Auswahl der wissenschaftlichen Literatur zum Thema „Photolyse – Atmosphère“
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Zeitschriftenartikel zum Thema "Photolyse – Atmosphère":
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Röckmann, T., S. Walter, B. Bohn, R. Wegener, H. Spahn, T. Brauers, R. Tillmann, E. Schlosser, R. Koppmann und F. Rohrer. „Isotope effect in the formation of H<sub>2</sub> from H<sub>2</sub>CO studied at the atmospheric simulation chamber SAPHIR“. Atmospheric Chemistry and Physics 10, Nr. 12 (16.06.2010): 5343–57. http://dx.doi.org/10.5194/acp-10-5343-2010.
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Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in the SAPHIR atmosphere simulation chamber under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only an indirect effect and cannot be effectively constrained. The molecular channel kinetic isotope effect KIEmol, the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) at surface pressure, is determined to be KIEmol=1.63−0.046+0.038. This is similar to the kinetic isotope effect for the total removal of HCHO from a recent relative rate experiment (KIEtot=1.58±0.03), which indicates that the KIEs in the molecular and radical photolysis channels at surface pressure (≈100 kPa) may not be as different as described previously in the literature.
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Epstein, S. A., und S. A. Nizkorodov. „A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase“. Atmospheric Chemistry and Physics Discussions 12, Nr. 4 (19.04.2012): 10015–58. http://dx.doi.org/10.5194/acpd-12-10015-2012.
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Abstract. Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. We find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.
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Cataldo, Franco, Giovanni Strazzulla und Susana Iglesias-Groth. „UV photolysis of polyynes at λ=254 nm and at λ>222 nm“. International Journal of Astrobiology 7, Nr. 2 (April 2008): 107–16. http://dx.doi.org/10.1017/s147355040800414x.
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AbstractFor the first time the kinetic rate constants of the UV photolysis of polyynes C6H2, C8H2, C10H2, C12H2 and C14H2 under rigorously inert atmosphere have been determined in three different solvents: n-hexane, n-heptane and decalin. First- or pseudofirst-order kinetics appear suitable to describe the photolysis of these molecules and k values in the range between 3.0×10−3 s−1 and 4.6×10−3 s−1 have been determined. The unique exception is represented by C6H2 which photolyses more slowly with k=3.2×10−4 s−1. Two different UV sources have been used in the present study: a low-pressure mercury lamp having a monochromatic emission at 253.7 nm and a medium-to high-pressure lamp with a continuous emission between 222 nm and 580 nm. The results are of interest in the understanding, and also the modelling, of the fate of polyynes released by carbon-rich stars in the interstellar medium or the polyynes released by comets in their active phase.
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Epstein, S. A., und S. A. Nizkorodov. „A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase“. Atmospheric Chemistry and Physics 12, Nr. 17 (12.09.2012): 8205–22. http://dx.doi.org/10.5194/acp-12-8205-2012.
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Abstract. Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. For example, we find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.
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Gálvez, Óscar, M. Teresa Baeza-Romero, Mikel Sanz und Alfonso Saiz-Lopez. „Photolysis of frozen iodate salts as a source of active iodine in the polar environment“. Atmospheric Chemistry and Physics 16, Nr. 19 (12.10.2016): 12703–13. http://dx.doi.org/10.5194/acp-16-12703-2016.
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Abstract. Reactive halogens play a key role in the oxidation capacity of the polar troposphere. However, sources and mechanisms, particularly those involving active iodine, are still poorly understood. In this paper, the photolysis of an atmospherically relevant frozen iodate salt has been experimentally studied using infrared (IR) spectroscopy. The samples were generated at low temperatures in the presence of different amounts of water. The IR spectra have confirmed that, under near-ultraviolet–visible (UV–Vis) radiation, iodate is efficiently photolysed. The integrated IR absorption coefficient of the iodate anion on the band at 750 cm−1 has been measured to be A = 9.8 ± 0.5 × 10−17 cm molecule−1. The photolysis rate of the ammonium iodate salt was measured by monitoring the decay of ammonium or iodate IR bands (1430 and 750 cm−1 respectively) in the presence of a solar simulator. The absorption cross section of the liquid solutions of ammonium iodate at wavelengths relevant for the troposphere (250 to 400 nm) has been obtained and used to estimate the photolytic quantum yield for the frozen salt. Finally, using an atmospheric model, constrained with the experimental data, we suggest that the photolysis of iodate in frozen salt can potentially provide a pathway for the release of active iodine to the polar atmosphere.
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Watanabe, Yasuto, und Kazumi Ozaki. „Relative Abundances of CO2, CO, and CH4 in Atmospheres of Earth-like Lifeless Planets“. Astrophysical Journal 961, Nr. 1 (01.01.2024): 1. http://dx.doi.org/10.3847/1538-4357/ad10a2.
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Abstract Carbon is an essential element for life on Earth, and the relative abundances of major carbon species (CO2, CO, and CH4) in the atmosphere exert fundamental controls on planetary climate and biogeochemistry. Here we employed a theoretical model of atmospheric chemistry to investigate diversity in the atmospheric abundances of CO2, CO, and CH4 on Earth-like lifeless planets orbiting Sun-like (F-, G-, and K-type) stars. We focused on the conditions for the formation of a CO-rich atmosphere, which would be favorable for the origin of life. Results demonstrated that elevated atmospheric CO2 levels trigger photochemical instability of the CO budget in the atmosphere (i.e., CO runaway) owing to enhanced CO2 photolysis relative to H2O photolysis. Higher volcanic outgassing fluxes of reduced C (CO and CH4) also tend to initiate CO runaway. Our systematic examinations revealed that anoxic atmospheres of Earth-like lifeless planets could be classified in the phase space of CH4/CO2 versus CO/CO2, where a distinct gap in atmospheric carbon chemistry is expected to be observed. Our findings indicate that the gap structure is a general feature of Earth-like lifeless planets with reducing atmospheres orbiting Sun-like (F-, G-, and K-type) stars.
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Gálvez, O., M. T. Baeza-Romero, M. Sanz und A. Saiz-Lopez. „Photolysis of frozen iodate salts as a source of active iodine in the polar environment“. Atmospheric Chemistry and Physics Discussions 15, Nr. 19 (15.10.2015): 27917–42. http://dx.doi.org/10.5194/acpd-15-27917-2015.
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Abstract. Reactive halogens play a key role in the oxidation capacity of the polar troposphere. However, sources and mechanisms, particularly those involving active iodine, are still poorly understood. In this paper, the photolysis of an atmospherically relevant frozen iodate salt has been experimentally studied using infrared (IR) spectroscopy. The samples were generated at low temperatures in the presence of different amounts of water. The IR spectra have confirmed that under near-UV/Vis radiation iodate is efficiently photolyzed. The integrated IR absorption coefficient of the iodate anion on the band at 750 cm−1 has been measured to be A = 9.5 × 10−17 cm molec−1. Using this value, a lower limit of the integrated absorption cross section of iodate, in an ammonium frozen salt, has been estimated for the first time at wavelengths relevant for tropospheric studies (σ = 1.1 × 10−20 cm2 nm molec−1 from 300 to 900 nm). According to this, we suggest that the photolysis of iodate in frozen salt can potentially provide a pathway for the release of active iodine to the polar atmosphere.
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Peacock, Sarah, Travis S. Barman, Adam C. Schneider, Michaela Leung, Edward W. Schwieterman, Evgenya L. Shkolnik und R. O. Parke Loyd. „Accurate Modeling of Lyα Profiles and Their Impact on Photolysis of Terrestrial Planet Atmospheres“. Astrophysical Journal 933, Nr. 2 (01.07.2022): 235. http://dx.doi.org/10.3847/1538-4357/ac77f2.
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Abstract Accurately measuring and modeling the Lyα (Lyα; λ1215.67 Å) emission line from low-mass stars is vital for our ability to build predictive high energy stellar spectra, yet interstellar medium (ISM) absorption of this line typically prevents model-measurement comparisons. Lyα also controls the photodissociation of important molecules, like water and methane, in exoplanet atmospheres such that any photochemical models assessing potential biosignatures or atmospheric abundances require accurate Lyα host star flux estimates. Recent observations of three early M and K stars (K3, M0, M1) with exceptionally high radial velocities (>100 km s−1) reveal the intrinsic profiles of these types of stars as most of their Lyα flux is shifted away from the geocoronal line core and contamination from the ISM. These observations indicate that previous stellar spectra computed with the PHOENIX atmosphere code have underpredicted the core of Lyα in these types of stars. With these observations, we have been able to better understand the microphysics in the upper atmosphere and improve the predictive capabilities of the PHOENIX atmosphere code. Since these wavelengths drive the photolysis of key molecular species, we also present results analyzing the impact of the resulting changes to the synthetic stellar spectra on observable chemistry in terrestrial planet atmospheres.
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Osajima, Josy Anteveli, Carla Cristina Schmitt Cavalheiro und Miguel Guillermo Neumann. „Changes in Molecular Weight of Poly(Styrenesulfonate) Initiated by Thioxanthone: Photolysis and Photo-Oxidation“. Materials Science Forum 869 (August 2016): 346–49. http://dx.doi.org/10.4028/www.scientific.net/msf.869.346.
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The presence of dyes in colored polymers can cause a series of reactions that promote their photodegradation under irradiation. The aim of this study was to investigate the kinetic behavior of the photodegradation of poly (sodium 4-styrenesulfonate) (PSS) in aqueous solution or in the presence of thioxanthone (TX) under UV radiation in different atmospheres. These systems were monitored by SEC. The polydispersity decreased in all systems studied indicating that there was a breach of the polymer main chain. Only the PSS / TX / air atmosphere system peaked, which occured at 43h of irradiation. However, this system showed slower kinetics of polymeric scission due to the dye suppressing a transfer of energy from the triplet state to the polymer. The photodegradation of solutions of PSS / air atmosphere showed higher efficiency under ultraviolet radiation in relation to the PSS in the presence or absence of the dye under an inert atmosphere.
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Moortgat, Geert K. „Important photochemical processes in the atmosphere“. Pure and Applied Chemistry 73, Nr. 3 (01.01.2001): 487–90. http://dx.doi.org/10.1351/pac200173030487.
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Among the many important roles played by ozone in the atmosphere is the role it plays in the generation of OH radicals, which are responsible for initiating the oxidation of a wide variety of atmospheric trace constituents. The OH production occurs dominantly from the formation of the excited O(1D) species in the UV photolysis of ozone, followed by the reaction of O(1D) with H2O vapor. The photochemistry of ozone is very complex, as the relatively weak bonds in ozone allow different states of the O and O2 photoproducts to be accessed. Recent detailed studies have now revealed that different photolysis channels are occurring in the 290375 nm spectral range, the region of importance for the generation of OH radicals in the lower atmosphere. The measured temperature-dependent quantum yields for the production of O(1D) atoms reflect the importance of the longer "wavelength tail" formation with regard to the enhanced OH production. Other significant atmospheric photolysis processes involving carbonyl compounds are reported. Direct photodissociation rates were measured in the outdoor photoreactor EUPHORE in Valencia and compared with model calculations. For most of the carbonyl compounds the effective quantum yields are significantly below unity.
Dissertationen zum Thema "Photolyse – Atmosphère":
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Romanzin, Claire. „Étude des processus de photolyse du méthane dans le cadre du programme SET UP (Simulations Expérimentales et Théoriques Utiles à la Planétologie) : application à l’atmosphère de Titan“. Paris 12, 2007. http://www.theses.fr/2007PA120083.
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Titan, satellite de Saturne présente la particularité de posséder une atmosphère dense au sein de laquelle se développe une chimie organique riche initie��e principalement par la dissociation de l’azote et du méthane atmosphériques. Pour étudier les processus photochimiques qui y sont rencontrés, un réacteur photochimique est en cours de développement au LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques). Il s’agit du projet SET UP (Simulations Expérimentales et Théoriques Utiles à la Planétologie). Ce projet prévoit de dissocier le méthane par photolyse multiphotonique à 248 nm (5 eV) au moyen d’un laser excimère. Ce processus de photolyse étant différent de celui responsable de la dissociation de CH4 sur Titan – absorption d’un photon à 121,6 nm (10,2 eV) – mon travail a consisté à réaliser une étude comparative de la photolyse de CH4 à 121,6 nm et 248 nm. La nature et l’abondance des fragments primaires issus de la photolyse de CH4, en particulier le fragment CH, mais aussi des molécules stables issues de leur recombinaison ont ainsi été étudiées à la fois expérimentalement et théoriquement. Différents types d’analyse ont été mises en œuvre : spectroscopie IRTF (Infra-Rouge à Transformée de Fourier), spectroscopies laser LIF (Laser Induced Fluorescence) et CRDS (Cavity Ring Down Spectroscopy). Les expériences utilisant la technique de détection CRDS ont été réalisées au LPPM (Laboratoire de Photophysique Moléculaire, Orsay) dans le cadre d’une collaboration. L’ensemble des résultats obtenus nous amènent à conclure que les fragments formés suite à la photolyse de CH4 à 121,6 nm et 248 nm sont vraisemblablement différentsSaturn’s biggest satellite, Titan, is the only one to exhibit a dense and chemically rich atmosphere. Its complex atmospheric chemistry is mainly initiated by the dissociation of atmospheric nitrogen and methane. In order to study the photochemical processes occuring on Titan, a photochemical reactor is being developed by the LISA laboratory. In this project, called SET UP (Experimental and Theoretical Simulations Useful for Planetology), methane is planned to be photodissociated by means of multiphotonic photolysis at 248 nm (5 eV). This photolytic process is different from the one responsible for CH4 photolysis on Titan i. E. The absorption of one photon at 121,6 nm (10,2 eV). Thus, the aim of my thesis work is to perform a comparative study of CH4 photolysis at 121,6 nm and 248 nm. The nature and abundance of the primary fragments arising from CH4 photolysis – especially the CH fragment – and of the stable molecules resulting from the subsequent chemistry have been studied both experimentally and theoretically. FTIR (Fourier Transform Infra-Red) spectroscopy and laser spectroscopy techniques such as LIF (Laser Induced Fluorescence) and CRDS (Cavity Ring Down Spectroscopy) have been employed as experimental techniques. The CRDS experiments have been performed in the LPPM laboratory as a collaboration. The different results obtained lead us to the conclusion that the fragments issued from CH4 photolysis at 121,6 and 248 nm are presumably different
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Bartolomei, Vincent. „Etude de la chimie de l'acide nitreux (HONO) pour les atmosphères intérieures“. Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4707.
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Du fait de l’omniprésence de l’homme au sein du compartiment intérieur, y passant jusqu’à 90% de son temps au cours d’une journée, il est devenu essentiel de caractérisé correctement l’atmosphère et donc les polluants présent dans ce milieu. Ce travail de thèse prend la suite d’une étude menée au sein de notre laboratoire montrant une importante présence de radicaux hydroxyles dans cette atmosphère. Le polluant précurseur des radicaux supposé au cours de cette étude est l’acide nitreux (HONO), présent dans des quantités de l’ordre du ppb pour l’intérieur. Ce travail de thèse a donc eu pour but, dans un premier temps de caractériser la photolyse de l’acide nitreux conduisant à la formation de radicaux hydroxyles, et dans un second temps d’établir ses différentes voies de formation, directes et indirectes, afin de quantifier ses sources dans les atmosphères intérieuresPeople in Western societies spend about 90% of their time indoors, predominantly within indoor places. The residence time of the airborne indoor pollutants is much longer due to the smaller volumes compared to the outdoor atmosphere and low air exchange rates. Therefore, a comprehensive understanding of indoor air quality is essential.Nitrous acid (HONO) is an emerging indoor pollutant because 1) it can lead to human respiratory tract irritation and formation of carcinogenic nitrosamines, and 2) it can be effectively photolyzed leading to a pulse of hydroxyl radicals (OH).The PhD work here presented is focused on understanding of the formation processes of oxidizing species such as HONO and, hence, OH radicals in the built environment
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Socorro, Joanna. „Etude de la réactivité hétérogène de pesticides adsorbés sur des particules modèles atmosphériques : cinétiques et produits de dégradation“. Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4769/document.
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Les pesticides sont un sujet d’actualité suscitant de nombreuses interrogations. Lors de leur épandage, une partie des pesticides sont émis dans l’atmosphère, important vecteur de dissémination. Ils se répartissent dans les différentes phases de l’atmosphère dont notamment la phase particulaire par la multiplication des usages de pesticides semi-volatils. Ils s’adsorbent à la surface des particules atmosphériques et sont soumis à des processus photochimiques régissant leur devenir. Actuellement, les estimations de la dégradation atmosphérique des pesticides ne prennent en compte que la phase gazeuse. Afin d’appréhender leur devenir et leurs impacts sur la santé et l’environnement, la réactivité hétérogène de 8 pesticides (cyprodinil, deltaméthrine, difénoconazole, fipronil, oxadiazon, pendiméthaline, perméthrine et tétraconazole) adsorbés à la surface de particules modèles a été étudiée. Ce travail s’est centré sur la détermination des temps de vie de ces 8 pesticides en présence d’humidité vis-à-vis du rayonnement solaire, de l’ozone (O3) et des radicaux hydroxyles (OH). Pour un ensoleillement moyen, les temps de vie en phase particulaire varient de 1 à 68 jours. Pour une concentration moyenne de 40 ppb d’O3 et de 10^6 molécule.cm^-3 en radicaux OH, les temps de vie sont respectivement compris entre 8 et plus de 35 jours et entre 24 à plus de 54 jours. La réactivité en phase particulaire est donc beaucoup plus lente qu’en phase gazeuse et confirme la nécessité de prendre en compte cette phase. Par l’identification des produits de dégradation, des mécanismes réactionnels mettent en évidence la formation de composés potentiellement plus toxiques que leurs précurseursPesticides represent a topic which raise an important number of questions. During their application, one fraction of the pesticides is emitted in the atmosphere, an important dissemination vector. In the atmosphere, pesticides are partitioned between different phases. However, due to increased use of semi-volatile pesticides, they are mostly enriched in the atmospheric particulate phase. They are adsorbed on the surface of atmospheric particles and undergo photochemical processes which govern the fate of pesticides in the atmosphere. Currently, the atmospheric fate of pesticides is based only on gas-phase reactivity. In order to properly understand the fate of pesticides and their impact on human health and on the environment, heterogeneous reactivity of 8 pesticides (cyprodinil, deltamethrin, difenoconazole, fipronil, oxadiazon, pendimethalin, permethrin and tetraconazole) adsorbed on the surface of silica particles, is evaluated. This work deals with the determination of lifetimes of these 8 pesticides under solar light irradiation, ozone (O3) and hydroxyl radicals (OH), in presence of humidity. With a daily average sunshine, the lifetimes of the pesticides in the particle phase are between ca. 1 day and 68 days. For an average mixing ratio of 40 ppb of O3 and 10^6 cm^-3 of OH radicals, the lifetimes span between 8 and more than 35 days and 24 and more than 54 days, respectively. This study shows that the reactivity in the particle phase is slower than in the gas phase and confirm the necessity to be taken into account. Degradation products are identified and reaction mechanism is proposed bringing to light the formation of compounds more toxic than their precursors
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Spittler, Markus. „Untersuchungen zur troposphärischen Oxidation von Limonen Produktanalysen, Aerosolbildung und Photolyse von Produkten /“. [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96450927X.
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Hussain, Altaf. „Photolysis of 2-pentyl nitrite : quantum yield and relevance to atmospheric chemistry“. Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312620.
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One of the remaining problems associated with the photo-degradation of organic species in the atmosphere, is concerned with the mechanisms of C5 and larger fragments. In this respect the 2-pentoxy radical has been chosen as a model radical. The subsequent mechanisms for it are thought to be similar to those for all other larger species. The photolysis of 2-pentyl nitrite in the near ultraviolet (UV) region at 328-383 nm resulted in the formation of 2-pentoxy radicals and nitric oxide with the quantum yield of 0.97 ± 0.08 at 298-393K, consistent with the assumption that the quantum yield was unity for alkyl nitrites. In the present work, tert-butyl nitrite has been shown to be unity. The reactions of the model radical were investigated in inert (CF4), and oxygen atmospheres, by end product analysis using on-line gas-liquid chromatography. The expected reaction routes were: decomposition, oxidation (β-H atom abstraction), and 1,5-H shift isomerisation which would produce acetaldehyde, 2-pentanone and acetone respectively. Its reaction scheme was evaluated by comparing the experimental with model results, derived by the Gear Algorithm. The estimated or calculated rate constants in the literature were "brute force" adjusted to adapt the modelling results to the experimental results. Our investigations suggested, among the rate constants for the 2-pentoxy radical: kdec 9.2 x 103s-1: CH3CH(O)(CH2)2CH3 → n-CH3CHO + n-C3H7, k02 7.0 x 105M-1s-1: CH3CH(O)(CH2)2CH3+02 → CH3C(O)(CH2)2CH3 + HO2, and kisom 1.4 x 104s-1; CH3CH(O)(CH2)2CH3 → CH3CH(OH)(CH2)2CH2) The 1,5-H shift isomerisation is relatively fast. The Arrhenius parameters of these rate constants were also modified.
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Laine, Patrick L. „Laser flash photolysis studies of halogen atom reactions of atmospheric interest“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42817.
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The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide).
The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an atmospheric degradation pathway for each alkyl bromide is qualitatively assessed.
The studies of halogen atom reactions with alkenes focused on formation of weakly-bound adducts where kinetics of adduct formation and dissociation as well as non-adduct forming channels were evaluated. The elementary steps in the Br initiated oxidation of the alkenes 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-2-butene (tetramethylethylene, TME), and 1,3-butadiene have been investigated. The experimental kinetic database for these reactions is quite sparse. The kinetic results reported herein, suggests that Br reaction with the above olefins is much faster than previously thought. Analysis of the temperature dependence of the "approach to equilibrium" kinetic data in conjunction with electronic structure calculations allows for determination of enthalpy and entropy changes associated with each addition reaction. Where possible, both forward addition and reverse dissociation channels as well as H-abstraction pathways were characterized. The enthalpy change associated with the addition reaction to give the Br−isoprene and Br−1,3-butadiene adducts has been determined for the first time and the bond dissociation enthalpy obtained for the Br−TME adduct is in reasonable agreement with the only other previously reported value. It should be noted that in the case of isoprene and 1,3-butadiene, there are multiple possible adducts that could be formed. In order to help clarify which adducts are more or less likely to be formed, we rely on electronic structure calculations (see Chapter 5) to aid in our overall understanding of the adduct forming channels. Furthermore, for the Br reactions with the three alkenes above, atomic Br kinetics have been monitored directly both in the absence and in the presence of O2 which allowed, for the first time, determination of rate coefficients for the elementary steps in the overall complex mechanism including determination of the Br−olefin + O2 rate coefficient.
Also included in this group of reactions is the chlorine reaction with isoprene. In addition to the well-known fact that isoprene is emitted into the atmosphere from vegetation, a potentially significant marine source of isoprene has received considerable attention. Chlorine has long been thought to exist primarily in marine environments, however, recent findings also suggest a significant Cl production rate in the middle of the continental United States. There are numerous room temperature kinetic studies for the Cl + isoprene reaction in the literature, however, there is only one temperature dependent study reported. Current recommended 298 K rate coefficients for isoprene reactions suggest the Cl reaction is ~ 4x faster than the analogous OH reaction. If indeed this is the case, the Cl reaction could play a non-neglibible role in isoprene oxidation in atmospheric locales where Cl concentrations are relatively high. In addition, the C−Cl bond strength in Cl−C5H8 is obtained from direct measurements of the forward and reversible addition rate coefficients. Our results are compared with the literature data, and the potential importance of Cl-initiated oxidation as an atmospheric sink for isoprene is assessed.
The final group of reactions investigated involves reactions of Cl with DMS and DMSe. DMS and DMSe are the most prevalent sulfur and selenium compounds emitted to the atmosphere from the oceans. The oxidation of DMS has been studied extensively due to the interest in the possible role of DMS oxidation in the formation of sulfate aerosols, however, DMSe oxidation processes have hardly been studied at all. And, DMSe oxidation products are likely to be less volatile than the analogous DMS species. Selenium is an essential nutrient for many plants and animals; however, there is a fine line between enough and excess selenium which can be toxic. Most studies suggest that atmospheric deposition is an important source of Se contamination, and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. Since the majority of atmospheric Se exists in the form of DMSe, determination of the kinetics and oxidation mechanisms of DMSe will go a long way towards understanding the global biogeochemical cycle of Se.
Both reversible addition and H-abstraction pathways have been characterized, and the first experimental determination of bond strength of the gas-phase DMS−Cl and DMSe−Cl adducts have been obtained.
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Gladstone, Robert Vernon. „Methods for the monitoring of peroxy radicals and measurement of NOâ†2 photolysis in the atmosphere“. Thesis, University of York, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261101.
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Cui, Xiaojuan. „Research of trace gases detection methods based on mid-infrared modern photonic instruments“. Electronic Thesis or Diss., Littoral, 2011. http://www.theses.fr/2011DUNK0519.
Annotation:
Cette thèse comprend 2 parties : -Le développement et l'application d'un laser à cascade quantique en mode continu pour la mesure de l'acide nitreux à l'état de traces -La détection de traces de gaz (HC1, CH₂O, HONO) par un système laser largement accordable dans le domaine de l'infrarouge moyen, basé sur la génération d'un rayonnement à différence de fréquences (Différence Frequency Generation - DFG) dans un cristal de niobate de lithium à polarisation périodiquement inversées. Le radical d'hydroxyde (OH) est une des espèces principales dans les cycles photochimiques qui sont responsables de la formation de l'ozone, amenant à la formation de "brouillards photochimiques". Le radical d'hydroxyde conduit également à l'oxydation des hydrocarbures dans l'atmosphère. L'acide nitreux gazeux (HONO) est une source importante du radical OH qui affecte directement la capacité oxydante de l'atmosphère et contribue indirectement à la production de polluants secondaires. La mesure précise de concentration atmosphérique de HONO exige une haute sensibilité et une bonne résolution temporelle et spatiale. Le travail principal de cette thèse a été consacré au développement d'un instrument optique basé sur un laser à cascade quantique (QCL) fonctionnant en mode continu vers 8 μm (~1255 cm ֿ ¹) pour la détection de HONO. La sensibilité et la spécificité de l'instrument ont été évaluées en utilisant un échantillon de HONO produit par la réaction chimique entre le H₂SO₄ et le NaNO₂. La concentration de HONO générée a été mesurée au moyen d'un "dénuder" associé à un analyseur conventionnel de NOx. Notez que dans la couverture spectrale du QCL, seules 5 intensités de raie d'absorption de HONO avaient été référencées. Les intensités de 19 nouvelles raies d'absorption de trans-HONO vers 8 μm ont été déterminées dans le travail actuel. Ces raies d'intensité de (0.3-9)x10-²°cm².cm ֿ ¹/molécules sont très intéressantes pour la détection spectroscopique à haute sensibilité. Parmi elles, la plus forte a été employée pour la première fois pour la mesure de traces de HONO dans l'air par la spectroscopie d'absorption directe dans une cellule à multipassage de 125 m. Combinée avec la technique de modulation de longueur d'onde, la concentration minimale détectable de HONO pourrait être inférieure à 40 pptv en 1s de temps d'intégration, convenant aux mesures de HONO atmosphérique sur le terrain. Afin d'estimer l'exactitude de mesure, les pertes de HONO sur la paroi de la cellule optique ont été expérimentalement étudiées. Nous avons observé qu'en utilisant un balayage rapide (à 2.5 kHz dans notre cas) de longueur d'onde laser, ce genre de pertes de HONO n'affectent pas l'exactitude de mesure. Finalement, l'instrument à QCL développé dans le cadre de cette thèse a été évalué en laboratoire par des mesures simultanées de HONO et de CH₄. La deuxième partie de cette thèse a été concentrée sur le développement d'une source laser infrarouge généré par la différence de fréquences (DFG) en quasi-accord de phase (QPM) dans un cristal de niobate de lithium (LiNbO₃) à polarisation périodiquement inversées (PPLN). Le rayonnement DFG était accordable en longueur d'onde de 3,2 à 3,7 μm. Le système laser à DFG développé à Anthui Institute of Optics in Fine Mechanics (AIOFM) en Chine a été utilisé pour la détection de gaz à l'état de traces de HCI et de CH₂O. Afin d'explorer la bande √₁ du trans-HONO près de 2,8 μm (~3590 cm-1) pour la détection de HONO, une nouvelle approche de la DFG fonctionnant vers 2,8 μm a été développé. Un laser à titane saphir et un laser à fibre de Yb ont été utilisés comme sources de pompe pour la génération d'un rayonnement à DFG dans un cristal de PPLN. La métrologie de fréquence du rayonnement DFG a été effectuée en utilisant des spectres d'absorption de CO₂. La mesure de HONO dans cette gamme de longueurs d'onde sera effectuée dans un prochain travailThis thesis includes two parts: Development and application of a continuous-wave quantum cascade laser (CW-QCL) based instrument for measurements and study of nitrous acid (HONO) and a broadly tunable mid-infrared laser system based on difference frequency generation (DFG) in periodically poled lithium niobate (PPLN) for trace gas ( HCl, CH2O, HONO) monitoring. The OH radical is one of the key species in photochemical cycles responsible for ozone formation, which can lead to the so-called "photochemical smog" pollution. The hydroxyl radical also drives the oxidation of hydrocarbons in the atmosphere. Gaseous nitrous acid (HONO) is a major source of the OH radical in the early morning and daytime. So HONO directly affects the oxidative capacity of the atmosphere and indirectly contributes to secondary pollutants which are products of that oxidation. High accurate and precise concentration measurement of the atmospheric HONO requires high sensitivity and stability, good temporal and spatial resolution. One part of this thesis has been firstly devoted to the design of an optical instrument based on a continuous-wave (CW) quantum cascade laser (QCL) operating at 8 μm (~1255 cm ֿ ¹) for HONO detection. The sensitivity and specificity of the instrument were evaluated and described using HONO sample generated by chemical reaction of H₂SO₄ and NaNO₂. The generated HONO concentration was quantified by means of a denuder system associated with a conventional NOX analyzer. Moreover, within the limits of the QCL frequency, only 5 absorption line intensities of HONO can be found from the reference, so we measured the relative frequencies and line intensities of the remaining absorption lines especially the one which was used to do trace gas measurement. Line strengths of 19 stronger absorption lines observed are found to be around (3-90)×10-21 cm. Direct absorption spectroscopy technique combined with a 125 m multi-pass cell was applied to develop trace gas detection of HONO. In order to improve the sensitivity, wavelength modulation technique was applied, the minimum detectable HONO concentration resulting in a noise-equivalent signal was found to be about 400 ppt in 1 second integration time and fit for field measurements. HONO losses resulted from the optical cell wall was experimentally investigated. The rate constant of HONO determined in the present work might be helpful for field measurements of HONO, especially the measurements using absorption cell. Finally，the QCL-based instrument developed in the present work has been evaluated with in-door simultaneous measurements of HONO and i i CH4. The concentration of the two species obtained in the laboratory were 116 ppb and 1.5 ppm, and the corresponding 1 σ minimum detectable concentrations (MDC) in 1-second integration time are 396 ppt and 6 ppb for HONO and CH4, respectively. The other part of this thesis is focused on highly sensitive trace gas detection employing a room-temperature, broadly tunable and narrow linewidth mid-infrared difference frequency generation laser source. The mid-infrared laser system is based on quasi-phase-matched (QPM) and DFG with a multi-grating temperature-controlled periodically poled LiNbO3 (PPLN) crystal employing two near-infrared diode lasers as pump sources. The mid-infrared coherent radiation is tunable from 3.2 μm to 3.7 μm. Detection of HCl, CH2O has been carried out. According to the absorption band (3590 cm-1) of HONO from references, another DFG laser sources employing a Ti: Sapphire laser and an Yb fiber laser as pump sources was developed, and the output frequency calibration was carried out using pure CO2 gas. HONO measurement in this wavelength range will be performed in the next work
本论文主要包括两个部分：一是基于室温连续波量子级联激光器光源，设 计并搭建了一套测量HONO 气体的系统，然后用该系统进行了HONO 气体的 探测和研究。二是利用室温操作的宽调谐差频产生中红外激光器系统进行痕量 气体(HCl, CH2O，HONO)的探测。OH 自由基是光化学循环的主要物种之一，并对臭氧的形成有重要影响，从而导致所谓的“光化学烟雾”污染。OH 自由基同时也影响着大气中烃类的氧化 能力。气态亚硝酸是清晨和白天OH 自由基的一个主要来源。因此，亚硝酸直 接影响大气的氧化能力，同时也间接推动了由于氧化过程而产生的二次污染物 的形成。大气中亚硝酸浓度的精确测量需要仪器具备高的灵敏度和稳定性，以 及好的时间和空间分辨率。本论文的主要工作之一就是设计一套以8 μm (~1255 cm-1)连续波量子级联激光器为基础对HONO 气体进行探测的装置。并利用由 H2SO4 和 NaNO2 发生化学反应而产生的HONO 气体估算和描述该装置的灵敏度和特性。产生的HONO 浓度由一个溶蚀器系统和一个NOX 分析仪来量化。在该量子级联激光器频率范围内(1254.6-1256.4 cm-1) ，只能从文献中查阅到 HONO 的5 条吸收线线强，因此测量了HONO 用于进行痕量探测的吸收线以及 其他吸收线的相对频率和线强，得到的十九条较强吸收线的线强范围大约在 (3-90)×10-21 cm。用直接吸收光谱技术结合125 m 的多次反射池对HONO 进行 了痕量探测。为了提高灵敏度，开展了波长调制技术的实验研究，得到HONO 的最低探测浓度(SNR=1) 在1 s 的积分时间内为400 ppt，适合进行外场测量。研究了由光学池壁表面而导致的HONO 的衰减效应并得到一个反应率常数，这个常数可能有助于以后HONO 的场测量，特别是用吸收池的测量。测量了实验 室空气中的HONO 和CH4，得到它们的室内浓度分别为116 ppb 和1.5 ppm, 相应的1 s 积分时间内1 σ 最小可以探测的浓度分别为396 ppt 和6 ppb。论文的另一部分工作是利用一个室温操作的，宽调谐窄线宽中红外差频产 生光源进行痕量气体的探测。该中红外差频产生系统是以准相位匹配为基础，利用两台近红外半导体激光器作为泵浦源，在PPLN 晶体中进行差频，得到的 相关中红外差频输出范围为3.2 μm 到 3.7 μm。用该系统进行了HCl 和 CH2O 气体探测，说明了该装置在工业和环境监测领域有一定的应用潜力。根据文献 得到的HONO 的另一个吸收带3590 cm-1，设计了另一套以钛宝石激光器和掺 Yb 光纤激光器作为泵浦源的差频光源系统，用CO2 气体进行了差频输出光频率 校准, 下一步的工作是进行HONO 气体测量实验。
9
Kameel, Fathima R. „Optical Properties and Chemical Composition of Secondary Organic Aerosol“. Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1240332384.
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Mazumder, Shrila. „Laser flash photolysis studies of chlorine atom reactions with fluorinated propenes and methyl amines“. Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52308.
Annotation:
The research addresses two groups of reactions: chlorine atom reactions with fluorinated propenes and methyl amines. Most of the reactions were studied over a range of temperature and pressure with the goals of (i) assessing the potential importance of the reactions in atmospheric chemistry and (ii) obtaining kinetic and thermochemical information of fundamental physical–chemical interest. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of chlorine atoms to investigate chlorine atom kinetics.
Buchteile zum Thema "Photolyse – Atmosphère":
1
Barnes, I., K. H. Becker und N. Mihalopoulos. „FTIR Product Study of the Photolysis of CH3SSCH3: Reactions of the CH3S Radical“. In Dimethylsulphide: Oceans, Atmosphere and Climate, 197–210. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-017-1261-3_21.
2
Reuder, Joachim, Tullio Gori, Ansgar Ruggaber, Lucia Kins und Ralph Dlugi. „Photolysis Frequencies of Nitrogen Dioxide and Ozone: Measurements and Model Calculations“. In Biosphere-Atmosphere Exchange of Pollutants and Trace Substances, 450–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-662-03394-4_40.
3
Calvert, Jack G., Roger Atkinson, Karl H. Becker, Richard M. Kamens, John H. Seinfeld, Timothy J. Wallington und Greg Yarwood. „Reactions Of Non-Aromatic Products Of Aromatic Compound Oxidation“. In The Mechanisms Of Atmospheric Oxidation Of Aromatic Hydrocarbons, 200–229. Oxford University PressNew York, NY, 2002. http://dx.doi.org/10.1093/oso/9780195146288.003.0006.
Annotation:
Abstract The first-generation products formed from the atmospheric reactions of aromatic compounds, discussed in sections II-D, III-D, and IV-D, can also react in the atmosphere with OH radicals, N 03 radicals, and 03, and may photolyze. The available rate coefficient data for ring-retaining products are reviewed and evaluated in sections 11-B, 111-B, and IV-Band photolysis is considered in chapter VII. The available rate coefficient data concerning the reactions of non-aromatic reaction products with OH radicals, N 03 radicals, and03 are dealt with in this chapter. VI-A. Kinetic Data for Reactions of OH Radicals, NO3 Radicals, and Ozone with Non-Aromatic Products of Aromatic Compound Oxidation The format of this section is similar to that of sections 11-B, III-B, and IV-B, and the same abbreviations (see tables 11-B-0, IV-B-0) are used in the tables below for the experimental techniques. The available kinetic data for the OH radical, N03 radical, and 03 reactions are all presented here.
4
Calvert, Jack G., John J. Orlando, William R. Stockwell und Timothy J. Wallington. „The Hydroxyl Radical and Its Role in Ozone Formation“. In The Mechanisms of Reactions Influencing Atmospheric Ozone. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190233020.003.0007.
Annotation:
Although the HO radical is present in the sunlight-irradiated troposphere at very low concentrations, only about 106 molecules cm−3, it is the most important trace component in our atmosphere. It is a highly reactive transient species and is responsible for initiating the oxidation of the majority of organic compounds in the troposphere. It initiates the chain reactions that produce ozone. All the saturated, H-atom containing molecules react with HO through abstraction of an H atom. In the case of the simplest alkane, methane, reaction (1) leads to the formation of a water molecule and an alkyl (CH3) radical: . . . HO + CH4 → H2O + CH3 (1) . . . The CH3 radical released into the oxygen-rich atmosphere quickly adds O2 to give the methyl peroxy radical in reaction (2), which in NO-containing atmospheres can react to form NO2, and an alkoxy radical, CH3O, in reaction (3). In turn, this radical reacts with O2 to give an HO2 radical and a molecule of formaldehyde in (4). An HO radical can be regenerated as the HO2 molecule oxidizes NO to NO2 in (5), and the chain of events, reactions (1) through (5), leads to ozone generation through the photolysis of the NO2 molecule in reactions (6) and (7): . . . CH3 + O2 → CH3O2 (2) . . . . . . CH3O2 + NO → CH3O + NO2 (3) . . . . . . CH3O + O2 → HO2 + CH2O (4) . . . HO2 + NO → HO + NO2 (5) . . . . . . NO2 + hν → O + NO (6) . . . . . . O + O2 (+ M) → O3 (+ M) (7) . . . Methane is the least reactive of the alkanes with HO. Urban atmospheres contain a complex mixture of the more reactive larger alkanes (RH). The number of different possible geometric isomers and stereoisomers of the alkanes that can be formed by association of C and H atoms is astounding (Calvert et al., 2008). For example, there are more than a thousand structurally different molecules of molecular formula C12H26, more than a million C20H22, more than a billion of formula C25H52, and more than a trillion possible different isomers of molecular formula C31H64.
5
Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling und Timothy Wallington. „Rate Coefficients and Mechanisms for the Atmospheric Oxidation of the Alcohols“. In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0005.
Annotation:
The presence of alcohols in the atmosphere is attributable to natural and anthropogenic sources (e.g., Graedel, 1978). They are released into the atmosphere as a result of their use as fuels (e.g., methanol, ethanol), fuel additives (e.g., ethanol), solvents (e.g., ethanol, propanol) and as starting materials or intermediates for organic synthesis in a large number of industries (e.g., isobutanol, isopentanol, hexylene glycol). Vegetation also provides a significant source of alcohols to the atmosphere (Kesselmeier and Straudt, 1999; Fall, 2003). A number of saturated and unsaturated alcohols have been identified to be biogenically emitted (e.g., methanol, ethanol, methylbutenol, linalool, Z-hex-3-en-1-ol “leaf alcohol”). High ambient concentrations of certain alcohols have been measured in some areas, up to 68 ppb for ethanol in Porto Alegre, Brazil (Grosjean et al., 1998a) and up to 3 ppb for 2-methyl-3-buten-2-ol in the Colorado mountains (Goldan et al., 1993). Amore complete description of the emission sources and ambient concentrations of alcohols is given in chapter I. Reaction with OH radicals is the dominant atmospheric loss process for the saturated alcohols while reactions with NO3, O3, and photolysis are negligible.
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„Indirect Photolysis: Reactions with Photooxidants in Natural Waters and in the Atmosphere“. In Environmental Organic Chemistry, 655–86. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2005. http://dx.doi.org/10.1002/0471649643.ch16.
7
Ramteke, Dr Shobhana, und Dr Bharat Lal Sahu. „A CRITICAL REVIEW ON THE ROLE OF HYDROGEN AS A CLEAN FUEL SOURCE“. In Futuristic Trends in Chemical Material Sciences & Nano Technology Volume 3 Book 6, 101–14. Iterative International Publishers, Selfypage Developers Pvt Ltd, 2024. http://dx.doi.org/10.58532/v3bjcs6p2ch1.
Annotation:
Due to population growth and increased human activity, the world's energy requirements have significantly increased. In the modern world, fossil fuels play a significant role in providing energy, but they also contaminate the environment by releasing greenhouse gases into the atmosphere. Hydrogen is a well-known efficient energy carrier and is found in both renewable and non-renewable sources. This review article gives a general overview of the biomass (biological and thermochemical) and water splitting (photolysis, thermolysis, and electrolysis) processes that are used to create hydrogen from renewable sources. Discussions about these methods' shortcomings are present. The study also looks at a number of important obstacles to the global development of the hydrogen economy. The paper concludes with some recommendations for further research for scientists to aid in improving the efficacy of specific production construction mechanisms and policy direction to lessen investment risks in the sector to scale up the hydrogen economy.
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Calvert, Jack G., Richard G. Derwent, John J. Orlando, Geoffrey S. Tyndall und Timothy J. Wallington. „Kinetics and Mechanisms of Reactions of Cl, O(3P), NO3, and O3 with Alkanes“. In Mechanisms of Atmospheric Oxidation of the Alkanes, 104–73. Oxford University PressNew York, NY, 2008. http://dx.doi.org/10.1093/oso/9780195365818.003.0003.
Annotation:
Abstract In this chapter, kinetic data for the reactions of alkanes with Cl-atoms, O(3P), NO3, and O3 will be presented. As was noted in chapter I-C, reaction with OH is clearly the major loss process for the alkanes under most atmospheric conditions. However, reaction with Cl, O(3P), and NO3 can play a role in certain circumstances. For example, although ambient concentrations of Cl-atoms have not been firmly established and tropospheric average concentrations are likely to be less than 103 molecule cm-3 (Rudolph et al., 1996), elevated concentrations (104 molecule cm-3 or more) may be present in the marine boundary layer (MBL) (Jobson et al., 1994; Wingenter et al., 1996; 2005), in coastal areas (Spicer et al., 1998), and/or in urban regions (Tanaka et al., 2003). Reaction of O(3P) with the alkanes may play some role in polluted areas, especially in the early morning when photolysis of NO2 [a source of O(3P)] is maximized relative to O3 photolysis (a major OH source). NO3 is most abundant at night and, in fact, is the most important night time oxidant for the alkanes, although the rate at which this night time chemistry occurs cannot compete with daytime OH-initiated oxidation rates. As will be summarized in section III-E, the occurrence of any reaction between ozone and the alkanes has not been established, and these processes can certainly be ignored for any atmospheric conditions (Atkinson and Carter, 1984). Table III-A-1 presents atmospheric lifetimes for a representative set of alkanes against various oxidation pathways (OH, Cl, O(3P), NO3) for conditions found in various regions of the lower atmosphere.
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Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling und Timothy Wallington. „Rate Coefficients and Mechanisms for the Atmospheric Oxidation of the Ketones“. In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0008.
Annotation:
Ketones are emitted directly to the atmosphere, and their sources were discussed in detail in chapter I. In the U.K. acetone and butanone comprise about 7% and 5%, respectively, of the total anthropogenic emissions of oxygenated compounds, and 1.6% and 1.1%, respectively, of the total anthropogenic emissions of nonmethane volatile organic compounds. Ketone emissions from solvents (both industrial and personal) are substantial; emissions from both gasoline- and diesel-fueled vehicles also contribute. Ketones are also formed extensively in the atmosphere in the oxidation of other compounds. Acetone, for example is formed in the OH-initiated oxidation of propane, iso-butane, iso-pentane, and neopentane and from a number of higher hydrocarbons. It is also formed in the oxidation of terpenes. The distribution, sources, and sinks of acetone in the atmosphere have been analyzed by Simpson et al. (1994). Methyl vinyl ketone is an important first generation product in the OH-initiated oxidation of isoprene. In this chapter, we discuss the rate coefficients and the mechanisms of oxidation of ketones. The classes covered include alkanones, hydroxyketones, diketones, unsaturated ketones, ketenes, cyclic ketones, ketones derived from biogenic compounds, and halogen-substituted ketones. Photolysis is a major atmospheric process for many ketones, and will be discussed in chapter IX. The major bimolecular reactions removing ketones from the atmosphere are with OH. Although less important than the OH reactions, reactions with Cl have been studied quite extensively. Other than for unsaturated ketones, reactions with NO3 and O3 are unimportant in tropospheric chemistry and have been studied little. The carbonyl group deactivates the α-position with respect to reaction with OH, but activates the β-position, and possibly more distant sites as well. The net result is that the overall rate coefficient of an alkanone generally exceeds that of the equivalent alkane. The temperature dependences of the rate coefficients can be quite complex, with acetone and possibly butanone showing a minimum in the rate coefficient at ∼250 K, while the higher alkanones show negative temperature dependences across the more limited temperature ranges that have been investigated. The most likely explanation of this behavior is the formation of a pre-reaction, hydrogen-bonded complex.
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Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling und Timothy Wallington. „Rate Coefficients and Mechanisms for the Atmospheric Oxidation of the N-Atom-Containing Oxygenates“. In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0011.
Annotation:
The many different nitrogen-containing oxygenated volatile organic compounds that are present in the troposphere play important roles in the chemistry of our atmosphere. They can be emitted directly into the atmosphere, such as in the case of amides that are widely used as organic solvents, starting materials, or intermediates in different industries (e.g., synthetic polymers, manufacture of dyes, and synthesis of pesticides). Amides are formed in situ as intermediate products in the degradation of amines (e.g., see Tuazon et al., 1994; Finlayson-Pitts and Pitts, 2000). Nitrogen-containing oxygenated organic compounds are formed in the atmosphere also via reactions of alkoxy (RO) and alkyl peroxy radicals (RO2) with NO or NO2 leading to alkyl nitrates, alkyl nitrites, and peroxy acetyl nitrates. However, primary sources of these organic species have also been suggested such as diesel and other engines and biomass burning (e.g., see Simpson et al., 2002). Alkyl nitrates (RONO2) have been detected in both the urban and the remote troposphere (e.g., see Roberts, 1990; Walega et al., 1992; Atlas et al., 1992; Ridley et al., 1997; and Stroud et al., 2001; see also section I-D). Nitrates are formed as minor products in the reaction of peroxy radicals with NO. The nitrate yield increases with the size of peroxy radicals and can be as high as 20–30% for large (>C6) radicals (Calvert et al., 2008). Peroxyacyl nitrates (RC(O)O2NO2) are important constituents of urban air pollution. They have been identified in ambient air (e.g., see Bertman and Roberts, 1991; Williams et al., 1997, 2000; Nouaime et al., 1998; Hansel and Wisthaler, 2000; also see section I-D). They are formed from photochemical reactions via RC(O)O2 + NO2. A major role of these compounds is their capacity to act as a reservoir for NOx that can be transported from polluted urban to remote regions that are poor NOx regions and where their presence can increase NOx levels (Roberts, 1990). As with other volatile organic compounds (VOCs), once released to the atmosphere, nitrogen-containing organic compounds are expected to undergo degradation primarily via reaction with hydroxyl and nitrate radicals, reaction with ozone, and photolysis. Thermal decomposition is an important loss process for the peroxyacyl nitrates.
Konferenzberichte zum Thema "Photolyse – Atmosphère":
1
Manners, James. „A fast and flexible scheme for photolysis and radiative heating of the whole atmosphere“. In RADIATION PROCESSES IN THE ATMOSPHERE AND OCEAN. AIP Publishing, 2024. http://dx.doi.org/10.1063/5.0185476.
2
Liu, Xu, und F. J. Murcray. „N2O Vertical Profiles Retrieved from Ground-based Solar Absorption Spectra Taken at McMurdo Station During Austral Spring of 1989“. In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/orsa.1995.tuc5.
Annotation:
N2O can be a tracer of atmospheric air motion due to its long life time. Ground-based FTIR solar spectra contain information on the vertical distributions of N2O due to pressure-broadening of absorption lines. We have combined the Chahine-Twomey' relaxation method with a line-by-line layer-by-layer radiative transfer code to retrieve N2O VMR profiles from ground-based solar absorption spectra. The spectra were taken at McMurdo station during the austral spring of 1989 with a 0.02 wavenumber resolution FTIR spectrometer. Since N2O is released from troposphere and is photolyzed in the stratosphere, the line shape of its absorption is mainly due Lorentz broadening. The 0.02 wavenumber resolution is high enough for us to retrieve N2O VMR profiles up to 25 kilometers. Figure 1 shows a typical observed N2O solar spectrum near 1993.15 wavenumber (solid line) and a calculated spectrum using our profile retrieval program. The best fit is obtained by iteratively adjusting N2O VMR profile according to the formulation of Chahine and Twomey. A contour plot of N2O VMR versus altitude and julian day number is shown in Figure 2. The lower tropospheric N2O VMRs have an average value around 310 ppb. Correlations of the N2O contour with that of temperature shows interesting features of tropospheric and lower stratospheric air motions. We have also compared the total N2O column amounts retrieved from this profile retrieval method and from the PC version of the non-linear least square spectral fitting algorithm (SFIT). The temporal variations of the N2O total column amounts retrieved from two methods show excellent correlation.
3
Webb, Ann R., Richard Kift und Abdulaziz Seroji. „Deriving actinic flux and photolysis rates from spectral and multiband measurements of UV irradiance“. In Third International Asia-Pacific Environmental Remote Sensing Remote Sensing of the Atmosphere, Ocean, Environment, and Space, herausgegeben von Wei Gao, Jay R. Herman, Guangyu Shi, Kazuo Shibasaki und James R. Slusser. SPIE, 2003. http://dx.doi.org/10.1117/12.466123.
4
Mack, J. A., J. M. Price und Alec M. Wodtke. „Stimulated Emission Pumping (SEP)1 Studies of Energy Transfer in Highly Vibratonally Excited Oxygen“. In High Resolution Spectroscopy. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/hrs.1993.mb5.
Annotation:
Recent results have shown that highly vibrationally excited O2 is formed in significant quantities from the ultraviolet photolyis of ground state ozone. An important question for understanding the balance of O3 in the upper atmosphere is the lifetime of these highly vibrationally excited molecules which are proposed2 to be a photolytic source of odd oxygen atoms. In this work we report the rate constants for the collisional deactivation of SEP prepared O2(v"=18-25) by O2(v"=0), at temperatures of 295 and 395 K. The experiments are analogous to the "Pump", "Dump" and "Probe" studies carried out by Yang et al on NO.3 A pulsed tunable Argon Fluoride laser is used to "PUMP" O2 from X 3 Σ u − ground electronic state to a specific rovibrational level of the B 3 Σ g − excited electronic state via the well known Schumann-Runge bands4. A Xenon-Chloride pumped tunable dye laser system then stimulates, or "DUMPS" the O2 back to a specific excited rovibrational level of the ground electronic state. A second tunable dye laser system then "PROBES" the vibrationally excited O2 population by Laser Induced Fluorescence. By varying the time delay between the DUMP and PROBE lasers, the time dependant occupation of the prepared vibrational level is monitored. The collisional quenching rate constant for a given vibrational level is then determined from the pressure dependance of the lifetime. Implications of the measured rates for atmospheric chemical reactions are discussed.