 4–6 months in industrial freezer chambers at 0 °C or industrial ozone chambers. The aim of this study was to measure physical, chemical and fungicidal parameters, soluble sugars and non-volatile organic acids during storage in each of these types of chamber. Various standard and instrumental methods (physicochemical techniques, HPLC) in conjunction with statistical analysis were used. During storage, the kiwi mass, firmness and acidity decreased, whereas reducing sugar, °Brix and pH increased. There were statistical differences between the two chambers regarding reducing sugar and acidity. The ozone gas treatment had a fungicidal effect on Botrytis cinerea. The major soluble sugar present in the kiwi fruit was fructose, followed by glucose and sucrose. The concentrations of these sugars increased during storage in both air at 0 °C and ozone-enriched air. Organic acids are one of the important factors influencing fruit flavour. Citric and quinic acids predominated over malic, tartaric and ascorbic acids. During storage in the ozone chamber, concentrations of non-volatile organic acids decreased sharply after 25 weeks. Storage at 0 °C enabled better retention of organic acids.

Effect of cyclic exposure to ozone gas on physicochemical, sensorial and microbial quality of whole and sliced tomatoes

The effect of a humidified flow of ozone-enriched air applied cyclically (4 ± 0.5 μL L −1 of O 3 for 30 min every 3 h) on metabolic behaviour and sensorial and microbial quality of whole and fresh-cut ‘Thomas’ tomatoes stored up to 15 days at 5 °C was examined. The application of O 3 initially stimulated the respiration rate in a way similar to a stress, although after 2 days, the metabolic activity decreased to a rate lower than that of control (air flow). In O 3-treated whole and sliced tomatoes a higher sugar (fructose and glucose) and organic acid (ascorbic and fumaric) content was found. The kind of cut (whole or slices) did not affect the sensitivity of tomato to O 3. In whole tomatoes, O 3 maintained the tissue firmer than in control fruit while no influence was found on slices. The O 3 treated fruit retained a good appearance and overall quality in slices but experienced a reduced aroma. Also, O 3 substantially reduced microbial counts, being more noticeable on bacteria (1.1–1.2 log 10 units) than on fungi (0.5 log 10 units). This effect was higher when the storage time was longer and when a higher O 3 level (7 μL L −1) was used. O 3 did not cause any damage or off-flavour in slices or whole tomatoes. In conclusion, the assayed O 3 treatment can be useful for maintaining quality and reducing microbial populations in whole and sliced tomato.

Mechanisms underlying the amelioration of O3-induced damage by elevated atmospheric concentrations of CO2.

There is growing evidence that rising atmospheric CO2 concentrations will reduce or prevent reductions in the growth and productivity of C3 crops attributable to ozone (O3) pollution. In this study, the role of pollutant exclusion in mediating this response was investigated through growth chamber-based investigations on leaves 4 and 7 of spring wheat (Triticum aestivum cv. Hanno). In the core experiments, plants were raised at two atmospheric CO2 concentrations (ambient [350 micro l l(-1)] or elevated CO2 [700 micro l l(-1)] under two O3 regimes (charcoal/Purafil-filtered air [<5 nl l(-1) O3] or ozone-enriched air [75 nl l(-1) 7 h d(-1)]). A subsequent experiment used an additional O3 treatment where the goal was to achieve equivalent daily O3 uptake over the life-span of leaves 4 and 7 under ambient and CO2-enriched conditions, through daily adjustment of exposures based on measured shifts in stomatal conductance. Plant growth and net CO2 assimilation were stimulated by CO2-enrichment and reduced by exposure to O3. However, the impacts of O3 decreased with plant age (i.e. leaf 7 was more resistant to O3 injury than leaf 4); a finding consistent with ontogenic shifts in the tolerance of plant tissue and/or acclimation to O3-induced oxidative stress. In the combined treatment, elevated CO2 protected against the adverse effects of O3 and reduced cumulative O3 uptake (calculated from measurements of stomatal conductance) by c. 10% and 35% over the life-span of leaves 4 and 7, respectively. Analysis of the relationship between O3 uptake and the decline in the maximum in vivo rate of Rubisco carboxylation (Vcmax) revealed the protection afforded by CO2-enrichment to be due, to a large extent, to the exclusion of the pollutant from the leaf interior (as a consequence of the decline in stomatal conductance triggered by CO2-enrichment), but there was evidence (especially from flux-response relationships constructed for leaf 4) that CO2-enrichment resulted in additional effects that alleviated the impacts of ozone-induced oxidative stress on photosynthesis.

Design and performance of a free-air exposure system to study long-term effects of ozone on grasslands

Studying long-term effects of ozone on perennial plant communities in situ is difficult because of the need for large observation plots and long exposure times, and because of confounding effects of altered microclimatic conditions in most systems. A novel free-air fumigation system was designed for multi-year exposures of semi-natural grassland plots to either ambient or elevated ozone concentrations at a Swiss sub-alpine site. The system operates by releasing ozone-enriched air from either one of two 120° sectors, placed in each of the two main wind directions. Ozone-enriched air is rapidly mixed with ambient air behind a small transparent windscreen mounted at canopy height around the 7-m diameter circular plots. Ozone generation and dispensing during daylight hours is PC controlled and depends upon wind speed, wind direction and ambient ozone. In 2001, from April to October fumigation was possible during 85% of the time. The ozone-enrichment factor (EF, [O 3] enriched/[O 3] control) in ozone plots relative to control plots averaged 1.48 (±0.24 SD), and EF was highest with winds of around 2 m s −1. The seasonal cumulative ozone exposure (AOT40) at canopy level was 5 ppm h in the control and 30 ppm h in the ozone-treated plots, with less than 10% variation between replicates, and 13 ppm h in ambient air at 2 m. Variation in ozone across the plot-diameter was <5% for 24-h mean concentrations, but differed by a maximum of 20% in terms of AOT40. There was no difference in microclimatic conditions between experimental plots and ambient conditions. It is concluded that the system is suitable for long-term ozone experiments at relatively low running costs, but that the variation in ozone distribution across the plots may lead to systematic differences in cumulative exposure over longer periods of time which need to be taken into account when relating exposure to biological effects.

Image analysis of the stomatal cell walls of Picea abies (L.) Karst. in pure and ozone-enriched air

The method of image analysis was used to re-investigate previously described structural changes in spruce needles following their exposure to ozone. The changes observed in fumigation experiments were compared with the modifications observed at a site with a similar ozone load. Use was made in each case of needles for which the varying behavioural patterns were known from physiological experiments. In samples with reduced ability to regulate stomatal aperture, the cell walls of the stomatal apparatus showed a reduction in absorptive power at 280 nm. This was interpreted to be a result of delignification of the cell walls in question due to the direct impact of ozone on the surface of the needle.

Experiments on the water balance of individual attached twigs of Picea abies (L .) Karst. in pure and ozone-enriched air

Rates of transpiration and xylem sap flow were continuously measured in individual twigs in the upper crown of an 18-year-old spruce. Two gas exchange chambers were run simultaneously under identical conditions. One of two equivalent twigs was exposed to pure air whereas the other received the ozone-enriched air of the site. A third gas exchange chamber in mid-crown ran independently with normal outside air and was used for basic experiments. At certain times needles were sampled for water potential measurements. Chamber humidity was reduced step by step and the transpiration and xylem sap flow rates were permanently compared. It turned out that sap flow keeps up with transpiration without lagging as long as chamber humidity is high and the twigs outside the chamber are not subject to substantial evaporative demand. However, in warm summer weather and with high flow rates sap flow is no longer sufficient. As the balance quotient (uptake/release) of 0.8 was reached the stomata began to close and water balance improved. The flux quotient increased far above 1.0 without water potential of the needles, which had decreased before, increasing significantly. The balance quotient of the twig in ozone-enriched air fell to relatively low values and only increased again correspondingly slowly due to lagging stomatal closure. Despite increased water uptake after the light phase, the ozone-treated twig ran into a water deficit in the daily balance during the course of an uninterrupted drought period. Water deficit increased from day to day and only disappeared with the next rainfall. For providing insight into the ozone effect shown in this study it was thought necessary to discuss comprehensively the controversial views of the stomatal control mechanism. The results show that the stomata react to small scale changes in water status as expected for an effective negative feedback system. The less sensitive reaction of the stomata under the influence of ozone confirms earlier results. Increased severity and duration of the daily drought stress loads were attributed to a lag in adjustment due to poor stomatal control. The demonstrated function mechanism shows that the detrimental effect of ozone is dependent on weather conditions.

Variability of Near-Ground Ozone Concentrations During Cold Front Passages - a Possible Effect of Tropopause Folding Events

The analysis of surface ozone variability requires besides chemicalstudies the consideration of meteorological conditions and dynamicprocesses. Our research focuses on the mechanisms in connection with coldfront passages. A statistical study and case studies of cold front passageswere carried out at six German ground-based sites during the year 1990.After the passage of cold fronts three typical developments of thenear-ground ozone concentrations could be identified. Usually the ozoneconcentrations decrease due to advection of clean air masses or due toenhanced cloudiness preventing the photochemical production of ozone,chemical destruction by nitrogenoxides, and heterogeneous chemistry. In somecases the concentrations increased by reason of downward mixing of ozoneenriched air intruded from the stratosphere into the troposphere bytropopause foldings. For a few cases no modification set in. The decreasewas mostly twice as strong as the increase. The latter was between 4 and 8ppb on the average. Special emphasis is given to the transport ofstratospheric ozone down to the ground. There is no direct evidence forstratospheric ozone at ground level, because it can‘t be distinguished fromthe tropospheric one, but from case studies circumstantial evidence is foundin favour of it. As an example of increasing ozone behind the passage ofcold fronts one case study typical of all other case studies is presented.It shows the characteristic properties of the corresponding fronts, whichare fast movement, a vertical split structure and strong convection.

Photosynthetic and stomatal conductance responses of Norway spruce and beech to ozone, acid mist and frost—a conceptual model

Two-year-old beech and Norway spruce seedlings were exposed to a combination of ozone and acid mist treatments in open-top chambers in Scotland during the months of July through to September 1988. Replicate pairs of chambers received charcoal-filtered air (control), ozone-enriched air (140 nl ozone litre −1) or 140 nl ozone litre −1 plus a synthetic acid mist (pH 2·5) composed of ammonium nitrate and sulphuric acid. Field measurements of assimilation and stomatal conductance were made during August. In addition, measurements of assimilation and conductance were made during September in the laboratory. Light response curves of assimilation and conductance were determined using a GENSTAT nonrectangular hyperbolic model. During February 1988/9 the Norway spruce were subject to a four day warming period at 12°C and the light response of assimilation determined. The same plants were then subject to a 3-h night-time frost of −10°C. The following day the time-course of the recovery of assimilation was determined. It was found that ozone fumigation did not influence the light response of assimilation of beech trees in the field, although stomatal conductance was reduced in the ozone-fumigated trees. The rate of light-saturated assimilation of Norway spruce was increased by ozone fumigation when measured in the field. Measurements of assimilation of Norway spruce made during the winter showed that prior to rewarming there was no difference in the rate of light-saturated assimilation for control and ozone-fumigated trees. However, the ozone plus acid mist-treated trees exhibited a significantly higher rate. The 4-day period of warming to 12°C increased the rate of light-saturated assimilation in all treatments but only the ozone plus acid mist-treated trees showed a significant increase. Following a 3-h frost to −10°C the control trees exhibited a reduction in the rate of light-saturated assimilation (A max ) to 80% of the pre-frost value. In comparison, following the frost, the ozone-fumigated trees showed an A max of 74% of the pre-frost value. The ozone plus acid mist-treated trees showed an A max of 64% of the pre-frost trees. The time taken for A max to attain 50% of the pre-frost value increased from 30 min (control) to 85 min for ozone-fumigated trees to 190 min (ozone plus acid mist). These results are discussed in relation to the impact of mild, short-term frosts, which are known to occur with greater frequency than extreme, more catastrophic frost events. A simple conceptual framework is proposed to explain the variable results obtained in the literature with respect to the impact of ozone upon tree physiology.

The Effect of Ozone in Ambient Air on Ribulosebisphosphate Carboxylase/Oxygenase Activity Decreases Photosynthesis and Grain Yield in Wheat

Summary Wheat was grown in open-top chambers in the field and fumigated with charcoal-filtered air (0.02 µll -1 O 3 ), unfiltered air (0.035 µ ll -1 O 3 ) and air enriched with ozone (0.1 µll -1 O 3 [seasonal mean ozone concentration during 8 h per day, from 9 am to 5 pm]). Ambient plots were used for comparison. Dry matter production, grain yield, and the following photosynthetic parameters of flag leaves were determined: 14 CO 2 uptake in situ , CO 2 response of net photosynthesis in the laboratory, CO 2 compensation concentration, activity of ribulose hisphosphate carboxylase/oxygenase (RuBPCO) as initial activity after rapid extraction and as activity after incubation of the extract in the presence of CO 2 and Mg ++ , content of soluble protein and of chlorophyll, and stomatal resistance. Photosynthesis ( 14 CO 2 -fixation) of flag leaves at the beginning of anthesis and grain yield were highest in filtered air. In unfiltered air and in air enriched with ozone, photosynthesis was lower by 10% and 52%, respectively, and grain yield was lower by 12% and 57%, respectively. Net photosynthesis showed a proportional decrease at limiting and saturating C02 partial pressures. The decrease in net photosynthesis was associated with a decrease in the content of activatable RuBPCO and with an increase in the CO 2 compensation concentration. The degree of activation of RuBPCO in vivo increased with increasing ozone concentration. The content of soluble protein and of chlorophyll were similar in filtered and unfiltered air, slightly decreased in the open field plots and greatly decreased in ozone-enriched air. Stomatal resistance was only increased in ozone-enriched air. The results suggested that the response of photosynthesis to elevated ozone was the result of a limitation in the amount of RuBPCO present in the leaves and not of changes in CO 2 conductance or RuBP synthesis. Photosynthetic characteristics of leaves exposed to elevated ozone were similar to those found in senescing leaves. It is suggested that ozone induces premature senescence.

Ozone measurement survey in commercial jet aircraft.

Abstract : A survey was made to (1) measure ozone concentrations in CAR 4b jet aircraft cabins and cockpits on flights above 25,000 ft to obtain a 12-month evaluation with emphasis on seasonal and meteorological correlation and (2) locate and chart ozone-enriched air masses to obtain further correlations and to find any abnormal conditions that result in high ozone concentration. The data obtained by monitoring jets showed: (1) External ozone enters via the pressurization system. (2) Ozone concentration varies with altitude, latitude, and season. (3) Pressurization systems of various aircraft do not differ in ozone-decomposing efficiency. (4) Internal ozone concentration is negligible on flights made below the tropopause.