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PubMed1997

The effects of ozone on antioxidant responses in plants.

The response of plants to ozone exposure includes a number of physiological and biochemical changes that are the direct result of selective increases or decreases in gene expression and the resulting changes in the accumulation of the corresponding protein products. Major classes of ozone-induced proteins include antioxidant enzymes and a number of stress-related proteins associated with other biotic and abiotic stresses. In particular, there is a significant overlap in the pattern of gene induction observed in ozone-treated plants and plants exhibiting pathogen defense responses. Current knowledge concerning the specific molecular events associated with the alterations of gene expression caused by ozone and the precise roles of ozone-induced proteins in conferring tolerance to ozone is rather limited. This review summarizes some of the recent results that have been obtained concerning the molecular basis of ozone-induced responses in plants, with an emphasis on studies of the model plant system, Arabidopsis thaliana. These studies demonstrate that ozone-induced responses are caused in part by the activation of a salicylic acid dependent signaling pathway that is also required for the expression of resistance to microbial pathogens.

Antioxidants↗
PubMed1998

Ozone-induced airway hyperresponsiveness in patients with asthma: role of neutrophil-derived serine proteinases.

Proteinase inhibitors may be of potential therapeutic value in the treatment of respiratory diseases such as chronic obstructive pulmonary disease (COPD) or asthma. Our aim was to study the role of neutrophils, and neutrophil-derived serine proteinases in an acute model in patients with asthma. Exposure to ozone induces an acute neutrophilic inflammatory reaction accompanied by an increase in airway hyperresponsiveness. It is thought that these two effects of ozone are linked, and that neutrophil-derived serine proteinases (i.e. elastase) may play a role in the ozone-induced airway hyperresponsiveness. Therefore, we examined the effect of recombinant antileukoprotease (rALP), one of the major serine proteinase inhibitors in the lung, on ozone-induced changes in airway hyperresponsiveness in this model. We observed that 16 h after exposure to ozone, airway hyperresponsiveness to methacholine was increased both following placebo and rALP treatment. There was no significant difference between placebo and rALP treatment (change in area under the dose-response curve to methacholine: 117.3+/-59.0 vs 193.6+/-59.6 % fall x DD; p=.12). Moreover, the immediate decrease in FEV1 after ozone exposure was not significantly different between the two groups (placebo: -29.6+/-6.7%; rALP: -20.9+/-3.8%; p=.11). In addition, no significant differences were observed in plasma levels of fibrinogen degradation products generated by neutrophil serine proteinases before and after exposure to ozone. We conclude that neutrophil-derived serine proteinases are not important mediators for ozone-induced hyperresponsiveness.

Administration, Inhalation↗
PubMed2003

Selenium modifies glutathione peroxidase activity and glutathione concentration in mice exposed to ozone-provoked oxidative stress.

The aim of this study was to show the direct effect of selenium on glutathione peroxidase (GSH-Px) activity and GSH/GSSG concentrations in 3- and 6-month-old mice. An ozone-oxygen mixture was used to provoke an oxygen stress. To measure the Se-effect mice were gavaged with sodium selenite. GSH-Px activity and total glutathione concentrations were determined in serum and in the postnuclear fraction of liver and lungs. Additionally glutathione concentrations were determined in whole blood. Both ozone and selenium, administered separately, reduced GSH-Px activity in lungs of 6-month-old animals, while in young mice an opposite effect of Se was observed. Ozone administered jointly with Se did not influence GSH-Px activity in 6-month-old mice, while in young, 3-month-old mice, a stimulatory effect in lungs was observed. There were no significant changes in GSH-Px activity in the liver of 6-month-old mice, but the stimulatory effect occurred in young mice treated with Se and Se & ozone jointly. In young mice, ozone (also ozone with Se) augmented glutathione concentrations. The response to ozone and selenium strictly depended on age and the antagonism between selenium and ozone was observed only in a few cases.

Animals↗
PubMed2001

Bromate minimization during ozonation: mechanistic considerations.

Bromate formation during ozonation of bromide-containing natural waters is somewhat inversely connected to the ozone characteristics: an initial fast increase followed by a slower formation rate. During the initial phase mostly OH radical reactions contribute to bromate formation,whereas in the secondary phase both ozone and OH radicals are important. To minimize bromate formation several control options are presented: ammonia addition, pH depression, OH radical scavenging, and scavenging or reduction of hypobromous acid (HOBr) by organic compounds. Only the two first options are applicable in drinking watertreatment. By both methods a similar effect of a bromate reduction of approximately 50% can be achieved. However, bromate formation during the initial phase of the ozonation cannot be influenced by either method. Ammonia (NH3) efficiently scavenges HOBrto NH2Br. However, this reaction is reversible which leads to higher required NH3 concentrations than expected. The rate constant kNH2Br for the hydrolysis of NH2Br by OH- to NH3 and OBr- was found to be 7.5-10(6) M(-1) s(-1). pH depression shifts the HOBr/ OBr- equilibrium to HOBr and also affects the ozone chemistry. The effect on ozone chemistry was found to be more importantfor bromate formation. For a given ozone exposure, the OH radical exposure decreases with decreasing pH. Therefore, for pH depression the overall oxidation capacity for a certain ozone exposure decreases which in turn leads to a smaller bromate formation.

Ammonia↗
PubMed2001

Indoor chemistry: ozone and volatile organic compounds found in tobacco smoke.

The deliberate generation of ozone in indoor settings has been promoted as a method to reduce the concentration of indoor pollutants. The present study examines the effect of ozone on a subset of volatile organic compounds (VOCs) found in tobacco smoke. The decays of these compounds were measured in a static room-sized chamber: (1) in the absence of ozone, (2) in the presence of moderate ozone concentrations (< 0.115 ppm), and (3) in the presence of high ozone concentrations (< 1.4 ppm). At moderate ozone concentrations there was little effect on the monitored VOCs. At high ozone concentrations there was a small, unanticipated reduction in the concentration of some of the saturated VOCs, apparently caused by OH radicals produced as a consequence of the ozone/alkene reactions. There was also a much larger reduction in the concentrations of those compounds with unsaturated carbon bonds. However, this reduction was largely matched by an increase in the concentration of a number of aldehydes. Some of these aldehydes are more potent irritants than their precursors. Furthermore, even a relatively small ventilation rate (approximately 0.1 h-1) would produce a greater reduction in the monitored VOCs than that produced by a moderate amount of ozone.

Environmental Monitoring↗
PubMed2002

Effect of dissolved cobalt(II) on the ozonation of oxalic acid.

Cobalt(II) was examined as an ozonation catalyst. Laboratory-scale batch ozonation experiments were run at near-neutral pH and 24 degrees C. A hydroxyl radical probe compound, p-chlorobenzoic acid (pCBA), was also included in the solution matrix. Batch experiments showed that trace amounts of cobalt(II) accelerated the ozonation of oxalate. The rate of oxalate removal increased with decreasing pH from pH 6.7 to pH 5.3. The presence of cobalt(II) also increased the removal rate of pCBA indicating that the generation of hydroxyl radicals are byproducts of cobalt(II)-catalyzed ozonation of oxalate. It is proposed that the first step in the catalytic ozonation reaction pathway is the formation of a cobalt(II)--oxalate complex. Cobalt(II) oxalate is then oxidized by ozone to form cobalt(III) oxalate. The catalytic cycle is completed with decomposition of the cobalt(III) complex to form cobalt(II) and an oxalate radical. Assuming that cobalt, oxalate, and water were in equilibrium, the second-order reaction rate constants at pH 6 for ozonation of the cobalt(II) monooxalate and dioxalate species were 30 +/- 9 and 4000 +/- 500 M-1 s-1, respectively. These are both much greater than the reaction rate constant for the ozonation of free oxalate (kO3 < or = 0.04 M-1 s-1).

Catalysis↗
PubMed2002

Ozone interactions with carpet: secondary emissions of aldehydes.

Ozone-induced formation of aldehydes was studied on the surface and in the gas phase above carpets and on carpet components. Samples of four carpets were exposed to 100 ppb ozone. Emission rates of aldehydes and other organic compounds were measured from exposed and unexposed samples. Surface interactions of ozone with carpets produced C1-C13 n-aldehydes and several unsaturated aldehydes. Total aldehyde emission rates increased markedly with ozone exposure, from 1 to 70 microg m(-2) h(-1) for unexposed samples, to 60-800 microg m(-2) h(-1) during exposure. One exposed sample emitted large amounts of 2-nonenal (180-230 microg m(-2) h(-1)), a compound with a low odor threshold. Material balance modeling of a residence with this high emitting carpet suggests (1) that the concentration of 2-nonenal would be well above its odor threshold even in areas with only moderate ambient ozone levels and (2) that odorous levels of 2-nonenal could persist for years. Reactions of ozone with gas-phase primary emissions from carpet significantly reduced the levels of 4-phenylcyclohexene and produced small amounts of branched ketones. Separately measured patterns of aldehyde emissions from ozone exposure of linseed and tung oils were similar but not identical to those observed from ozone-exposed carpets.

Air Pollution, Indoor↗
PubMed2003

Photolysis of ozone in aqueous solutions in the presence of tertiary butanol.

The ozone decomposition quantum yield (phi) in millimolar and higher-concentration aqueous tertiary butanol solution is 0.64 +/- 0.05 (observed over a wavelength range from 250 to 280 nm) and rises toward lower tertiary butanol concentrations (phi approximately 1.5 at 10(-5) M at pH 2) on account of the onset of the well-known *OH-radical-induced chain reaction. The destruction of the organic is initiated by hydrogen-atom abstraction through OH radicals which are produced via the reaction of the photolytically generated O(1D) with the solvent water at a quantum yield of phi(*OH) of about 0.1. There is no decomposition of ozone in the dark on the time scale of the photolysis experiment. The efficiency of tertiary butanol destruction with respect to ozone consumption ([O3]0 = 3 x 10(-4) M), defined by the ratio delta[t-BuOH]/delta[O3], termed eta(t-BuOH), is 0.26 at millimolar tertiary butanol concentrations, determined at the stage of essentially complete ozone consumption. It diminishes toward lower tertiary butanol concentrations (delta[t-BuOH]/delta[O3] approximately 0.17 at [t-BuOH]0 = 1 x 10(-4) M). Part of the effect of the ozone, apart from being a source of *OH radicals, rests on the intervention of HO2*/O2*- which is produced in the course of the peroxyl-radical chemistry of the tertiary butanol in this dioxygen-saturated environment and converted into further *OH radical by reaction with ozone. Moreover in this system, organic free radicals and peroxyl radicals react with the ozone. On the basis of the experimental and mechanistic-simulation data, the quantum yield of direct (by hv) ozone cleavage in aqueous solution is estimated at about 0.5.

Hydroxyl Radical↗
PubMed2005

Products of ozone-initiated chemistry in a simulated aircraft environment.

We used proton-transfer-reaction mass spectrometry (PTR-MS) to examine the products formed when ozone reacted with the materials in a simulated aircraft cabin, including a loaded high-efficiency particulate air (HEPA) filter in the return air system. Four conditions were examined: cabin (baseline), cabin plus ozone, cabin plus soiled T-shirts (surrogates for human occupants), and cabin plus soiled T-shirts plus ozone. The addition of ozone to the cabin without T-shirts, at concentrations typically encountered during commercial air travel, increased the mixing ratio (v:v concentration) of detected pollutants from 35 ppb to 80 ppb. Most of this increase was due to the production of saturated and unsaturated aldehydes and tentatively identified low-molecular-weight carboxylic acids. The addition of soiled T-shirts, with no ozone present, increased the mixing ratio of pollutants in the cabin air only slightly, whereas the combination of soiled T-shirts and ozone increased the mixing ratio of detected pollutants to 110 ppb, with more than 20 ppb originating from squalene oxidation products (acetone, 4-oxopentanal, and 6-methyl-5-hepten-2-one). For the two conditions with ozone present, the more-abundant oxidation products included acetone/propanal (8-20 ppb), formaldehyde (8-10 ppb), nonanal (approximately 6 ppb), 4-oxopentanal (3-7 ppb), acetic acid (approximately 7 ppb), formic acid (approximately 3 ppb), and 6-methyl-5-hepten-2-one (0.5-2.5 ppb), as well as compounds tentatively identified as acrolein (0.6-1 ppb) and crotonaldehyde (0.6-0.8 ppb). The odor thresholds of certain products were exceeded. With an outdoor air exchange of 3 h(-1) and a recirculation rate of 20 h(-1), the measured ozone surface removal rate constant was 6.3 h(-1) when T-shirts were not present, compared to 11.4 h(-1) when T-shirts were present.

Air Pollution, Indoor↗
PubMed2005

Kinetics of aqueous ozone-induced oxidation of some endocrine disruptors.

This study investigated aqueous ozone-induced oxidation of six endocrine disruptors (EDs: 4-n-nonylphenol, bisphenol A, 17alpha-ethinylestradiol, 17beta-estradiol, estrone, and estriol). In the first part, ED ozonation kinetics were studied over a pH range of 2.5-10.5 at 20 +/- 2 degrees C and in the presence of tert-butyl alcohol. Under these conditions, for each studied compound, the apparent ozone rates presented minima at acidic pH (pH < 5) and maxima at basic pH (pH > 10). In the second part, to explain this pH dependence, elementary reactions, i.e., reactions of ozone with neutral and ionized ED species, were proposed, and the intrinsic constants of each of them were calculated. The reactivity of ozone with ionized EDs (i.e. 1.06 x 10(9)-6.83 x 10(9) M(-1) s(-1)) was found to be 10(4)-10(5) times higher than with neutral EDs (i.e. 1.68 x 10(4) M(-1) s(-1)-2.21 x 10(5) M(-1) s(-1)). At pH > 5, ozone reacted to the greatest extent with dissociated ED forms. Finally, to assess the potential of ozone for inducing ED oxidation in water treatment conditions, the expected removal rates for each of the studied EDs were determined on the basis of the kinetic study at pH = 7 and 20 +/- 2 degrees C. For all EDs considered, O3 exposures of only approximately 2 x 10(-3) mg min L(-1) were calculated to achieve > or = 95% removal efficiency. The ozonation process could thus highly oxidize the studied EDs under water treatment conditions.

Endocrine System↗
PubMed2004

Variation of surface ozone in the ambient air of Auckland, New Zealand.

A study has been performed on the characteristics and behavior of surface ozone concentrations at four monitoring sites in Auckland, New Zealand (37 degrees S, 174.8 degrees E) for a four-year period (October 1997-October 2001). One monitoring site (rural) was located upwind of the Auckland urban complex, a second downwind (rural-coastal), and a third within the urban area, while the fourth was an elevated urban-city site located 250 m up the Sky Tower in the central city. In contrast to the high elevation site, the diurnal behaviour of ozone at the three low elevation sites followed a typical solar radiation cycle with high ozone during the day and low nocturnal values. The effect of NO(x) titration was distinct at the urban sites. There was also a seasonal variability in the measured ozone levels with high concentrations in spring and a significant summer minimum. The observed surface ozone concentrations in Auckland were significantly lower than other cities of the world, although a potential for high oxidant formation existed. Observed ozone episodes appear to have been either generated locally or the precursors transported via the prevailing southwest wind. A unique feature of Auckland's air quality is the dilution of polluted city air due to the mixing of east-coast air into the clean west-coast circulation leading to the overall lower average concentrations in summer. A second feature is the potential interaction between sea salt particles and ozone that may provide an additional ozone loss mechanism.

Air Pollutants↗
PubMed2003

Sensory evaluation of emissions from selected building products exposed to ozone.

The interaction of ozone with eight different building products was studied in test chambers. The products were plasterboard, two types of paints on plasterboard, two types of carpet, linoleum, pinewood, and melamine-covered particleboard. Four months of conditioning prior to the experiment had left the products with a low emission. The products' ability to remove ozone from the air covered a wide range. For three of the products (plasterboard with paint, carpet, and pinewood), it was shown that the removal was primarily due to interactions in the products' surfaces and only to a minor extent due to gas-phase reactions. Sensory evaluations were carried out for five of the products, with different ozone-removal potentials. A sensory panel assessed the emissions from sets of two specimens of each product; one specimen was exposed to a high, but realistic, ozone concentration (10 or 80 ppb) and one specimen was exposed to no ozone (background level < 3 ppb). The panel assessed odor intensity and was asked to choose which odor of the two specimens they preferred. The perceivable changes in emissions due to exposure of the products to ozone depended on the type of product. The greatest effect was seen for carpet. Carpet was the only product that showed significantly higher odor intensity when exposed to ozone. Besides, the effect of ozone on preference was strongest for carpet and resulted in a clear negative sensory evaluation. A similar but less pronounced effect was seen for pinewood and plasterboard with paint. No clear preference was seen for melamine and linoleum.

Construction Materials↗
PubMed2002

Airway function, oedema, cell infiltration and nitric oxide generation in conscious ozone-exposed guinea-pigs: effects of dexamethasone and rolipram.

1. The effects of ozone inhalation (90 min, 2.15+/-0.05 p.p.m.) and their modification by dexamethasone (20 mg kg(-1)) or the phosphodiesterase-4 inhibitor, rolipram (1 mg kg(-1)), administered (i.p.) 24 and 0.5 h before and 24 h after ozone exposure were examined in conscious guinea-pigs. 2. Ozone caused an early-phase bronchoconstriction (EPB) as a fall in specific airways conductance (sG(aw)) measured by whole body plethysmography, followed at 5 h by a late-phase bronchoconstriction (LPB) and increased respiratory rate. Rolipram did not alter this profile but dexamethasone inhibited the EPB. 3. Airway hyperreactivity to inhaled histamine (1 mM, 20 s) occurred at 0.5, 2, 12, 24 and 48 h after ozone inhalation, the 2 h change being abolished by rolipram and dexamethasone. 4. Bronchoalveolar lavage fluid (BALF) macrophages, eosinophils and neutrophils were significantly (P<0.05) elevated at 12, 24 and 48 h after ozone exposure, the 48 h influx being significantly attenuated (P<0.05) by rolipram and dexamethasone. 5. BALF nitric oxide (NO) metabolites decreased 0.5 h after ozone exposure by 52%, recovered at 2 h and significantly increased at 12 (101%) and 24 h (127%). The elevated NO was unaffected by rolipram or dexamethasone. 6. Lung oedema, measured from wet/dry weight differences, was significant 12, 24 and 48 h after ozone exposure, the latter being significantly attenuated (P<0.05) by rolipram and dexamethasone. 7. Ozone exposure of guinea-pigs produced features common to COPD. Although rolipram and dexamethasone did not affect the airway function changes, they inhibited the inflammation, airway hyperreactivity and oedema.

Animals↗
PubMed2002

Effect of ozone exposure on allergic sensitization and airway inflammation induced by dendritic cells.

BACKGROUND: Epidemiological studies suggest that ozone exposure is related to increased asthma symptoms. Dendritic cells (DCs) are the principal antigen-presenting cells in the airways. OBJECTIVE: We have examined whether ambient doses of ozone (100 ppb for 2 h) enhance allergic sensitization and/or airway inflammation in a mouse model. METHODS: C57BL/6 mice were sensitized to inhaled ovalbumin (OVA) by intratracheal instillation of OVA-pulsed DCs on day 0. Daily exposure to OVA aerosol on days 14-20 resulted in an eosinophilic airway inflammation, as reflected in bronchoalveolar lavage fluid and lung histology. In a first experiment, mice were exposed to ozone or room air immediately prior to and following sensitization. Subsequently, we tested the effect of ozone exposure during antigen challenge in DC-sensitized mice. RESULTS: Exposure to ozone during sensitization did not influence airway inflammation after subsequent allergen challenge. In contrast, in sensitized mice, challenge with OVA together with ozone (days 14-20) resulted in enhanced airway eosinophilia and lymphocytosis, as compared with mice exposed to OVA and room air (1.91 x 106 +/- 0.46 x 106 vs. 0.16 x 106 +/- 0.06 x 106 eosinophils/mL lavage fluid; P = 0.015; 0.49 x 106 +/- 0.11 x 106 vs. 0.08 x 106 +/- 0.03 x 106 lymphocytes/mL lavage fluid; P = 0.004). Ozone exposure without subsequent OVA exposure did not cause airway inflammation. CONCLUSION: Ozone exposure does not increase allergic sensitization but enhances antigen-induced airway inflammation in mice that are sensitized via the airways.

Air Pollutants↗
PubMed2001

Effect of ozone on neutrophil function in vitro.

The application of ozone is widely practised as a form of alternative medicine, particularly in Germany and Eastern Europe. Ozone major autohemotherapy (the return of a small amount of a patient's blood to the circulation after ex vivo exposure to ozone) has been reported to have a therapeutic effect in various pathological conditions, including ischemic, infectious, autoimmune and neoplastic disorders. Ozone has an effect on the expression of cytokines, adhesion molecules and acute phase reactants, which are responsible in part for the respiratory inflammatory response observed after exposure to this gas. The purpose of the present study was to investigate the effect of ozone administration ex vivo, at a concentration commonly used in major autohemotherapy, on peripheral blood neutrophil function in vitro. Blood drawn from healthy volunteers was studied for neutrophil adhesion, chemotaxis and O-2 production before and after exposure to 30 microg/ml ozone. There was no significant difference in adhesion and chemotaxis of neutrophils exposed to ozone versus unexposed cells. O-2 production was minimally decreased (20.3 +/- 5.0 vs. 22.1 +/- 5.5 nmol/106 cells/10 min, respectively; P=0.01), a reduction of no clinical significance. This study confirms that major autohemotherapy with ozone is safe as far as neutrophil function is concerned. Combined with previous data, it seems that well-designed clinical trials to assess the efficacy of major autohemotherapy would pose no danger to blood cell populations, and should be encouraged.

Adult↗
PubMed1997

Pre-activating wounding response in tobacco prior to high-level ozone exposure prevents necrotic injury.

In tobacco, both wounding and treatment with jasmonates prior to exposure of the tissue to high concentrations of ozone (250 to 500 p.p.b.) produce a dramatic decrease in ozone injury. A systemic pattern of increased ozone tolerance developed within 3-6 h after wounding and also after local application of jasmonates. Ozone treatment of transgenic (NahG) tobacco plants showed that the inability of these plants to accumulate salicylic acid is also accompanied by increased ozone tolerance. Expression of mRNA encoding the anti-oxidant enzyme ascorbate peroxidase is upregulated by ozone challenge, wounding and by methyl jasmonate exposure within 3-4 h, while levels of carbonic anhydrase mRNA are simultaneously depressed following ozone exposure and methyl jasmonate treatment. The pattern of these results shows that the response to ozone challenge in tobacco involves signalling mechanisms similar to those induced in plants by other environmental stresses that generate reactive oxygen species.

Acetates↗
PubMed2004

[Ozone decline and UV increase].

The following results have been obtained from long-term observations on the ozone layer and UV at the Meteorological Observatory Hohenpeigenberg:The seasonally varying decline of the ozone layer determines the maximum exposure to UV. Since ozone decline shows the highest rates in the spring months the UV exposure has most strongly increased in this time of the year. This is especially important because in spring the human skin is not adapted to UV exposure. Weather changes from day to day can induce rapid ozone reductions in spring about -30% which in turn is followed by an increase in UV of about 40%. Clouds, especially the transparent cirrus clouds (high clouds consisting of ice particles) have increased in frequency during spring and fall while a decrease is observed in summer. This change in cloudiness reduces the daily UV dose in spring and fall while it is enhanced in summer. With increasing height above sea level UV rises by roughly 10% per 1000 m (rule of thumb). Snow reflects the UV-radiation by up to 80% enhancing the UV-doses at relevant conditions. Strong volcano eruptions destroy ozone in the stratosphere additionally during 1-2 years after the eruption. Therafter the ozone layer recovers. In April 1993, after the eruption of Mt. Pinatubo (1991), the UV burden was still 40% higher than average. Miniholes and streamers can appear unexpected on a short-time scale and cross over Central Europe within 1-2 days, thus enhancing UV irradiation. The human skin reacts to UV exposure depending on the type of skin. The campaign "Sonne(n) mit Verstand" of the Bavarian Ministries for Environment, for Health and for Education informs about the danger of UV radiation (see www.sonne-mit-ver-stand.de). The German Weather Service informs the public on present developments of the ozone layer and relevant topics byits ozone bulletin, which is also available via internet under (www.dwd.de/deFundE/Observator/MOHp/hp2/ozon/bulletin.htm).

Climate↗
PubMed2003

Long-term variation in surface ozone and its precursors in Athens, Greece: a forecasting tool.

INTENTION, GOAL, SCOPE, BACKGROUND: Photochemical pollution is a very complex process involving meteorological, topographic, emission and chemical parameters. The most important chemical mechanisms involved in the atmospheric process have already been identified and studied. However, many unknown parameters still exist because of the large number of participating chemical reactions. OBJECTIVE: The present study investigates the processes involved in the photochemical pollution effect of an urban station located in the greater area of the Athens basin and gives a plausible explanation for the different seasonal ozone development between that station and another rural one. Furthermore, the distribution of the mean monthly surface ozone observed at the urban station during 1987-2001 is examined in order to create a relevant forecasting tool. METHODS: Averaged hourly data of O3 and NOx observations monitored at the above mentioned stations, during 1987-2001, have been used in order to derive the daytime (7:00-15:00) values. Trajectories calculated by using a 2D-trajectory code and meteorological data, during the period 1988-1996, have also been used. RESULTS AND DISCUSSION: At the urban station, the percentage negative trend of NO and NOx data in winter and summer is higher than that in spring and autumn, while the percentage ozone trend is maximum in the summer. On the contrary, the negative surface ozone trend at the rural station exhibits a minimum in summer and a maximum in autumn and winter. The mean seasonal wind-rose for the selected months shows that the northward wind flow dominates during June, the month of the lowest negative ozone trend in the rural station. Finally, the development of the forecasting tool shows that the mean monthly surface ozone data during the period (1987-2001) demonstrates a semi-log distribution. CONCLUSIONS: Air transport effect on the air pollution of the rural station (not blocked by mountains) is deduced as a possible reason for the different seasonal ozone development observed between the rural and the urban station. Finally, the discrepancies between the theoretical probabilities deduced by the model and the empirical ones appear to be very small, and the corresponding correlation coefficient is 0.99. RECOMMENDATION AND OUTLOOK: However, to interpret the aforementioned statistical results about the negative trends in ozone and its precursors, additional parameters can be taken into account. Changes in NOx concentrations, for instance, can result not only from changes in emissions or meteorological conditions. There might also be a contribution through changes in the atmospheric composition. A study of the contribution of changes in atmospheric composition to trends of observed NOx concentrations requires that a series of steps be taken (removal of meteorological influence in the time series, calculation of trends in OH concentrations, etc.).

Air Movements↗