Catalytic oxidation of gaseous PCDD/Fs with ozone over iron oxide catalysts

Catalytic oxidation of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) with ozone (catalytic ozonation) over nano-sized iron oxides (denoted as FexOy) was carried out at temperature of 120-180 degrees C. The effects of operating temperature, ozone concentration, space velocity (SV) and water vapor contents on PCDD/F removal and destruction efficiencies via catalytic ozonation were investigated. High activity of the iron oxide catalyst towards PCDD/F decomposition was observed even at low temperatures with the aid of ozone. The PCDD/F removal and destruction efficiencies achieved with FexOy/O3 at 180 degrees C reach 94% and 91%, respectively. In the absence of ozone, the destruction efficiencies of all PCDD/F congeners are below 20% and decrease with increasing chlorination level of PCDD/F congener at lower temperature (120 degrees C). However, in the presence of ozone, the destruction efficiencies of all PCDD/F congeners are over 80% on FexOy/O3 at 180 degrees C. Higher temperature and ozone addition increase the activity of iron oxide for the decomposition of PCDD/Fs. Additionally, in the presence of 5% water vapor, the destruction efficiency of the PCDD/Fs is above 90% even at lower operating temperature (150 degrees C). It indicates that the presence of appropriate amount of water vapor enhances the catalytic activity for the decomposition of gas-phase PCDD/Fs.     

Ozone-driven photocatalyzed degradation and mineralization of pesticide,Triclopyr by Au/TiO2

Triclopyr is a widely used pesticide which is non-biodegradable and enters aquatic systems. The ozone facilitated photocatalyzed degradation and mineralization of Triclopyr using Au-loaded titania as heterogeneous catalyst is reported. The oxidative degradation activity of the hazardous pesticide was investigated at pH 7.8 under varied reaction conditions, including in presence and absence of ozone, titania alone, in presence and absence of light and with different loadings of Au on support. Photocatalysis with 2% Au/TiO₂ in the presence of ozone yielded 100% degradation of Triclopyr in 2 h. The extent of degradation of pesticide and its mineralization were confirmed by GC-MS. For 10 mg/L of Triclopyr, 0.1 g/L of catalyst was found to be the optimum for mineralization. Results show that photocatalyzed ozonation with Au/TiO₂ as catalyst is a very effective for its removal. No leaching of Au was observed in triplicate runs. Catalyst was fully recoverable and reusable with no loss of activity.     

Spatial mapping of VOC and NOx-limitation of ozone formation in central California

Ambient aerometric data were used to predict whether ozone formation at specific times and locations in central California was limited by the availability of volatile organic compounds (VOC) or oxides of nitrogen (NO_x). The predictions were compared with differences between mean weekday and weekend peak ozone values. The comparison with weekend and weekday ozone levels provided a means for empirically investigating the effects of VOC and NO_x reductions on ozone formation, because the relative proportions and levels of ozone precursor species were significantly different on weekends than on weekdays. Weekend NO_x levels averaged 27 percent lower than weekday levels at the time of the peak ozone hour. Daytime weekend levels of VOC species were also consistently lower than weekday values throughout the region, though the differences between weekends and weekdays were not always statistically significant (p<0.05). Site-to-site differences between weekend and weekday mean peak hourly ozone were related to whether ozone formation was VOC- or NO_x-limited.     

The role of nitrogen oxides in nonurban ozone formation in the planetary boundary layer over n America,w europe and adjacent areas of ocean

The status of knowledge on photochemical ozone formation and the effects of nitrogen oxides and peroxyacyl nitrates on such formation have been evaluated. The literature is reviewed on

• 1.(a) nonurban ozone and nitrogen oxide concentration distributions,(b) ozone lifetimes,(c) nitrogen oxide lifetimes, and(d) ozone formation in plumes as related to nitrogen oxide.

The modeling approaches applied to ozone formation

• 1.(a) with urban plumes,
• 2.(b) power plant plumes,
• 3.(c) high pressure systems, and
• 4.(d) during longerrange transport of ozone are discussed. In addition, models concerned with the contributions to ozone formation associated with reactions of natural hydrocarbons and nitrogen oxide near ground level and photochemical ozone formation associated with reactions of carbon monoxide and of more persistent organic species with nitrogen oxides in the free troposphere are considered.

It is concluded that urban plumes are major contributors to elevated ozone concentrations measured at nonurban locations, particularly during the passage of high pressure systems. Ozone can survive at significant concentration levels for more than one day of transport. However, the evidence for multiday ozone transport is to a large extent associated with transport over water.Ozone formation during the first day of transport does not appear to be limited by the availability of nitrogen oxides. However, it is likely that multiday formation and transport of ozone within the boundary layer is limited in duration because of the relatively short lifetimes of nitrogen oxides and peroxyacyl nitrates. Photochemical formation of ozone in the free troposphere may be an important contributor to longer-time average ozone concentrations in rural areas. These free tropospheric processes depend in part on anthropogenic sources of precursors and are especially sensitive to the vertical distribution of nitrogen oxides in the atmosphere.     

Summer ozone episodes in the Greater Madrid area. Analyzing the ozone response to abatement strategies by modelling

The development of ozone control strategies requires analysing the sensitivity of the dispersion model used to changes in emissions of nitrogen oxides (NO_X) and volatile organic compounds. The ozone response to variations in road traffic and total anthropogenic emissions is evaluated for two different summer ozone episodes in the Greater Madrid Area (GMA). This study uses the TVM model and a transport/chemistry module in which different chemical mechanisms (EMEP, RACM) are implemented. The results show that the areas of maximum impact and ozone responses are notably influenced by the different transport and dispersion patterns established in the area. However, the contribution of anthropogenic sources other than road traffic is patent in both episodes. Strategies based only on decreasing road traffic emissions were not sufficient for an effective control of the air quality in the GMA. Moreover, certain discrepancies observed in the predicted trends, as a response to these control strategies posed, reflect the importance of variations in the precursors balance. The ozone production regime associated to these ozone episodes and the sensitivity of the ozone response to changes in this balance has been investigated. A chemical indicator has been used to deepen in that evaluation.     

Hydrocarbon Production and Photochemical Ozone Formation in Forest Burn Plumes

The purpose of this paper is to describe ozone production in forest slash burn plumes. Plumes from controlled fires in the state of Washington were monitored using an instrumented aircraft. Ozone, oxides of nitrogen, condensation nuclei, and visual range (nephelometer) were measured continuously on board the plane. Airborne grab samples were collected for detailed hydrocarbon analysis.

The slash burn plumes were found to contain significant quantities of ozone. A buildup of 40–50 ppb above the ambient background ozone concentrations was not unusual. Hydrocarbon analyses revealed the presence of many photochemically reactive olefins in the plume. Hydrocarbon/NO _x ratios were favorable for photochemical oxidant production.     

Reactions of cloned poplars to air pollution

Ozone-induced changes in ethylene production, ACC oxidase activity and the contents of ACC, MACC and free PAs were studied inPopulus nigra L. cv. Loenen with high ozone sensitivity as judged by the degree of chlorophyll degradation and premature leaf abscission. Ethylene production, ACC oxidase activity, ACC content and MACC levels were induced by the one-, two-, and three-week ozone exposure (36±9 ppb O₃ for 11 hours a day). In addition, increases in PA levels, especially in spermidine, were measured in ozone treated plants. The role of free PAs and MACC synthesis as possible antisenescence reactions is discussed.     

Heterogeneous photochemical reactions of a propylene-nitrogen dioxide-metal oxide-dry air system

Photochemical reactions of a C₃H₆-NO₂-air system in the presence of metal oxide were investigated. The metal oxides showing strong photooxidation activity were found to be n-type semiconductor oxides with the energy band gap around 3 eV. Formation of cyano-compounds (HCN and CH₃CN) was also observed and the activity can be explained in terms of the adsorptivity of NO onto metal oxides. Coalfired fly ash as a model of mixed metal oxides was also examined and their photocatalytic action was discussed.     

Responses of spring wheat (Triticum aestivum L.) to ozone produced by either electric discharge and dry air or by UV-lamps and ambient air

The aim of the present study was to examine if ozone produced similar effects on spring wheat growth with and without small amounts of nitrogen oxides. Two methods were used to produce ozone: the first method consisted of dry pressurized air fed to an electric discharge generator generating the byproducts, N2O5 and N2O, the second method consisted of ambient air fed to UV-lamps. Two spring wheat cultivars (Triticum aestivum L. cvs Minaret and Eridano) were exposed in small open-top chambers to charcoal-filtered air, non-filtered ambient air, and non-filtered ambient air with the addition of ozone for 8 h (0900 to 1700 h) daily, for five weeks. Plants were harvested every week. The growth of Minaret was shown to be more sensitive to O3 than that of Eridano. Leaf senescence increased with increasing ozone level in both cultivars. The total above-ground biomass dry weight decreased with increasing ozone concentration in Minaret, but not in Eridano. The Minaret plants reacted with more damaged leaf dry weight and inhibition of growth when O3 was produced by UV-lamps than when O3 was produced by air fed to an electric discharge generator. This could be explained by more nitrogen content per plant but not by increased nitrogen concentration in plant tissue in plants exposed to increased O3 and small amounts of incidental nitrogen oxides.     

Selective Reduction of Nitrogen Oxides In Combustion Flue Gases

The body of Information presented in this paper is directed to those Individuals concerned with the removal of NO_x in combustion flue gases. A catalytic process for the selective reduction of nitrogen oxides by ammonia has been investigated. Efforts were made toward the development of catalysts resistant to SO_x poisoning. Nitrogen oxides were reduced over various metal oxide catalysts in the presence or absence of SO_x(SO₂ and SO₃). Catalysts consisting of oxides of base metals (for example, Fe₂O₃) were easily poisoned by SO₃, forming sulfates of the base metals. A series of catalysts which are not susceptible to the SO_x poisoning has been developed. The catalysts possess a high activity and selectivity over a wide range of temperatures, 250—450°C. The catalysts were tested in a pilot plant which treated a flue gas containing 110-150 ppm NO_x, 660-750 ppm SO₂, and 40-90 ppm SO₃. The pilot plant was operated at 350°C and at a space velocity of 10,000 h^-1. The removal of nitrogen oxides was more than 90% for several months.

A mechanism of the NO-NH₃ reaction has also been investigated. It is found that NO reacts with NH₃ at a 1:1 mole ratio in the presence of oxygen and the reaction is completely inhibited by the absence of oxygen. The experimental data show that the NO-NH₃ reaction in the presence of oxygen is represented byNO + NH₃ + 1/4 O₂ = N₂ + 3/2 H₂O.     

Measurements and analyses of nitrogen oxides and ozone in the yard and on the roof of a street-canyon in Suzhou

The concentrations of air pollutants such as nitrogen oxides and ozone characterised by very fast chemical reactions can significantly vary within urban street-canyon due to the short distances between sources and receptor. With the primary objective to analyse this issue, NO, NO₂, NO_x, O₃, BTX, and wind flow field were continuously measured for 1 week at two heights (a street-level yard and a 25-m-high rooftop) in an urban canyon in Suzhou (China). The yard ozone concentrations were found to be up to six times lower than on the roof. Different frequency distributions (FD), dynamical and chemical processes of the pollutant variations from yard to roof are discussed to explain the findings. The predominant factors for the dissimilar pollutant vertical diffusion at the two measurement locations were associated to dissimilar fluid-dynamic and heterogeneous removal effects that likely induced dissimilar ozone chemical processes relative to NO_x and BTX precursors.     

Cell size dependence of additive versus synergetic effects of UV radiation and PAHs on oceanic phytoplankton

Polycyclic Aromatic Hydrocarbons’ (PAHs) toxicity is enhanced by the presence of ultraviolet radiation (UVR), which levels have arisen due to the thinning of the ozone layer. In this study, PAHs’ phototoxicity for natural marine phytoplankton was tested. Different concentrations of a mixture of 16 PAHs were added to natural phytoplankton communities from the Mediterranean Sea, Atlantic, Arctic and Southern Oceans and exposed to natural sunlight received in situ, including treatments where the UVR bands were removed. PAHs’ toxicity was observed for all the phytoplankton groups studied in all the waters and treatments tested, but only for the pico-sized group a synergetic effect of the mixture and UVR was observed (p = 0.009). When comparing phototoxicity in phytoplankton from oligotrophic and eutrophic waters, synergy was only observed at the oligotrophic communities (p = 0.02) where pico-sized phytoplankton dominated. The degree of sensitivity was related to the trophic degree, decreasing as Chlorophyll a concentration increased.     

Ozone fumigation (twice ambient) reduces leaf infestation following natural and artificial inoculation by the endophytic fungus Apiognomonia errabunda of adult European beech trees

In 2006, a controlled infection study was performed in the ‘Kranzberger Forst’ to address the following questions: (1) Will massive artificial inoculation with Apiognomonia errabunda override the previously observed inhibitory effect of chronic ozone? (2) Can biochemical or molecular markers be detected to account for the action of ozone? To this end six adult beech trees were chosen, three ozone fumigated (2× ozone) and three control trees (ambient = 1× ozone). Spore-sprayed branches of sun and shade crown positions of each of the trees, and uninoculated control branches, were enclosed in 100-L plastic bags for one night to facilitate infection initiation. Samples were taken within a five-week period after inoculation. A. errabunda infestation levels quantified by real-time PCR increased in leaves that were not fumigated with additional ozone. Cell wall components and ACC (ethylene precursor 1-amino cyclopropane-1-carboxylic acid) increased upon ozone fumigation and may in part lead to the repression of fungal infection.     

Ozone uptake by citrus trees exposed to a range of ozone concentrations

The Citrus genus includes a large number of species and varieties widely cultivated in the Central Valley of California and in many other countries having similar Mediterranean climates. In the summer, orchards in California experience high levels of tropospheric ozone, formed by reactions of volatile organic compounds (VOC) with oxides of nitrogen (NO_x). Citrus trees may improve air quality in the orchard environment by taking up ozone through stomatal and non-stomatal mechanisms, but they may ultimately be detrimental to regional air quality by emitting biogenic VOC (BVOC) that oxidize to form ozone and secondary organic aerosol downwind of the site of emission. BVOC also play a key role in removing ozone through gas-phase chemical reactions in the intercellular spaces of the leaves and in ambient air outside the plants. Ozone is known to oxidize leaf tissues after entering stomata, resulting in decreased carbon assimilation and crop yield. To characterize ozone deposition and BVOC emissions for lemon (Citrus limon), mandarin (Citrus reticulata), and orange (Citrus sinensis), we designed branch enclosures that allowed direct measurement of fluxes under different physiological conditions in a controlled greenhouse environment. Average ozone uptake was up to 11 nmol s^?1 m^?2 of leaf. At low concentrations of ozone (40 ppb), measured ozone deposition was higher than expected ozone deposition modeled on the basis of stomatal aperture and ozone concentration. Our results were in better agreement with modeled values when we included non-stomatal ozone loss by reaction with gas-phase BVOC emitted from the citrus plants. At high ozone concentrations (160 ppb), the measured ozone deposition was lower than modeled, and we speculate that this indicates ozone accumulation in the leaf mesophyll.     

An examination of oxidant amounts on secondary organic aerosol formation and aging

The effect of HO_x radicals (OH and HO₂) and ozone (O₃) on aerosol formation and aging has been studied. Experiments were performed in presence as well as in absence of oxygen in a flow-through chamber at 299 K for three organic precursor gases, isoprene, α-pinene and m-xylene. The HO_x source was the UV photolysis of humidified air or nitrogen and was measured with a GTHOS (Ground-based Tropospheric Hydrogen Oxides Sensor). The precursor gases concentration was monitored with an online GC-FID. The aerosol mass was then quantified by a Tapered Element Oscillating Microbalance (TEOM). Typical oxidant mixing ratios were (0–4.5) ppm for O₃, 200 pptv for OH and 3 ppbv for HO₂. A simple kinetics model is used to infer the aerosol production mechanism. In the present of O₃ (or O₂), the SOA yields were 0.46, 0.036 and 0.12 for α-pinene with an initial concentration of 100 ppbv (RH = 37%), isoprene with an initial concentration of 177 ppbv (RH = 50%) and m-xylene with an initial concentration of 100 ppbv (RH = 37%), respectively. When the chosen precursor gases reacted with HO_x in the absence of O₃, the maximum SOA yields were significantly increased by factors of 1.6 for isoprene 1.1 for α-pinene, and 3 for m-xylene respectively. The comparison of the calculated and measured potential aerosol mass concentrations as function of time shows that presence of ozone or oxygen can influence the aerosol yield and the absence of ozone or oxygen in the system resulted in high concentrations of its organic aerosol products.     

Seasonal evolutions of ozone (O3) and its nitrogen precursors (NO, NO2) in urban Sfax (Tunisia)

Seasonal evolution of ozone (O3) and its nitrogen precursors (NO, NO2) in downtown Sfax (Tunisia) was monitored. Nitrogen oxides are shown to be closely related to local vehicle sources. Seasonal ozone levels, however, are shown to be dependent on regional meteorological conditions. High ozone levels are due to the effect of anticyclones and stratosphere intrusions (cut-off lows). Low levels are associated with cyclonic conditions of small vertical range of motion. Other than these particular conditions, ozone levels are shown to be relatively higher in fall and winter seasons, characterised by a very steady atmosphere. Overall, the examined meteorological conditions, the ozone concentrations observed in downtown Sfax are characterised by clear day/night cycles, which can be explained by the significant ventilation of the region.     

The use of ambient data to corroborate analyses of ozone control strategies

Data from environmental-chamber studies and photochemical box-model simulations were used to evaluate and revise a method for developing a qualitative understanding of the sensitivity of ozone formation at a particular time and place to changes in concentrations of volatile organic compounds (VOC) and oxides of nitrogen (NO_x). The revised method requires measurements of ozone, NO, and either NO_x or NO_y. The sensitivities of the method to biases in measurements were evaluated. The method potentially can be used for qualitative assessment of VOC versus NO_x limitation, comparison with the predictions of grid-based photochemical air-quality models, and evaluation of trends over time in the relative effectiveness of VOC versus NO_x controls.     

The relationship between EDU pre-treatment and C2H4 evolution in ozonated pea plants

A soil drench of [Formula: see text] (EDU) (150 ppm) applied to 'Progress No. 9' pea plants 24 h before an acute ozone exposure (0.25 ppm, 4 h) completely protected the foliage from visible symptoms normally induced by the pollutant. In the absence of ozone, EDU-treated plants were found to emit the same amount of C(2)H(4) as plants not treated with EDU. Based on this evidence, EDU-induced tolerance to ozone could not have been attributed to the prevention of an interaction between ethylene and ozone (sensu Mehlhorn and Wellburn). In the presence of ozone, EDU-treated plants did not emit the burst of C(2)H(4) that normally occurs (sensu Craker), extending the observation that EDU-treated plants do not exhibit the adverse physiological responses normally caused by ozone. The classic C(2)H(4) biosynthesis inhibitor aminoethoxyvinylglycine (AVG) did not prevent ozone phytotoxicity, although it significantly reduced ethylene emission from the ozonated tissue.     

Traffic pollution in a downtown site of Buenos Aires City

It has recently been recognized that air and noise pollution constitutes an extended problem over the densely populated city of Buenos Aires. Traffic emissions are of paramount concern, especially along narrow and main traffic arteries. In spite of these considerations, few systematic studies have been undertaken to evaluate the air quality in the metropolitan area of the city. In 1996, concentrations of carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO₂) and ozone (O₃) were simultaneously measured for the first time using a continuous monitoring station. This station was placed in a building at Belgrano Avenue, which is a heavy traffic street in the downtown area of the city (Bogo et al., Atmospheric Environment 33 (1999) 2587. In this work, we analyze the dependence of the measured primary pollutants, CO and the mixture of nitrogen oxides (NO_x), with meteorological conditions, traffic emissions and monitoring location. We compare the registered values with the results obtained from modeling the dispersion of the pollutants emitted from mobile and area sources. We also discuss the relevance of street canyon effects compared with background concentrations of these pollutants.     

The reciprocal relation between lightning and pollution and their impact over Kolkata, India

Aerosol loading in the atmosphere can cause increased lightning flashes, and those lightning flashes produce NO _X , which reacts in sun light to produce surface ozone. The present study deals with the effect of surface pollutants on premonsoon (April–May) lightning activity over the station Kolkata (22.65° N, 88.45° E). Seven-year (2004–2010) premonsoon thunderstorms data are taken for the study. Different parameters like aerosol optical depth and cloud top temperature from the Moderate Resolution Imaging Spectroradiometer satellite products along with lightning flash data from Tropical Rainfall Measuring Mission’s (TRMM) Lightning Imaging Sensor are analyzed. Some surface pollution parameters like suspended particulate matter, particulate matter 10, nitrogen oxides (NO _X ), and surface ozone (O₃) data during the same period are taken account for clear understanding of their association with lightning activity. Heights of convective condensation level and lifting condensation level are collected from radiosonde observations to anticipate about cloud base. It is found that increased surface pollution in a near storm environment is related to increased lightning flash rate, which results in increased surface NO _X and consequently increased surface ozone concentration over the station Kolkata.