Tropospheric ozone columns (TCOs) derived from differences between the Dutch-Finnish Aura Ozone Monitoring Instrument (OMI) measurements of the total atmospheric ozone column and the Aura Microwave Limb Sounder (MLS) measurements of stratospheric ozone columns are discussed. Because the measurements by these two instruments are not spatially coincident, interpolation techniques, with emphasis on mapping the stratospheric columns in space and time using the relationships between lower stratospheric ozone and potential vorticity (PV) and geopotential heights (Z), are evaluated at mid-latitudes. It is shown that this PV mapping procedure produces somewhat better agreement in comparisons with ozonesonde measurements, particularly in winter, than does simple linear interpolation of the MLS stratospheric columns or the use of typical coincidence criteria at mid-latitudes. The OMI/MLS derived tropospheric columns are calculated to be 4 Dobson units (DU) smaller than the sonde measured columns at mid-latitudes. Standard deviations between the derived tropospheric columns and those measured by ozonesondes are 9 DU (30%) annually but they are just 6 DU (15%) in summer. Uncertainties in the interpolated MLS stratospheric columns are likely to be the primary cause of these standard deviations. An important advantage of the PV mapping approach is that it works well when MLS data are missing (e.g., when an orbit of measurements is missing). In the comparisons against ozonesonde measurements, it provides up to twice as many comparisons compared to the other techniques. The OMI/MLS derived tropospheric ozone columns have been compared with corresponding columns based on the Tropospheric Emission Spectrometer (TES) measurements, and Regional chEmical trAnsport Model (REAM) simulations. The variability of tropospheric ozone columns has been examined for spring and summer 2005 over North America and the surrounding oceans. Comparisons of monthly mean distributions show good agreements between OMI/MLS tropospheric ozone columns, REAM columns, and TES columns. Two six-day periods in March have been selected to study the periodic TCO enhancements in two regions, around the Baja peninsula (Mexico) and over the West Coast of California. Thirteen-day back trajectories and daily maps of carbon monoxide (CO) and ozone from GEOS-CHEM and OMI/MLS have been used to investigate the influence of cross-Pacific transport. It is concluded that in the first period of the case study, the high ozone concentrations in mid and lower troposphere over the West Coast of California have been under the influence of cross-Pacific transport. Meteorological fields indicate that the high ozone concentrations in the upper troposphere over the West Coast of California and the high TCOs over the Baja peninsula are associated with stratospheric intrusions through a deep Rossby wave breaking event. The correlations between REAM TCOs and surface ozone from Environmental Protection Agency ground network measurements indicate that the TCO enhancement over the West Coast is associated with an increase of surface ozone. The correlations of REAM TCOs with geopotential height, wind fields, and tropopause height during the case study period suggest that TCO enhancement is best characterized in springtime by decreases of geopotential height on the 500 mb surface.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

L’ozone (O3) est un gaz reconnu comme un des polluants atmosphériques majeurs du XXIème siècle, de par ses propriétés très oxydantes. Dans les plus basses couches de notre atmosphère, ce polluant secondaire est produit par des réactions photochimiques impliquant des précurseurs émis par les activités humaines et la végétation. De nombreuses études expérimentales ont révélées le caractère phytotoxique de l’O3, qui dégrade sévèrement la photosynthèse, réduit le rendement des récoltes et inhibe la croissance des arbres. Afin de quantifier les effets de l’O3 sur les écosystèmes à l’échelle globale, des modèles numériques ont été développés. Dans cette thèse, nous avons principalement développé un nouveau modèle d’impact basé sur le concept dose/réponse au sein du modèle global de végétation ORCHIDEE. L’approche semi-mécaniste utilisée vise à représenter de manière simplifiée les effets du stress oxydatif causés par l’O3 sur la photosynthèse. L’étalonnage des paramètres a été réalisé en utilisant des données physiologiques issues majoritairement d’expériences de fumigation à l’air libre et en chambres à ciel ouvert menées pendant la saison de croissance de plusieurs espèces végétales. Cette étape de calibration a permis de déterminer les paramètres spécifiques à plusieurs types fonctionnels de plantes. La sensibilité du modèle à l’O3 et à son interaction avec le CO2 et le stress hydrique a ensuite été testée. A l’échelle locale, notre modèle d’impact reproduit fidèlement l’allure de la réponse de la photosynthèse observée in situ à l’échelle saisonnière, et l’élévation du CO2 compense partiellement l’impact de l’O3. En outre, le couplage entre la photosynthèse et la conductance stomatique dans ORCHIDEE permet de simuler la limitation des effets de l’O3 par les flux entrants. La fermeture stomatique réduit également la transpiration, ce qui augmente l’humidité du sol et préserve ainsi la végétation d’un stress hydrique accentué. Cependant, les effets observés sur la respiration autotrophe ne sont pas représentés et l’impact sur la surface foliaire est sous-estimé. Afin d’évaluer la performance du modèle, nous avons comparé l’impact simulé sur la productivité nette (NPP) annuelle avec l’effet estimé par les relations empiriques linéaires standards, recommandées par l’UNECE pour évaluer les risques phytotoxiques chez plusieurs types d’écosystèmes. En outre, à l’échelle globale, nous obtenons des résultats similaires aux estimations réalisées avec un autre modèle de végétation munie d’une paramétrisation d’impact différente. Enfin, nous estimons que les concentrations actuelles causent localement une chute de productivité nette totale annuelle allant jusqu’à 11.7% en moyenne dans le nord-est des Etats-Unis, et réduirait le contenu en carbone du sol de 10.9% dans cette région et de 42.5% en Indonésie si la pollution actuelle perdure pendant 50 ans. Ce travail indique que l’impact de l’O3 sur la végétation est non-négligeable dans le modèle ORCHIDEE, et doit être pris en compte dans les études globales du bilan de carbone terrestre. / Ozone (O3) is a gas recognized as a major atmospheric pollutant of the 21st century, due to its strong oxidant properties. As a secondary pollutant, O3 is produced by photochemical reactions between both anthropogenic and biogenic precursors. Numerous experimental studies have highlighted the phytotoxic effects of O3, which severely impairs photosynthesis, reduces crop yields and forest growth. Numerical models are used in order to quantify the impact of O3 at global scale. In this thesis, the major work was to develop a new parameterization based on the dose/response concept and to integrate it in the global vegetation model ORCHIDEE. We used a semi-mechanist approach to represent the effects of oxidative stress induced by O3 on photosynthesis. Parameters were obtained by comparing modelled and observed physiological variables related to free-air and open-top chamber fumigation experiments, carried out during the growing period for different plant species corresponding to several plant functional types in the model. Sensitivity tests were conducted to evaluate the influence of O3 and its interactive effects with CO2 and water-stress on the ecophysiological processes in ORCHIDEE. We reproduced the curvilinear response observed on photosynthesis at the leaf level during a growing season, and the elevation of CO2 concentration partially mitigates the O3 effect. The induced simulated stomatal closure slows down the impact on photosynthesis coupled to conductance by reducing the entering O3 fluxes. It also decreases transpiration and increases soil water content, which protects vegetation from higher water-stress. However, observed changes in autotrophic respiration are not simulated and the impact on foliar surface is underestimated. In order to evaluate the performance of our model, we compared the simulated impact on annual net primary productivity (NPP) with the empirical linear dose/response relationships recommended by UNECE to assess the risk for different types of ecosystems. Moreover, at global scale, we found results similar to those from another land surface model using a different impact relationship. Finally, we estimated that current O3 concentrations cause locally a decrease in total annual net productivity up to 11.7% on average in the north-west of USA, and could decrease the soil carbon content by 10.9% in this region and by 42.5% in Indonesia, if current O3 pollution remains the same for 50 years. This work confirms that impact of O3 on vegetation is non-negligible in the model ORCHIDEE, and must be considered in global carbon budget modelling.

No description available.

No description available.

Previous research has shown that there is considerable enhancement of tropospheric ozone over the African continent. The role of biomass burning as a source of ozone precursor gases and the atmospheric circulation, in particular the anticyclonic gyres over southern Africa, are known to be important in the accumulation of ozone over the subcontinent. In addition, the injection of ozone-rich air from the stratosphere is known to account for the occurrence of ozone peaks in the upper troposphere. This thesis is aimed at investigating the occurrence of high ozone events, defined as 2::100 ppbv, over Africa. Their variability in time (seasonal distribution) and space (latitudinal distribution) is quantified for the upper tropospheric region (~l 0 - 12 km) from 35°N to approximately 35°S . The data used are part of the MOZAIC (Measurement of OZone and wAter vapour by Airbus In-service airCraft) database. Ozone, water vapour. and temperature are measured at cruise altitude by these in-service aircraft, and this study explores data gathered on flights between Europe and Africa over the period January 1996 to December 1998. Complementary data from the European Centre for Medium Range Weather Forecasts (ECMWF) and satellite images are used to investigate case studies for selected flights in order to determine the origin of ozone episodes. Backward trajectory modeling is used to determine the source of air masses possibly related to ozone episodes. Correspondence with high potential vorticity and low water vapour content are used as stratospheric tracers and are indicative of stratospheric-tropospheric injection. Marked seasonal and latitudinal differences in the frequency and nature of ozone episodes are noted between the northern and southern latitudes. The seasonal variation of ozone episodes is more prominent in the extratropics than in the tropics. The highest frequencies are observed in the Northern Hemisphere to the north of 200N in spring and summer, and in the Southern Hemisphere to the south of 30°8 in winter and spring . Between these latitudes the distribution of peaks is sparse. An exception is observed during the austral spring when a relatively high number of peaks south of the equator is evident. The spring frequency peak is common to both hemispheres and is likely to result from a biomass burning influence, and stratospheric ozone injection into the troposphere during this season. Ozone peaks north of 15°N are greater in magnitude (up to 350 ppbv) than those in the tropics and in the Southern Hemisphere, where peaks do not exceed 200 ppbv. The horizontal extent of the ozone events ranged from a few tens of kilometers to over 1000 km in the boreal spring, although they seldom exceeded 100 km in the tropics. Two case studies were examined in detail. In the first case study, ozone peaks up to 180 ppbv were observed at approximately 12° S in the summer. They ranged between 3.5 and 21 km in horizontal extent and were accompanied by increased relative humidity and evidence of uplift. They were attributed to localized biomass burning and subsequent convective uplift to the upper troposphere. The possibility of enhancement due to convective uplift and lightning production was discussed. The second case study, in which an ozone peak of 287 ppbv was observed at approximately 31°S in springtime, had a horizontal extent of 840 km and was accompanied by low relative humidity values and high potential vorticity, indicative of air of stratospheric origin. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Pas de résumé en français / The present study was undertaken to investigate whether vacuolar endoproteolysis and/or protein carbonylation (measured here with a newly developed method) were functionally linked and if either of these processes or both could differentiate between ozone sensitive and tolerant wheat cultivars (cvs). Two winter wheat (Triticum aestivum L.) cvs released in 1986 (Soissons) and 2006 (Premio) were grown in the field and exposed to ambient and semi-controlled chronic ozone concentrations, from pre-anthesis to harvest, using a new linear ozone fumigation device that generates gradients of the pollutant. Grain yield and quality were more affected by the ozone treatments in the older cv Soissons that appeared to be the most sensitive. Because stomatal conductance did not differ significantly between the two cvs, differential ozone sensitivity was rather ascribed to differences in the biochemical and molecular responses between the two cvs. Ozone detrimental effects were mainly characterized by premature induction of leaf senescence, causing the shortening of the assimilation and grain-filling periods. Even though Soissons exhibited higher constitutive levels of carbonyl content in total soluble proteins, the increases in protein carbonylation, in response to the ozone treatments, were equivalent in both cvs. Thus basal levels of protein carbonyl seems a more relevant parameters to distinguish between ozone sensitive and tolerant wheat cvs than actual change in this parameter in response to ozone treatments. However, ozone induced more carbonyl groups on Rubisco large subunit (LSU) and small subunit (SSU) in Soissons and this was associated with a more pronounced decline in LSU and SSU contents and a lower Rubisco activity. Increased protein carbonyl levels and losses in total chlorophyll contents were concurrent, suggesting a link between the extent of oxidative stress and senescence development. Moreover, ozone treatments induced a stimulation of endoproteolytic activities that resulted mostly from increases in cysteine protease activities, for both cvs. Surprisingly, total proteolytic and cysteine protease activities were more enhanced in the tolerant cv, whereas elevated proteolysis is usually associated with high sensitivity to environemental stresses, like drought. Expression analysis for three genes encoding papain-like cysteine proteases showed poor correlation with total cysteine protease activities, which suggested that post-transcriptional regulation mechanisms were prevalent over transcriptional ones. Increased endoproteolytic activities were associated with increased protein carbonylation and with a decline in total soluble protein contents. Oxidized proteins could be more susceptible to proteolysis. Therefore, we suggest that ozone-induced ROS caused protein oxidation on one hand and acted as a signal that triggered senescence processes, such as enhanced proteolysis, on the other hand

No description available.

Industrial flaring can result in atmospheric emissions that have significant impact on regional air quality. This study investigates the impact on one-hour average ozone concentrations due to industrial flaring, using the region around Houston, Texas as a case study. Specifically, this study examined the impact on ozone formation of different flare destruction efficiencies. There are some concerns about whether flare destruction efficiency is reduced from design conditions (98 to 99% destruction) at low flare flow rates. Some studies have reported very low flares destruction efficiencies under low flow, so it is possible that ozone precursor emissions may be underestimated by an order of magnitude or more at low flow conditions. In this thesis, 100 different destruction efficiency scenarios have been constructed where destruction efficiency depends on the ratio of flare flow rate to the maximum flow rate (turndown ratio). The scenarios differ in the assumed destruction efficiency at near zero flow and the turndown ratio at which destruction efficiency returns to the design value. These destruction scenarios are applied to hourly mass flow data for twenty-five flares in Houston, Texas. The scenarios have very different impacts on air quality. The air quality implications of these results for possible modifications to flare operation are explored. / text