Biogenic volatile organic compounds (BVOC) are a wide-ranging group of trace gas components in the atmosphere which are emitted naturally from Earth’s surface. It is now recognised that biogenically sourced VOCs are far more significant on a global scale than those from anthropogenic sources, with up to 10 times greater emissions. Very few field-based studies of fluxes from plant canopies have been undertaken, particularly for non-terpenoid compounds. This thesis presents mixing ratio and flux measurements of BVOC from a range of temperate plant canopies: Douglas fir, short-rotation coppice willow, Miscanthus and mixed peatland vegetation. The virtual disjunct eddy covariance technique (vDEC) using a proton transfer reaction mass spectrometer (PTR-MS) as a fast VOC sensor was used for all measurements except for peatlands, where grab samples were collected on adsorbent sampling tubes for later chromatographic analysis. The PTR-MS was also utilised for measuring the rate of degradation of VOCs during laboratory chamber experiments. Mixing ratios and fluxes of VOCs measured within and above a Douglas fir forest were the first canopy-scale measurements for this species. Fluxes of monoterpenes were comparable to previous studies while isoprene was also detected (standard emissions factors up to 1.15 μg gdw -1 h-1 and 0.18 μg gdw -1 h-1, respectively). Emissions of oxygenated VOCs were also found to be significant, highlighting the importance of quantifying a wider variety of VOCs from biogenic sources, other than isoprene and monoterpenes. Results for bioenergy crops Miscanthus and willow showed that willow was a high isoprene emitter (20 μg gdw -1 h-1), but no measureable VOCs were detected from Miscanthus. This indicates that future expansion of bioenergy crops, and hence species selection, should take resultant air quality and human health impacts – due to changing VOC emissions – into account. Fluxes of BVOC from a Scottish peatland are the first reported measurements for this ecosystem in a temperate climate. Additionally, to assess the impact of nitrogen deposition on VOC fluxes, BVOC measurements were taken from sample plots in a pre-existing, long-term field manipulation study to assess impacts of wet nitrate or ammonium deposition on peatland. The peatland was found to be a significant source of isoprene and monoterpenes (590 and 1.5 μg m-2 h-1 respectively) and there was evidence that emissions were affected by wet nitrogen treatment. Isoprene emissions were reduced by both nitrate and ammonium treatment, while nitrate increased β- pinene fluxes. Increasing atmospheric nitrogen concentrations are therefore predicted to have an impact on VOC emission. Chamber studies showed that the rate of loss of α-pinene from the gas-phase during oxidation – and hence potential formation of secondary organic aerosol (SOA) – decreased with increasing isoprene mixing ratio. This was not observed for limonene. These results show that as isoprene mixing ratios increase with increasing global temperatures, negative feedback on radiative forcing from SOA particles may be suppressed. Results from this thesis provide valuable experimental data for a range of temperate plant canopies, which will help constrain modelled predictions of future VOC emissions. Additionally, the importance of understanding the effects of land use and environmental change on VOC emissions was demonstrated.

A atmosfera terrestre contém nitrogênio e oxigênio, sendo este último, um composto altamente reativo e fundamental ao desenvolvimento e manutenção da vida. Além desses gases, diversos outros compostos em pequenas concentrações, os quais podem atuar como reagentes e/ou catalisadores também a compõe. Os compostos gasosos variados e material particulado (orgânico e inorgânico) de diferentes dimensões lançados constantemente à atmosfera são provenientes de fontes diversas. Tais fontes podem ser de origem natural ou antrópica e ainda, podem ser pontuais, difusas, primárias, secundárias, móveis e/ou estacionárias. Os processos envolvendo transformações químicas na atmosfera são extremamente importantes porque tendem a manter a sua composição em estado estacionário. A vegetação, que constitui uma fonte natural, é responsável pela emissão de grandes quantidades de compostos carbonados para a atmosfera. Dentre os vários compostos orgânicos emitidos da superfície do planeta, destacam-se em particular, alguns gases traços, denominados compostos orgânicos voláteis (COVs). A emissão dos compostos orgânicos voláteis pela vegetação ocorre, em escala global, predominantemente nos trópicos ou nos meses de verão em outras regiões. As reações fotoquímicas dos compostos orgânicos voláteis desempenham um papel diferenciado e importante na química da troposfera, podendo alterar de forma significativa a concentração de ozônio em áreas tanto urbanas quanto rurais. O presente projeto contempla o estudo de alguns dos inúmeros compostos orgânicos voláteis de origem biogênica (COVBs) emitidos pela vegetação constituinte, das regiões da Floresta Amazônica, da Mata Atlântica e da floresta Tropical da Guiana Francesa, comparando-se os dados de saída gerados pelos Modelos MOZART-4 e CAM-Chem. A escolha dos sítios experimentais para realização deste estudo se deu em parte em função da importância dos locais em termos de biodiversidade, extensão territorial, influência na climatologia (local e/ou regional), bem como também em função da acessibilidade, proximidade a centros urbanos e alterações devido à influência humana. O procedimento metodológico adotado para coleta das amostras de COVBs se deu por meio da técnica conhecida como acumulação de vórtices turbulentos (Relaxed Eddy Accumulation - REA), a qual faz uso de um dispositivo coletor denominado acumulador compacto de vórtices turbulentos (Compact Relaxed Eddy Accumulator - CREA). As amostras gasosas de COVBs foram coletadas por meio de cartuchos comerciais apropriados, compostos por diferentes materiais adsorvedores que apresentavam afinidade química também diferenciada para os variados compostos aos quais foram expostos. Estudos primários para determinação da natureza dos cartuchos que foram utilizados neste projeto foram realizados, a fim de se obter dispositivos adequados a este propósito. Os resultados evidenciam, como esperado, que a presença de isopreno é predominante em todos os sítios experimentais, sendo sua concentração média diária máxima de 5,0 ± 0,3 μg/cm3 registrada na Amazônia e de 8,0 ± 0,4 μg/cm3 (concentração diária) na floresta da Guiana Francesa, seguido pelo alfa-pineno cuja concentração máxima obtida foi de aproximadamente 1,6 ± 0,08 μg/cm3 no último sítio experimental, ambos detectados na estação seca. A emissão de isopreno e dos monoterpenos ocorreu de forma mais acentuada na época seca em comparação ao período úmido. Contudo, observou-se em algumas situações uma pequena discrepância. De maneira geral os resultados gerados pelos modelos estão subestimados, como exceção do parâmetro de radiação fotossinteticamente ativa (PAR), o que indica que a defasagem entre os resultados observados e os simulados pode estar relacionada parâmetros de OH-, NOx e em algumas reações químicas fotoquímicas envolvendo o ozônio. / The Earth\'s atmosphere contains nitrogen and oxygen, the last one being a highly reactive compound and fundamental to the development and maintenance of life. Besides these gases, many other compounds in small concentrations, which can act as reactants and /or catalysts can be found in the atmosphere. Various gaseous compounds and particulate matter (organic and inorganic) of different dimensions constantly released into the atmosphere come from various sources. Such sources can be natural or anthropogenic and still be punctual, diffuse, primary, secondary, mobile and or stationary. Processes involving chemical transformations in the atmosphere are extremely important because they tend to maintain their steady-state composition. The vegetation, which is a natural source, is responsible for producing large amounts of carbon compounds in the atmosphere. Among the various organic compounds emitted from the planet\'s surface, stand out in particular, some trace gases, called volatile organic compounds (VOCs). The emission of volatile organic compounds by vegetation occurs on a global scale, predominantly in the tropics or in the summer months in other regions. The photochemical reactions of volatile organic compounds play an important and unique role in the chemistry of the troposphere, which can significantly change the concentration of ozone in both urban and rural areas. This project involves the study of some of the numerous biogenic volatile organic compounds (BVOC) emitted by vegetation from the Amazon Forest, the Mata Atlântica forest and the Tropical forest of French Guiana, comparing the output data generated by MOZART -4 and CAM-Chem models. The choice of experimental sites for this study was in part due to the importance of local biodiversity , territorial extent , influence the weather (local and/or regional), and also because of accessibility, proximity to urban centers and changes due to human influence . The methodological procedures for collecting samples of VOCs was through the technique known as eddy accumulation (Relaxed Eddy Accumulation - REA), which uses an equipment known as compact relaxed eddy accumulator (CREA). The gas samples were collected from BVOCs through appropriate commercial cartridges, composed of different materials showed that chemical affinity adsorbents also differentiated for the various compounds which were exposed. Primary studies to determine the nature of cartridges that were used in the field campaigns were conducted in order to obtain devices suitable for this purpose. The results show, as expected, the presence of isoprene as a prevalent compound in all experimental sites, with maximum daily average concentration of 5,0 ± 0,3 μg/cm3 registered on the Amazon basin and 8,0 ± 0,4 μg/cm3 (daily concentration) in the forest of French Guiana, followed by alpha-pinene, whose maximum concentration obtained was approximately 1,6 ± 0,08 μg/cm3 in the last experimental site, both detected in the dry season. The emission of isoprene and monoterpenes occurred sharply in the dry season compared to the wet season. However, it was observed in some situations a small discrepancy. In general, the results generated by the models are underestimated, as an exception of photosynthetically active radiation parameter (PAR), indicating that the gap between the observed and simulated results can be related to OH- and NOx parameters and some chemical reactions involving photochemical ozone.

A atmosfera terrestre contém nitrogênio e oxigênio, sendo este último, um composto altamente reativo e fundamental ao desenvolvimento e manutenção da vida. Além desses gases, diversos outros compostos em pequenas concentrações, os quais podem atuar como reagentes e/ou catalisadores também a compõe. Os compostos gasosos variados e material particulado (orgânico e inorgânico) de diferentes dimensões lançados constantemente à atmosfera são provenientes de fontes diversas. Tais fontes podem ser de origem natural ou antrópica e ainda, podem ser pontuais, difusas, primárias, secundárias, móveis e/ou estacionárias. Os processos envolvendo transformações químicas na atmosfera são extremamente importantes porque tendem a manter a sua composição em estado estacionário. A vegetação, que constitui uma fonte natural, é responsável pela emissão de grandes quantidades de compostos carbonados para a atmosfera. Dentre os vários compostos orgânicos emitidos da superfície do planeta, destacam-se em particular, alguns gases traços, denominados compostos orgânicos voláteis (COVs). A emissão dos compostos orgânicos voláteis pela vegetação ocorre, em escala global, predominantemente nos trópicos ou nos meses de verão em outras regiões. As reações fotoquímicas dos compostos orgânicos voláteis desempenham um papel diferenciado e importante na química da troposfera, podendo alterar de forma significativa a concentração de ozônio em áreas tanto urbanas quanto rurais. O presente projeto contempla o estudo de alguns dos inúmeros compostos orgânicos voláteis de origem biogênica (COVBs) emitidos pela vegetação constituinte, das regiões da Floresta Amazônica, da Mata Atlântica e da floresta Tropical da Guiana Francesa, comparando-se os dados de saída gerados pelos Modelos MOZART-4 e CAM-Chem. A escolha dos sítios experimentais para realização deste estudo se deu em parte em função da importância dos locais em termos de biodiversidade, extensão territorial, influência na climatologia (local e/ou regional), bem como também em função da acessibilidade, proximidade a centros urbanos e alterações devido à influência humana. O procedimento metodológico adotado para coleta das amostras de COVBs se deu por meio da técnica conhecida como acumulação de vórtices turbulentos (Relaxed Eddy Accumulation - REA), a qual faz uso de um dispositivo coletor denominado acumulador compacto de vórtices turbulentos (Compact Relaxed Eddy Accumulator - CREA). As amostras gasosas de COVBs foram coletadas por meio de cartuchos comerciais apropriados, compostos por diferentes materiais adsorvedores que apresentavam afinidade química também diferenciada para os variados compostos aos quais foram expostos. Estudos primários para determinação da natureza dos cartuchos que foram utilizados neste projeto foram realizados, a fim de se obter dispositivos adequados a este propósito. Os resultados evidenciam, como esperado, que a presença de isopreno é predominante em todos os sítios experimentais, sendo sua concentração média diária máxima de 5,0 ± 0,3 μg/cm3 registrada na Amazônia e de 8,0 ± 0,4 μg/cm3 (concentração diária) na floresta da Guiana Francesa, seguido pelo alfa-pineno cuja concentração máxima obtida foi de aproximadamente 1,6 ± 0,08 μg/cm3 no último sítio experimental, ambos detectados na estação seca. A emissão de isopreno e dos monoterpenos ocorreu de forma mais acentuada na época seca em comparação ao período úmido. Contudo, observou-se em algumas situações uma pequena discrepância. De maneira geral os resultados gerados pelos modelos estão subestimados, como exceção do parâmetro de radiação fotossinteticamente ativa (PAR), o que indica que a defasagem entre os resultados observados e os simulados pode estar relacionada parâmetros de OH-, NOx e em algumas reações químicas fotoquímicas envolvendo o ozônio. / The Earth\'s atmosphere contains nitrogen and oxygen, the last one being a highly reactive compound and fundamental to the development and maintenance of life. Besides these gases, many other compounds in small concentrations, which can act as reactants and /or catalysts can be found in the atmosphere. Various gaseous compounds and particulate matter (organic and inorganic) of different dimensions constantly released into the atmosphere come from various sources. Such sources can be natural or anthropogenic and still be punctual, diffuse, primary, secondary, mobile and or stationary. Processes involving chemical transformations in the atmosphere are extremely important because they tend to maintain their steady-state composition. The vegetation, which is a natural source, is responsible for producing large amounts of carbon compounds in the atmosphere. Among the various organic compounds emitted from the planet\'s surface, stand out in particular, some trace gases, called volatile organic compounds (VOCs). The emission of volatile organic compounds by vegetation occurs on a global scale, predominantly in the tropics or in the summer months in other regions. The photochemical reactions of volatile organic compounds play an important and unique role in the chemistry of the troposphere, which can significantly change the concentration of ozone in both urban and rural areas. This project involves the study of some of the numerous biogenic volatile organic compounds (BVOC) emitted by vegetation from the Amazon Forest, the Mata Atlântica forest and the Tropical forest of French Guiana, comparing the output data generated by MOZART -4 and CAM-Chem models. The choice of experimental sites for this study was in part due to the importance of local biodiversity , territorial extent , influence the weather (local and/or regional), and also because of accessibility, proximity to urban centers and changes due to human influence . The methodological procedures for collecting samples of VOCs was through the technique known as eddy accumulation (Relaxed Eddy Accumulation - REA), which uses an equipment known as compact relaxed eddy accumulator (CREA). The gas samples were collected from BVOCs through appropriate commercial cartridges, composed of different materials showed that chemical affinity adsorbents also differentiated for the various compounds which were exposed. Primary studies to determine the nature of cartridges that were used in the field campaigns were conducted in order to obtain devices suitable for this purpose. The results show, as expected, the presence of isoprene as a prevalent compound in all experimental sites, with maximum daily average concentration of 5,0 ± 0,3 μg/cm3 registered on the Amazon basin and 8,0 ± 0,4 μg/cm3 (daily concentration) in the forest of French Guiana, followed by alpha-pinene, whose maximum concentration obtained was approximately 1,6 ± 0,08 μg/cm3 in the last experimental site, both detected in the dry season. The emission of isoprene and monoterpenes occurred sharply in the dry season compared to the wet season. However, it was observed in some situations a small discrepancy. In general, the results generated by the models are underestimated, as an exception of photosynthetically active radiation parameter (PAR), indicating that the gap between the observed and simulated results can be related to OH- and NOx parameters and some chemical reactions involving photochemical ozone.

Emissions from natural ecosystems, broadly classified as biogenic volatile organic compounds (BVOCs), contribute 90\% to the VOC budget. Individual BVOCs vary widely in their reaction rates with atmospheric oxidants, making their atmospheric impact highly dependent on VOC composition. Their emissions are also dependent on vegetative make up and a number of meteorological and ecological variables. However, the ecological and physical drivers of their emissions is becoming more variable in a changing climate, leading to greater uncertainties in models. Increasing the monitoring of individual compounds can improve our understanding of the drivers of these emissions and the impact of individual chemical species on atmospheric composition. Improved understanding of BVOC composition can better emission models and, SOA and ozone formation predictions. To study the atmospheric impacts and physical drivers of BVOCs, a GC-FID was adapted for automated hourly sampling and analysis. The details of the hardware and software used for the system are described in detail to enable future long-term BVOC measurements in additional locations. The instrument was deployed at a measurement tower in a forest in central Virginia for year-round collection of BVOC concentrations. Using two years of collected hourly data, this work assesses the chemical impacts of individual BVOCs on time scales ranging from hour to year. This work identifies the importance of both concentration and chemical structure in determining atmospheric impacts. Additionally, seasonality in the concentration of some biogenic species has large implications for atmospheric reactivity in the warmest months of the year, particularly ozone reactivity. Using ecological and meteorological data collected at the site in conjunction with the BVOC data, the drivers of BVOC concentrations and their seasonality are identified. Comparison between this data and current models, reveal important deviations which may lead to large modeled uncertainties. Furthermore, the collected data has been made publicly available to aid in future research regarding BVOCs. / Doctor of Philosophy / The earth hosts a number of sources of atmospheric emissions. These range from human-driven sources such as vehicles and factories, to natural sources such as trees and grass. The content of these emissions, amongst others, become a part of a large reactor (the atmosphere), that interact with each other. The interaction of these emissions with atmospheric oxidants forms a gas (ozone) with implications for human and ecosystem health, and secondary organic aerosol (the leading component to smog). However, the extent to which these emissions react with atmospheric oxidants is largely dependent on the structure of individual compounds. A major focus of this dissertation is to show that compounds with reactive structures can have a large impact on atmospheric composition, and that the quantity of emissions can be as important as compound structure. Understanding the impact of individual compounds in the atmosphere requires improved measurement techniques, capable of detecting the compounds of interest over long time periods. Therefore, another focus of this work was the adaptation and deployment of an instrument capable of detecting some of the most reactive species in the atmosphere, volatile organic compounds emitted from forests. The instrument deployed in this work was a gas chromatography flame ionization detector (GC-FID), which detects compounds largely composed of carbon and hydrogen. The instrument was adapted to run automatically through the development of an electronics box and software program interfaced with the GC-FID. Following development, the instrument was deployed to a remote forest research site for two years. The data collected from this work was used to determine the impact of individual compounds on atmospheric composition. Findings from this work could be used to improve a range of atmospheric models. Small changes in emissions (human or plant) contribute to the total VOC budget which can have large implications for the formation of ozone and SOA. Therefore, increased understanding of the BVOC concentrations and emission driver will aid in predicting these atmospheric components.

La réactivité totale OH est la perte totale du radical hydroxyle (le principal oxydant de l'atmosphère) avec les gaz réactifs dans l'air ambiant. Elle représente la mesure de la quantité totale des réactifs dans un environnement donné.Nous présentons ici un travail expérimental se concentrant sur les améliorations techniques d'une méthode appelée "Comparative Reactivity Method" pour mesurer la réactivité OH su le terrain ainsi que sur des résultats obtenus sur deux sites ciblés dans le bassin méditerranéen.La réactivité OH mesurée était élevée dans les deux sites. Sur le site récepteur en Corse (France) au cours de l'été 2013, nous avons observé que la réactivité OH était en moyenne de 5,5 s-1 (avec un maximum de 17 s-1). Ces mesures ont été comparées avec les observations de composés en phase gazeuse réalisées pendant la campagne. Il a été noté que pendant une période de la campagne, seulement 50% de la réactvité était expliqué par les mesures complémentaires.Lors de mesures dans une forêt de chênes pubescents, émetteurs isoprène, dans le sud de la France, nous avons observé que la réactivité OH maximale était très élevée (69 s-1), en accord avec la réactivité calculée à partir des mesures des gaz réactifs.Ce travail de thèse met en évidence que: (i) le bassin méditerranéen est un fort émetteur de gaz réactifs, (ii) la réactivité mesurée dans ces deux sites de la Méditerranée a été fortement impactée par les émissions biogéniques, (iii) il reste encore beaucoup de composés inconnus associés aux émissions biogéniques primaires et secondaires. A l'avenir, plusieurs approches pourraient etre utilisées pour identifier ces composés inconnus: en couplant la mesure de la réactivité OH avec des mesures de plantes dans des enceintes fermées (composés primaires), études en chambre de vieillissement (composés primaires et secondaires), ainsi que des approches de modélisation. / The total OH reactivity is the total loss rate of the hydroxyl radical with the reactive gases in ambient air. It represents the measure of the total loading of reactants in a given environment.Here we present an experimental work focusing on the technical improvements of the Comparative Reactivity Method to measure the OH reactivity on the field and field measurements of OH reactivity at two targeted sites in the Mediterranean basin.The measured OH reactivity was high at both sites. At a receptor site in Corsica (France) during summer 2013, we observed that the OH reactivity was maximum 17 s-1, on average 5.5 s-1 and during one week only 50% was explained by the complementary measurements in the gas phase.At a forest of downy oak trees, high isoprene emitters, in the south of France, we observed that the OH reactivity was maximum 69 s-1, in agreement with the reactivity calculated from the measurements of reactive gases only during daytime.This thesis work highlights that: (i) the Mediterranean basin is a strong emitter of reactive gases, (ii) the reactivity measured in these two sites in the Mediterranean was strongly impacted by the biogenic emissions, (iii) there are still many unknowns associated to measures of biogenic volatiles primary emitted and secondary produced. Such unknowns might be reduced in the future by coupling the measurement of the OH reactivity with plants enclosures and chambers studies as well as modelling approaches.

Biogenic volatile organic compounds (VOCs) react with Cl and OH radicals and the resulting radicals combine with oxygen to form peroxy radicals RO2. Organic peroxy radicals can then react with NO to form NO2, a precursor of tropospheric ozone. The work presented here explored the initial reaction between Cl and thujone, a VOC emitted by Great Basin sagebrush. The rate constant for the reaction of thujone + Cl at 296 K was measured with the method of relative rates with FTIR for detection of reactants. LEDs were used to photolyze Cl2 to generate Cl in the reaction cell. Thujone was also photolyzed by the LEDs and therefore the relative rates model was revised to account for this photolysis. With toluene as the reference compound, the rate constant for thujone + Cl at 296 K is 2.62 ± 1.90 × 10-12 molecules-1 s-1, giving an atmospheric lifetime of 0.5--2.6 minutes for thujone. Cline et al. showed that the rate of the self-reaction of HO2CH2CH2O2 (β-HEP) increases in the presence of water vapor. This enhancement has a strong temperature dependence with a greater enhancement observed at colder temperatures. The observed rate enhancement has been attributed to the formation of a β-HEP--H2O complex. In this work, the equilibrium constant for the formation of the β-HEP--H2O complex was calculated by ab initio calculations. Given the energy available at room temperature, the complex will populate three local minimum geometries and β-HEP will populate two local minimum geometries. The partition function for each of these geometries was calculated and used to calculate the equilibrium constant for complex formation as a function of temperature. Based on these computational results, the observed temperature dependence for the rate enhancement can be attributed to the strong temperature dependence for the rate constant of the reaction of β-HEP--H2O + β-HEP rather than the temperature dependence of complex formation.

Thesis (MSc) -- Macquarie University, Division of Environmental and Life Sciences, Dept. of Chemistry and Biomolecular Sciences, 2008. / Bibliography: p. 120-124. / Introduction -- Environmental factors affecting the emission of biogenic Volatile organic compounds -- Materials and experimental procedures -- Quantification using sold-phase microextraction in a dynamic system: technique development -- The emission profile of Tristaniopsis laurina -- Study of the effect of elevated atmospheric CO₂ levels on the emission of BVOCS from Australian native plants -- Conclusions and future work. / Biogenic Volatile Organic Compounds (BVOCs) emitted by plants can affect the climate and play important roles in the chemistry of the troposphere. As ambient atmospheric carbon dioxide (CO₂) levels are rapidly increasing knowledge of the effect of elevated atmospheric CO₂ on plant BVOC emissions is necessary for the development of global climate models. -- During this study, the effect of elevated atmospheric CO2 mixing ratios on BVOC emissions from Corymbia citriodora (Lemon Scented Gum) and Tristaniopsis laurina (Water Gum) was determined for the first time through the combination of Solid-Phase Microextraction (SPME), Gas Chromatography-Flame Ionisation Detection (GC-FID), Gas Chromatography-Mass Spectrometry (GC-MS) and an environment chamber. For C. citriodora elevated atmospheric CO₂ led to a decrease in the emission rate of α-pinene, β-pinene, eucalyptol, citronellal and β-caryophyllene, however, elevated CO₂ had no effect on the emission rate of citronellol. The emission profile of T. laurina has been determined for the first time. For T. laurina elevated CO₂ led to a decrease in the emission rate of α-pinene but the emission rates of β-pinene, limonene, eucalyptol and citronellol were unaffected. The results obtained in this work confirm that the effect of elevated atmospheric CO₂ on plant BVOC emissions is species-specific. / Mode of access: World Wide Web. / 124 leaves ill. (some col.)

Les Composés Organiques Volatils biogènes (COVB) sont des molécules issues du métabolisme secondaire des végétaux, dont l'émission peut être modulée par les conditions environnementales. Parmi ces composés, l'isoprène a été très étudié du fait des flux d'émission important et de son implication dans la photochimie troposphérique. Cependant, les mécanismes d'action des facteurs environnementaux sont encore mal connus, et notamment celui de l'impact du stress hydrique. Dans le contexte de changements climatiques, ce type de stress va particulièrement impacter la région méditerranéenne.Nous avons étudié l'impact du stress hydrique sur les émissions d'isoprène de Quercus pubescens Willd. Cette espèce, très présente dans cette région, serait la seconde source d'isoprène en Europe.Deux étude ont été menées.La première, effectuée en pépinière, a consisté à appliquer un stress hydrique modéré et sévère d'avril à octobre. Une augmentation des émissions d'isoprène des arbres modérément stressés a été observée alors qu'il n'y a eu aucune modification des émissions pour les arbres très stressés.La seconde a consisté à faire un suivi saisonnier du stress hydrique au sein d'une chênaie pubescente. Un stress hydrique amplifié a été appliqué par un système d'exclusion de pluie, permettant de diminuer la quantité de pluie de 30%. Nous avons observé que le stress hydrique amplifié augmentait les facteurs d'émission d'isoprène des arbres.Cette base de données a permis le développement, par Réseau de Neurones Artificiels (RNA), d'un algorithme d'émission d'isoprène. Nous avons ainsi mis en évidence l'impact prédominant du contenu en eau du sol sur les émissions d'isoprène. / Biogenic Volatile Organic Compounds (BVOC) are plants secondary-metabolism-molecules. Their emissions are modulated by environmental conditions. Among these compounds, isoprene has been particularly studied due to its intense emission fluxes as well as its major contribution to tropospheric photochemistry. However, the impacts of environmental constraints on isoprene emission are still not yet well known. In particular, water stress impact is still a contradictory issue. In a world facing multiple climatic changes, models expect this kind of stress to hit Mediterranean area.This work focused on the impact of water stress on Quercus pubescens Willd. isoprene emissions. This species, widely spread in this area, is the second isoprene emitter in Europe.Two types of study were used.First, during an experimental carried out in a nursery, Q. pubescens saplings were grown under a moderate and severe water stress from April to October. This experimentation highlighted an increase of isoprene emissions for mid-stressed trees, while no emission changes were observed for the highly stressed trees.Secondly, an experimentation was conducted on a pubescent oak forest with trees acclimated to long lasting stress periods. We followed, during a whole season, the impact, on isoprene emissions, of a water stress created by artificially reducing 30% of the rains by means of a specific deploying roof. Isoprene emission factors were observed to increase under water stress.The database thus obtained was used in an Artificial Neural Network (ANN) to develop an appropriate isoprene emission algorithm. We underlined the predominant impact of soil water content on isoprene emissions.

Dans cette thèse, nous présentons des travaux complémentaires conduits à ICARE-CNRS (Orléans), partie A et à l’Université de Fudan (Shanghai), partie B. Partie A : les 2-et 3-carène sont deux composés organiques volatils biogéniques importants présents dans l’atmosphère dont les voies de dégradation sont encore mal connues. Afin de déterminer les constantes de vitesse des réactions de ces espèces avec l’ozone, nous avons utilisé trois systèmes expérimentaux complémentaires : des chambres de simulation d’ICARE de 7300L et 80000L (HELIOS) et un réacteur à flux laminaire. Les rendements de certains produits de réactions, le radical hydroxyle (OH), le formaldéhyde (HCHO) et le monoxyde de carbone (CO) ont aussi été déterminés. D’autre part, pour avoir une meilleure compréhension d’intermédiaires de réaction formés lors de l’ozonolyse, appelés intermédiaires de Criegee, un réacteur à flux laminaire à deux étages a été mis en place pour mesurer leurs constantes de vitesse de réaction avec SO2, NO2 et O3. Partie B : les impacts du “black carbon (BC)” et du “brown carbon (BrC)” constituent une incertitude majeure dans les modèles climatiques actuels. Des rapports récents indiquent que la morphologie et l’évolution des BC et BrC dans l’atmosphère jouent un rôle important sur la capacité d’absorption de ces particules. Afin d’étudier leurs comportements, des mélanges de particules (BC-BrC) ont été exposés en chambre de simulation atmosphérique à l'acide sulfurique, au mélange ammoniac / triéthylamine, et à la vapeur d'eau de manière séquentielle. / In this thesis, we present a complementary work conducted at ICARE-CNRS (Orléans), Part A and at Fudan University (Shanghai), Part B. Part A: 2-and 3-carene are two important biogenic volatile organic compounds present in the atmosphere. The knowledge on their degradation pathways and the corresponding products are still poor. Using complementary reaction systems-ICARE 7300 L and HELIOS 80000 L simulation chambers, vertical laminar flow reactor, their kinetic rate constants for reaction with ozone were determined. Additionally, important product formation yields, hydroxyl radical (OH), formaldehyde (HCHO) and carbon monoxide (CO) have been determined with indication to their corresponding formation routes from the ozonolysis of carene. To have a better understanding on reactions of Criegee intermediates (CIs) generated through ozonolysis in the atmosphere, a horizontal 2-stage laminar flow reactor was set up to measure the rate constants of CIs with SO2, NO2 and O3. Part B: Radiative forcing of black carbon (BC) in the atmosphere, as well as that of brown carbon (BrC), remains to be a major uncertainty in current climate models. Recent reports indicate that the absorption enhancement of BC and BrC particles is determined by evolution of morphology and mixing state during the atmospheric processing. Laboratory-generated BC-BrC mixture particles (BC-BrC) were exposed to sulfuric acid, ammonia/triethylamine, and water vapor sequentially to investigate the alternation in light absorption, morphology and mixing state during simulated atmospheric processing.

La pollution atmosphérique liée aux aérosols organiques secondaire (SOA) représente un des enjeux majeurs du XXIème siècle. La photochimie multiphasique des SOA constitue le coeur et l'originalité de cette thèse.Le réacteur photochimique permet de simuler en laboratoire, l'oxydation en phase aqueuse atmosphérique des composés organiques volatils biogéniques (BVOC), et notamment, la méthyl vinyl cétone (MVK), afin d'étudier la formation ces SOA.Nous étudions la réactivité de la MVK en présence de ●OH et sa capacité à oligomériser en fonction des concentrations initiales de MVK, d'oxygène, et de ●OH. Une large stratégie analytique basée sur la chromatographie liquide couplée à la spectrométrie de masse (MS) permet d'identifier des produits de réaction, et d'établir un mécanisme réactionnel, expliquant la formation des oligomères, leurs rendements et leur vieillissement.Les données colligées servent d'entrées à un modèle de boîte multiphasique, afin d'explorer la sensibilité de l'oligomérisation aux conditions atmosphériques.Ensuite, nous comparons la réactivité de la MVK en présence de ●OH à celle induite par la photolyse de l'acide pyruvique; puis nous mesurons la tension de surface engendrée par ces deux systèmes d'oligomères. Enfin, la mobilité ionique couplée à la MS permet d'observer la co-oligomérisation d'une gamme étendue de BVOC en présence de ●OH.L'oligomérisation atmosphérique implique (i) une concentration minimale de précurseurs pouvant être atteinte dans les aérosols humides via la co-oligomérisation; (ii) une réactivité en compétition avec l'oxygène dissous dans la phase aqueuse, et dont la pertinence atmosphérique reste à explorer. / Air pollution caused by secondary organic aerosol (SOA) is one of the major challenges of this century. We focus this thesis on SOA , through an innovative approach, i.e. multiphase photochemistry.The photochemical reactor allows to simulate in laboratory, the atmospheric aqueous phase oxidation of biogenic volatile organic compounds (BVOC) and in particular, methyl vinyl ketone (MVK), and thus, to study SOA.We study the reactivity of MVK in the presence of ●OH and its ability to oligomerize under various initial concentrations of oxygen, MVK and ●OH. A wide analytical strategy based on liquid chromatography-mass spectrometry is used to identify the reaction products, and establish a chemical mechanism. We focus on these oligomers systems, formation, yield and aging. Collected data are used as inputs to a multiphase box model to explore the sensitivity of oligomerization to the variations of physical and chemical atmospheric parameters. The photochemistry of pyruvic acid generates radical chemistry and initiates MVK oligomerization. We closely compare this reaction to MVK ●OH oxidation. Then, we measure the surface activity of both systems. The ability of oligomers to partition to the interface could affect the climate. Finally, we used ion mobility - mass spectrometry to observe ●OH co-oligomerization of a mixture of organic compounds most representative of the atmosphere.Atmospheric oligomerization implies (i) a minimal concentration of precursors that could be reached in wet aerosol via the co-oligomerization; (ii) a reactivity in competition with the addition of the dissolved oxygen, whose the atmospheric relevance remains to be explored.