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Pushpawela, Buddhi G. "The formation and characteristics of new particles in the atmosphere." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/122854/2/__qut.edu.au_Documents_StaffHome_StaffGroupH%24_halla_Desktop_Buddhi_Pushpawela_Thesis.pdf.
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Airborne particles play a major role in climate change and human health. Drawing on the results of extensive measurements carried out in the relatively clean environment of Brisbane and the heavily polluted megacity of Beijing, this thesis has significantly furthered our knowledge of the physical mechanisms of new particle formation in the lower atmosphere. Several characteristics of new particle formation events, such as their temporal distribution, the effect of wind speed and the role of atmospheric ions on the particle formation rate, were investigated for the very first time.
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Kumar, Ravi. "Formation and properties of iodine oxide nano-particles in the atmosphere." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582110.
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The results from the laboratory experiments of iodine oxide particle (lOP) formation processes and properties are presented. The formation and growth of lOPs, originating from molecular iodine precursor, have been studied at 293 K as a function of water vapour and sulphuric and oxalic acids vapour. Under dry conditions, a linear variation in total lOP mass in particles was observed for a range of iodine concentrations. The observed hygroscopic growth factors of <1 at RH 10 - 90% on addition of H20 vapour to the particles formed under dry conditions are consistent with the particles having a fractal-like, aggregated structure. The uptake of sulphuric acid vapour onto humidified particles lead to condensational growth, with an accommodation coefficient (α) of 0.75 ± 0.05 at RH = 90% and a predicted growth rate of ~ 0.03 - 0.3 nm per hour with respect to marine boundary layer (MBl) conditions. In contrast, growth of particles exposed to oxalic acid vapour was not observed on the experimental timescales employed, indicating an upper limit for ex of 10-3• The deliquescence behaviour of crystalline HI03 and 1205 at 273 - 303 K, and the properties (e.g. water activity, density, viscosity, and efflorescence) of subsaturated and saturated iodate solutions were investigated. The deliquescence of 1205 and HI03 crystals at 293 K occurred at a relative humidity of 80.8 ± 1.0% and 85.0 ± 1.0% respectively. These values are consistent with measured water activity values for saturated 1205 and HI03 solutions at 293 K of 0.80 ± 0.01 and 0.84 ± 0.01 respectively. Optical and Raman microscope studies at low relative humidity indicate that 103- solution droplets do not exhibit efflorescence and may become ultra-viscous or glassy under atmospherically relevant conditions. In the presence of humic acid, 103- photo-chemically transforms to aqueous rand soluble iodinated humic acid and the fixing of iodine within humic structures is likely to occur at aromatic 1,2 diol groups. Transfer of 12 to the gas phase from the reduction of 103- to r, shows the oscillatory behaviour of the 'Bray-Liebhafsky' reaction and is enhanced in the presence of H202 and salinity (CI). The reduction of 103- to r shows first - order loss rate of (1.1 ± 0.1) x 10-5 s-1 which corresponds to a lifetime ~ 2 days for 103- in marine aerosol. This lifetime is consistent with the THAMOD model predictions. The predicted uptake coefficient of 03 (35 ppbv i.e. an atmospherically relevant concentration) on 100 nM I solution at 293 K was determined as (7.0 ± 0.2) x 10-7 with a resulting I2 flux of (2.9 ± 0.1) x 109 cm-2 s-1 which is ~ 5 times larger than the modelled flux at Sao Vicente (Cape Verde Island) in the tropical Atlantic Ocean. v
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Garbarienė, Inga. "Origin, chemical composition and formation of submicron aerosol particles in the atmosphere." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140520_134625-72680.
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The objective of the work was to investigate physical and chemical properties and sources of the atmospheric aerosol particles in the submicron fraction by combining different analytical techniques. The dependence of concentrations of organic and elemental carbon in different air masses was determined and the contribution of regional and local sources to the net aerosol particle pollution was estimated. Analysis of the size distribution of carbonaceous aerosol particles in background and urban areas was performed. Biogenic organic aerosol made up 15 % of the organic aerosol mass at the Preila atmospheric pollution research station, but in the North Atlantic air masses this factor was up to 50 %. Aerosol and stable isotope ratio mass spectrometry has revealed that traffic is the primary source of aerosol particles in the city, while biomass burning is the primary source at the Rūgšteliškis background station. It was determined that secondary anthropogenic organic compounds were dominating (76 %) in Vilnius, while in Rūgšteliškis secondary biogenic organic compounds made up 50 % of the total organic aerosol mass. The influence of the long-range air mass transport on the local origin aerosol particle formation and transformation has been evaluated and it has been shown that volcanic aerosol particles can significantly change the concentration, chemical composition and size distribution of local aerosol particles in the submicron range.Disertacija skirta smulkiosios aerozolio dalelių frakcijos šaltinių, fizikinių ir cheminių savybių įvertinimui kompleksiškai apjungiant įvairius tyrimo metodus. Darbe susieti elementinės ir organinės anglies koncentracijų pokyčiai su tolimąja oro masių pernaša, įvertinta regiono bei vietinių šaltinių įtaka bendrai aerozolio dalelių taršai. Aprašyti anglies turinčių aerozolio dalelių pasiskirstymai pagal dydį foninėse vietovėse ir miesto aplinkoje. Naudojant aerozolio masių spektrometrą Preilos atmosferos užterštumo tyrimų stotyje buvo identifikuotas biogeninis organinių medžiagų šaltinis, kuris vidutiniškai sudaro 15 % nuo organinių medžiagų masės, tačiau Šiaurės Atlanto oro masėje biogeninių medžiagų indėlis siekia net 50 %. Atlikus kompleksinę aerozolio ir stabiliųjų anglies izotopų masių spektrometrinę analizę buvo nustatyta, kad pirminis anglies turinčio aerozolio dalelių šaltinis mieste yra autotransportas, o Rūgšteliškio foninėje vietovėje – biomasės deginimas. Taip pat buvo nustatyta, kad Vilniuje dominavo antropogeninės antrinės organinės medžiagos (76 %), o Rūgšteliškyje vyravo biogeninės antrinės organinės medžiagos (apie 50%). Vertinant tolimosios oro masių pernašos įtaką vietinės kilmės aerozolio dalelių formavimuisi ir kaitai, buvo nustatyta, kad vulkaninės kilmės aerozolio dalelės turi įtakos submikroninės aerozolio dalelių frakcijos koncentracijai, cheminei sudėčiai ir pasiskirstymui pagal dydį.
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Saunders, Russell W. "Laboratory studies of aerosol formation in the Earth's lower and upper atmosphere." Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433795.
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Asa-Awuku, Akua Asabea. "The effect of solute dissolution kinetics on cloud droplet formation." Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11112005-141441/.
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Lee, Charles Chi-Woo. "Multiple stable oxygen isotopic studies of atmospheric sulfate : a new quantitative way to understand sulfate formation processes in the atmosphere /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9970662.
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Hennigan, Christopher James. "Properties of secondary organic aerosol in the ambient atmosphere sources, formation, and partitioning /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26598.
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Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009.Committee Chair: Weber, Rodney; Committee Co-Chair: Bergin, Michael; Committee Member: Mulholland, James; Committee Member: Nenes, Athanasios; Committee Member: Russell, Armistead. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Villa, Andres Eduardo. "Autonomous Formation Flying and Proximity Operations Using Differential Drag on the Mars Atmosphere." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1571.
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Due to mass and volume constraints on planetary missions, the development of control techniques that do not require fuel are of big interest. For those planets that have a dense enough atmosphere, aerodynamic drag can play an important role. The use of atmospheric differential drag for formation keeping was first proposed by Carolina L. Leonard in 1986, and has been proven to work in Earth atmosphere by many missions. Moreover, atmospheric drag has been used in the Mars atmosphere as aerobraking technique to decelerate landing vehicles, and to circularize the orbit of the spacecraft. Still, no literature was available related to formation flying on Mars.
To analyze the use of differential drag on the Mars atmosphere, the researcher accessed the two high resolution models available: NASA’s Mars-GRAM and ESA’s Mars Climate Database. These models allowed the simulation of conditions that a spacecraft would experience while in orbit around the planet. To explore the feasibility, the researcher first conducted a study where Mars atmosphere density was compared to Earth atmosphere, determining its applicability. Then, a simulation using MATLAB® was conducted, using a Keplerian two-body problem including the effects of Mars zonal harmonics (i.e. J2) and drag perturbations. Two 6U CubeSat were used in the simulation with deployable drag plates of different sizes, giving the possibility of having five differential drag scenarios as means of formation control.
The conclusions showed that, although with some limitations, the use of differential drag as means of autonomous formation flying and proximity operations control is feasible using proven techniques previously validated in Low Earth Orbit. Lyapunov control was selected as the control strategy, where three different methods were evaluated and compared.
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Mauk, Rachel Grant. "Tropical Cyclone Formation in Environments with Cool SST and High Wind Shear over the Northeastern Atlantic Ocean (1975-2005)." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275445016.
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Ermel, Michael [Verfasser]. "Microbial formation of nitrous acid and its exchange processes between soils and atmosphere / Michael Ermel." Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1063756464/34.
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Dong, Fangxiao. "KINETICS OF WEDGE-TEE JOINT FORMATION DURING BRAZING OF AN ALUMINUM ALLOY UNDER CONTROLLED ATMOSPHERE." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/23.
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This work involves investigation of the kinetics data of a joint formation during aluminum alloy brazing. Data was generated by several groups of experiments conducted under conditions of a controlled oxygen level of the background brazing atmosphere. Generated data are examined to identify the phases of the joint formation and the time frame of its evolution. Specifically, the triple line kinetics data are analyzed to verify whether a power law between (1) the triple line of the molten metal preceding joint formation and (2) the formation time can be established for each formation phase. In addition, both initial and residual clad thicknesses on brazing sheets are studied to check phenomenologically an impact of silicon diffusion on joint formation. Formation shapes are also inspected in order to study if a 2-D configuration of joint formation is present. The kinetics data from different sets of experiments under adverse atmosphere conditions are compared to understand the impact of oxygen level on joint formation. This study is not necessarily aimed at building a mathematical model for T-Joint formation during brazing process, but intends to understand possible influential parameters on the development of the formation.
KEYWORDS: Aluminum Brazing, Kinetics, T-Joint, Background Atmosphere, Capillary Flow.
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D'Auria, Raffaella. "A study of ionic clusters in the lower atmosphere and their role in aerosol formation." Diss., Restricted to subscribing institutions, 2005. http://proquest.umi.com/pqdweb?did=888854191&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Galloway, Katherine Elizabeth Kamens R. M. "New particle formation in a realistic daytime urban atmosphere SO2/NOx/O3/hydrocarbon air mixtures /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,1856.
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Thesis (M.S.)--University of North Carolina at Chapel Hill, 2008.Title from electronic title page (viewed Dec. 11, 2008). "... in partial fulfillment of the requirements for the degree of Master of Science in the department of Environmental Sciences and Engineering in the School of Public Health." Discipline: Environmental Sciences and Engineering; Department/School: Public Health.
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Peterson, Harold S. "NOx formation through electrical processes in the middle atmosphere and subsequent effects on ice crystals." abstract and full text PDF (UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3316372.
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Lanzafame, Grazia Maria. "Understanding organic aerosol formation processes in atmosphere using molecular markers : a combined measurements-model approach." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS519.
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L’aérosol organique (AO) constitue une large fraction des particules de l’air ambiant qui ont des impacts majeurs sur la qualité de l’air et le climat. Ses sources et processus de formation, surtout pour l’AO secondaire (AOS), sont encore méconnus induisant sa sous-estimation par les modèles de qualité de l’air. Ce travail a pour objectif d’améliorer la modélisation de l’AO en implémentant des émissions et processus de formation de marqueurs moléculaires organiques dans le modèle de chimie-transport CHIMERE. Il est basé sur la comparaison entre des sorties de modèle et de mesures réalisées en région parisienne (site périurbain du SIRTA, 25 km SO de Paris) en 2015 et sur 10 sites urbains en hiver 2014-2015. 25 marqueurs d’AOS biogénique et anthropique ont été quantifiés en phase particulaire et gazeuse et la formation de 10 a été simulée. L’évolution des concentrations en lévoglucosan (marqueur de la combustion de biomasse) a aussi été modélisée. Les résultats ont montré que les émissions de sources ou précurseurs (manquantes ou sous-estimées), les concentrations en radicaux (NO, HO2 et RO2) et le défaut de voies de formation, sont des paramètres clés pour la simulation des marqueurs d’AOS. Une faible dépendance à la T°C du partage gaz-particule a été observée alors que le partage hydrophile non idéal, souvent négligé, semble essentiel. Le lévoglucosan est bien modélisé, même si des sous-estimations existent dans certaines régions et une importante fraction gazeuse théorétique a été mise en évidence. La comparaison mesures/modèle de marqueurs moléculaires est un outil puissant pour évaluer les émissions, les processus physico-chimiques et à terme, estimer les sources d’AOOrganic aerosols (OA) account for a large fraction of ambient air particulate matter and have strong impacts on air quality and climate. As their sources and atmospheric formation processes, notably for secondary OA (SOA), are still not fully understood, their concentrations are often underestimated by air quality models. This work aimed at improving OA modelling by implementing specific organic molecular marker emissions and formation processes into the chemistry-transport model CHIMERE. It was based on the comparison of model outputs with measurements from field studies performed in the Paris region (suburban site of SIRTA, 25 km SW of Paris) over 2015 and 10 French urban locations in winter 2014-2015. 25 biogenic and anthropogenic SOA markers have been quantified in both, particulate and gas phases and the formation pathways of 10 have been developed and simulated using CHIMERE. The evolution of levoglucosan concentrations (biomass burning marker) has been also modeled. The results obtained showed that sources and precursor emissions (missing or underestimated), radical concentrations (NO, HO2 and RO2) and the lack of formation pathways, are key parameters for the simulation of SOA markers. Gas/particle partitioning seemed poorly linked to the T°C while the inclusion of hydrophilic non-ideal partitioning, usually neglected, seemed essential. Levoglucosan was well simulated, even if some underestimations existed in some regions. A significant theoretical gaseous fraction was also highlighted. The model/measurements comparison of molecular markers is a powerful tool to evaluate precursor emissions, physicochemical processes and in the end, to estimate OA sources
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Sayanagi, Kunio M. "Numerical Modeling of Atmospheric Jet Streams on Jupiter and Saturn: Their Formation and Stability." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194651.
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I studied the atmospheric jet streams of Jupiter and Saturn through numerical simulations. Jupiter and Saturn have approximately 30 and 15 jet streams, respectively, alternatively blowing eastward and westward at the cloud level. My studies are motivated by recent space probe observations of the giant planets, which are revealing vertical structures and time dependent behaviors of the atmospheric jets. Such new findings are important keys to understanding how the jets are driven and maintained. My first project tested the hypothesis that a large convective storm on Saturn observed in 1990 decelerated the equatorial jet. The equatorial jet's speed is reported to be ∼275 ms⁻¹ today, half of the speed measured by the Voyagers in 1980-81. It has been hypothesized that the large storm is responsible for causing the observed slowdown. Our result shows that the storm's effect is insufficient to cause a slowdown of the observed magnitude. The second project investigated the formation of Jovian jet streams, namely, whether Jupiter-like atmospheric jets emerge from self-organization of small initial vortices. Thunderstorms are observed on Jupiter and have been proposed to be the sources of small-scale vorticity. Our result shows that self-organization of initial small vortices leads to east-west jets under various Jupiter-like conditions. Third, I tested the stability of shallow atmospheric jets under Jovian conditions. Deep atmospheric jets have been shown to be stable on Jupiter; however, the possibility that those jets are shallow, with the point of zero-motion at perhaps ∼100-bar level, is not well explored and deserves a thorough examination.
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Luther, Robert [Verfasser]. "Numerical Modelling of Impact Crater Formation: Material Excavation and Interaction between Ejecta and Atmosphere / Robert Luther." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1193995361/34.
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Targino, Admir Créso. "Regional studies of the optical, chemical and microphysical properties of atmospheric aerosols : Radiative impacts and cloud formation." Doctoral thesis, Stockholm University, Department of Meteorology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-740.
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Atmospheric particles are ubiquitous in the Earth’s atmosphere and have potential to influence atmospheric chemistry, visibility, global climate and human health, particularly downwind from major pollution sources. The main objective of this thesis was to investigate questions pertaining to the microphysical, chemical and optical properties of aerosol particles by using in situ data collected during four experiments carried out in different regions of the Northern Hemisphere.
The first two papers of this thesis reports on airborne measurements of the aerosol optical properties performed over the North Atlantic and the Los Angeles basin. Airmasses from Europe and North Africa are usually advected in over the North Atlantic, alternating with the background marine conditions. The results showed that the aerosols are not uniformly distributed in the area and variability in the aerosol fields occurs at sub-synoptic scales. It was also observed that the single scattering coefficient varied as the polluted plumes aged, suggesting a relationship between this quantity and transport time. The measurements performed around the Los Angeles basin showed that the area’s complex topography and local meteorological circulations exert a strong control on the distribution of the aerosol in the basin. Large spatio-temporal gradients in the aerosol optical properties were observed along a transect flown from the shore towards the mountains. Profiles flown over sites located on the mountains displayed a stratified configuration with elevated aerosol layers.
Airborne data of residual particles collected in orographic wave clouds over Scandinavia were analyzed using a single particle analysis technique. Mineral dust, organic aerosols and sea salt were the main group of particles identified. Residuals composed predominantly of mineral dust were found in glaciated clouds while organic residuals were found in liquid clouds. The results suggest that organic material may inhibit freezing and have considerable influence on supercooled clouds that form through heterogeneous pathways.
The partitioning of the aerosol particles between cloud droplets and interstitial air has been addressed in terms of their microphysical properties using data obtained at a mountain-top site in Sweden during a stratocumulus event. The results showed that the scavenging efficiency varied during the cloud event, and Aitken-mode particles were also efficiently scavenged in addition to accumulation-mode particles. It is hypothesized that alterations of the aerosol chemical composition occurred during the measurement period, modifying the hygroscopic nature of the particles and decreasing their activation diameter.
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Shefer, O. V. "Innovations in the noise immune channel direction with the space craft formation." Thesis, Київський національний університет технологій та дизайну, 2017. https://er.knutd.edu.ua/handle/123456789/6699.
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Makke, Laurent. "Modélisation tridimensionnelle du rayonnement infrarouge atmosphérique utilisant l'approximation en émissivité : application à la formation du brouillard radiatif." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1061/document.
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Afin de modéliser l'absorption dans le traitement des transferts radiatifs en milieu atmosphérique, de nombreuses méthodes plus précises et plus rapides ont été développées. La modélisation de la formation du brouillard, où le rayonnement infrarouge joue un rôle très important, nécessite des méthodes numériques suffisamment précises pour calculer le taux de refroidissement. Le brouillard radatif se forme après des conditions de ciel clair, où l'absorption est le processus radiatif dominant, en raison d'un fort refroidissement nocturne. Avec l'augmentation des ressources de calcul et le développement du Calcul Haute Performance, les modèles à bandes, pour effectuer l'intégration sur la longueur des grandeurs radiométriques, sont les plus utilisés. Toutefois, le couplage entre les transferts radiatifs 3-D et la dynamique des fluides reste très coûteux en temps de calcul. Le rayonnement augmente d'environ cinquante pourcent le temps de la simulation pour la dynamique des fluides uniquement. Pour réduire le temps passé dans une itération radiative, une nouvelle paramétrization basée sur les modèles en émissivité a été développée. Cette approche nécessite seulement une résolution de l'ETR contre $N_{text{bandes}} times N_{text{gauss}}$ pour un modèle à $N_{text{bandes}}$ avec $N_{text{gauss}}$ points de quadratures sur chaque bande. Une comparaison avec des données de simulation a été effectuée et cette nouvelle paramétrisation de l'absorption infrarouge a montré sa capacité à prendre en compte les variations des concentrations gazeuses et d'eau liquide. Une étude à travers le couplage entre le modèle développé et le code de CFD Code_Saturne a été réalisée afin valider dynamiquement notre paramétrisation. Enfin une simulation exploratoire a été effectuée sur un domaine 3-D en présence de bâti idéalisé, pour capter les effets radiatifs 3-D dûs aux hétérogénéités horizontales du champ d'eau liquide et des bâtimentsThe Atmospheric Radiation field has seen the development of more accurate and faster methods to take into account absorption. Modelling fog formation, where Infrared Radiation is involved, requires accurate methods to compute cooling rates. Radiative fog appears with clear sky condition due to a significant cooling during the night where absorption is the dominant processus. Thanks to High Performance Computing, multi-spectral approaches of Radiative Transfer Equation resolution are often used. Nevertheless, the coupling of three-dimensional radiative transfer with fluid dynamics is very computationally expensive. Radiation increases the computation time by around fifty percent over the pure Computational Fluid Dynamics simulation. To reduce the time spent in radiation calculations, a new method using the broadband emissivity has been developed to compute an equivalent absorption coefficient (spectrally integrated). Only one resolution of Radiative Transfer Equation is needed against $N_{text{band}} times N_{text{gauss}}$ for an $N_{text{band}}$ model with $N_{text{gauss}}$ quadrature points on each band. A comparison with simulation data has been done and the new parameterization of Radiative properties shows the ability to handle variations of gases concentrations and liquid water. A dynamical study through the coupling between the infrared radiation model and Code_Saturne has been done to validate our parametrization. Finally the model was tested on a 3-D domain with idealized buildings to catch 3-D infrared radiative effects due to horizontally inhomogenities of the liquid water content field and buildings
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Schulz, Christiane [Verfasser]. "Secondary organic aerosol in the pristine Amazonian atmosphere: chemical properties, formation pathways, and interactions with clouds / Christiane Schulz." Mainz : Universitätsbibliothek Mainz, 2019. http://d-nb.info/1185711856/34.
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Liu, Jiumeng. "Chemical and optical properties of organic aerosols in the atmosphere over continental US: formation, partitioning, and light absorption." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50370.
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The chemical and optical properties of particulate organic compounds remain unclear, which leaves large uncertainties in the estimation of global radiative transfer balance. Gas and find particle (PM2.5) phase formic acid concentrations were measured with online instrumentation during separate one-month studies in the summer of 2010 in Los Angeles (LA), CA, and Atlanta, GA, and the gas-particle partitioning behavior was investigated and compared with that of water-soluble organic compounds (WSOC). The diurnal profiles clearly indicated that the photochemistry production serves as a strong source for the formation of organics, while the correlation between the gas and particle phase suggested that another partitioning route, the aqueous reactions, is also very important. Later, the optical properties of light-absorbing organic compounds were examined. Little is known about the optical importance of light absorbing particulate organic compounds (brown carbon), especially its extent and absorption relative to black carbon throughout the tropospheric column. Mie theory was applied to size-resolved spectrophotometric absorption measurements of methanol and water-extracts from cascade impactor substrates collected at three surface sites around Atlanta, GA, including both urban and rural. These results were applied to similar measurements of brown carbon in extracts from aircraft bulk filter samples collected over central USA. At the surface sites predicted light absorption by brown carbon relative to total absorption (brown carbon plus pure black carbon) was about 10% and 30% at 350 nm, versus 1 and 11% at 450 nm, for water and methanol extracts, respectively. The relative contribution of brown carbon was greater in the free troposphere and significantly increased with altitude. Although this approach has limitations, it demonstrates the ubiquity and significant potential contribution of brown carbon.
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Guilyardi, Eric. "Role de la physique oceanique sur la formation/consommation des masses d'eau dans un modele couple ocean-atmosphere." Toulouse 3, 1997. http://www.theses.fr/1997TOU30278.
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Le climat de notre planete resulte d'interactions complexes entre l'atmosphere, l'ocean, la cryosphere et la biosphere. L'ocean joue un role fondamental de regulation en raison de sa forte inertie thermique. Sa capacite a stocker d'enormes quantites d'energie en son sein, eloignees d'un contact direct avec l'atmosphere, en fait la composante lente du systeme climatique. L'objet de ce travail est de contribuer a mieux comprendre les mecanismes qui gouvernent cette regulation, en particulier a travers le cycle de formation/consommation de la thermocline et des masses d'eau. Celles-ci sont formees dans l'ocean superficiel par echanges air-mer et transformees au sein de l'ocean par le melange turbulent. Cet equilibre souligne le role fondamental du melange turbulent dans l'ocean (encore tres peu connu) sur les flux air-mer et donc sur notre climat. L'outil d'etude de cette these est le modele de circulation generale (mcg) couple opa/-oasis/arpege, developpe au cerfacs en collaboration etroite avec la communaute gaston. La representation du melange turbulent, processus essentiellement sous-maille, est un des points faibles de ces mcg climatiques. A l'aide de trois simulations couplees de 40 ans, plusieurs parametrisations du melange turbulent lateral sont testees dans le mcg oceanique opa : la diffusion horizontale, la diffusion isopycnale et l'ajout d'un terme mimant la perte d'energie potentielle par instabilite barocline. Le choix de realiser cette etude de sensibilite a la physique oceanique en mode couple permet de liberer l'interface air-mer. Cette approche, associee a l'analyse de la phase d'ajustement initial, permet une mise en evidence claire et rapide du comportement de chaque parametrisation. L'analyse saisonniere de la couche de melange oceanique permet d'expliquer des changements importants de temperature de surface de la mer (sst) d'une simulation a l'autre. En particulier, la diffusion isopycnale entraine un flux de chaleur positif de l'ocean interieur vers la couche de melange entrainant des augmentations de sst de plusieurs degres celsius aux moyennes latitudes. Ce flux anti-intuitif, qui semble present dans les observations hydrographiques, est du a l'existence de gradients isopycnaux de salinite. Il met ainsi en evidence le role fondamental de la salinite dans l'equilibre thermique du systeme couple. Une technique de projection des masses d'eau sur la densite permet ensuite de quantifier l'equilibre formation/consommation sur les eaux modales de l'atlantique nord. Leur non-representation dans les simulations, due a une subduction insuffisante dans les trois cas testes, pourrait etre liee a une mauvaise representation du transport lie aux tourbillons.
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Asa-Awuku, Akua Asabea. "The effect of solute dissolution kinetics on cloud droplet formation." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10456.
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This study focuses on the importance of solute dissolution kinetics for cloud droplet formation. To comprehensively account for the kinetics, a numerical model of the process was developed. Simulations of cloud droplet growth were performed for solute diffusivity, droplet growth rates, dry particle and droplet diameters relevant for ambient conditions. Simulations suggest that high ambient supersaturations and a decrease in solute diffusivity are major contributors to significant decreases in effective solute surface concentrations. The numerical simulations were incorporated into Khler theory to assess the impact of dissolution kinetics on the droplet equilibrium vapor pressure. For CCN composed of partially soluble material, a significant increase was found in the equilibrium supersaturation of CCN.
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Landera, Alexander. "Formation of Polycyclic Aromatic Hydrocarbons and Nitrogen Containing Polcyclic Aromatic Compounds in Titan's Atmosphere, the Interstellar Medium and Combustion." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/991.
Full textAbstract:
Several different mechanisms leading to the formation of (substituted) naphthalene and azanaphthalenes were examined using theoretical quantum chemical calculations. As a result, a series of novel synthetic routes to Polycyclic Aromatic Hydrocarbons (PAHs) and Nitrogen Containing Polycyclic Aromatic Compounds (N-PACs) have been proposed. On Earth, these aromatic compounds originate from incomplete combustion and are released into our environment, where they are known to be major pollutants, often with carcinogenic properties. In the atmosphere of a Saturn’s moon Titan, these PAH and N-PACs are believed to play a critical role in organic haze formation, as well as acting as chemical precursors to biologically relevant molecules. The theoretical calculations were performed by employing the ab initio G3(MP2,CC)/B3LYP/6-311G** method to effectively probe the Potential Energy Surfaces (PES) relevant to the PAH and N-PAC formation. Following the construction of the PES, Rice-Ramsperger-Kassel-Markus (RRKM) theory was used to evaluate all unimolecular rate constants as a function of collision energy under single-collision conditions. Branching ratios were then evaluated by solving phenomenological rate expressions for the various product concentrations. The most viable pathways to PAH and N-PAC formation were found to be those where the initial attack by the ethynyl (C2H) or cyano (CN) radical toward a unsaturated hydrocarbon molecule led to the formation of an intermediate which could not effectively lose a hydrogen atom. It is not until ring cyclization has occurred, that hydrogen elimination leads to a closed shell product. By quenching the possibility of the initial hydrogen atom elimination, one of the most competitive processes preventing the PAH or N-PAC formation was avoided, and the PAH or N-PAC formation was allowed to proceed. It is concluded that these considerations should be taken into account when attempting to explore any other potential routes towards aromatic compounds in cold environments, such as on Titan or in the interstellar medium.
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Burrell, Emily. "The Investigation of Secondary Particle Formation Initiated by Non-Prototypical Sources and the role of Amines in the Atmosphere." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8634.
Full textAbstract:
This dissertation is a collection of works that investigate non-prototypical sources leading to new particle formation in the atmosphere. Particles play a major role in atmospheric chemistry. For example, particles are a component of smog and are commonly found in high concentrations under conditions of atmospheric inversions. In order to reconcile the difference between measured and modeled particle concentrations new mechanisms from non-prototypical sources for particle formation need to be determined. Formation of particles has frequently been modeled using classical nucleation theory (CNT). The first step in CNT is the nucleation step where molecular clusters form. In a second step, these clusters grow into particles through coagulation or condensation. First, this research aims to improve the modeling of equilibrium constants for the formation of peroxy radical-water complexes. Failure of the harmonic approximation in the partition function for describing the low frequency vibrational modes of the complexes was explored. Instead the dissociative hydrogen bond mode using a Lennard-Jones 6-3 potential and the other low frequency vibrational modes using one- and two-fold hindered rotors was modeled. It was determined that the contribution of the two-fold hindered rotors is more important than the long-range dipole-dipole potentials and of vibration-rotation coupling. In related work, the hydroperoxy radical was investigated as a non-prototypical source of particles using high level ab initio calculations. The results indicate that the addition of an amine to the dimer increased the overall stability of complex through the increased number and strength of the hydrogen bonds. When compared to prototypical systems, sulfuric acid and methane sulfonic acid, the strength of the complex was found to be similar to the peroxy radical system. Finally, carboxylic acids, formic acid and acetic acid, were investigated as a source for new particle formation using computational and experimental techniques. Using a slow flow reactor cell particle formation was enhanced by the addition of trimethylamine. High level ab initio calculations indicate like the peroxy radicals, carboxylic acids may act as a molecular cluster in particle formation
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Clark, Jared M. "The Formation and Stability of Radical-Molecule and Radical-Radical Complexes and Their Importance in Atmospheric Processes." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2679.
Full textAbstract:
This research explores the role that radical-molecule complexes play in the chemistry of Earth's atmosphere. The formation of such complexes can have direct and pronounced effects on the reaction and product outcome of atmospheric chemical reactions. Some attention is also given to the formation of radial-radical pre-reactive complexes in the HO + ClO system. Peroxy radicals (RO2) can form stable complexes with polar compounds such as H2O, NH3, and CH3OH. For the simplest RO2 radical, HO2, complex formation (e.g., HO2-H2O, HO2-NH3, and HO2-722;CH3OH) gives rise to a significant increase in the HO2 self-reaction rate constant. Although this phenomenon has been observed since the mid-1970s, no satisfactory explanation has been put forward to explain this effect. Herein a rationale for the enhancement of the HO2 self-reaction is given based on extensive geometric, mechanistic and natural bond orbital (NBO) analyses. The apparent lack of a rate enhancement for the methyl peroxy (CH3O2) self-reaction is also presented. The combined insights gained from these two systems are then extended to predict if a water enhancement is expected for the 2-hydroxyethyl peroxy (HOCH2CH2O2) self-reaction kinetics. The computational results of this study are then compared to experimental work and conclusions are drawn towards a general procedure to predict the presence/absence of water initiated rate enhancements in RO2 systems as a whole. Original work regarding the formation of a series of organic RO2-H2O complexes is presented. This work established the effects of different functional groups on the stability of organic peroxy radicals and makes estimates of the associated atmospheric lifetimes and equilibrium constants. This work is further extended to the family of peroxy radicals that form from the atmospheric oxidation of isoprene (the most abundant non-methane biologically emitted hydrocarbon). For the first time, complexes of isoprene peroxy radicals with water are presented along with atmospheric lifetime estimates. Conclusions are made as to the effect of water on the product branching ratio of the isoprene peroxy radical + NO2. The oxidation of hexanal to form hexanal peroxy radicals is discussed within the context of the formation of hexanal peroxy water complexes.Aerosol formation is also perturbed as a result of complexation. Aerosol formation under atmospheric conditions is hypothesized to be initiated by radical-molecule complex formation. For example, in the absence of ammonia, the nucleation of H2SO4 in water vapor to form sulfuric acid aerosols is slow. However, as the concentration of NH3 rises, a marked increase in the rate of sulfuric acid aerosol formation is observed. This work explores the effects of the photolysis products of NH3 (NH2 and NH) on the rate of aerosol formation in systems involving H2SO4, HNO3, HC(O)OH, and CH3C(O)OH. With the exception of H2SO4-NH3 and HNO3-NH3 (geometries already published in the literature), minimum energy structures are presented here for the first time for each of the acid-NHx complexes. Thermochemical data and lifetime estimates are provided for each complex. Conclusions about the relevance of acid-NH2 and acid-NH in the formation of atmospheric aerosols are set forth. Finally, mechanistic insights into the reaction of the hydroxyl radical (OH) and Cl2O are obtained via analysis of the two potential energy surfaces that both involve the formation of HO-Cl2O pre-reactive complexes.
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Gérard, Violaine. "Surfactants in atmospheric aerosols and their role on cloud formation." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1216/document.
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Les nuages sont essentiels dans le cycle de l'eau et dans le budget climatique mais certains aspects de leur formation sont encore incompris. La théorie de Köhler prédit que les surfactants devraient favoriser l'activation des particules en goutte de nuage alors que les modèles actuels les considèrent comme négligeables. Au début de ce travail de thèse, quelques études commençaient à démontrer le contraire mais des preuves du rôle de ces composés dans l'atmosphère étaient encore manquantes, d'où l'objectif de ce travail de thèse. Le développement d'une méthode pour déterminer la concentration en surfactants dans les aérosols a conduit aux premières courbes de tension de surface de surfactants atmosphériques dans des aérosols PM2.5 côtiers (Suède), et à l'identification du ratio C/CMC comme paramètre clé contrôlant l'efficacité des aérosols à former des nuages. Une seconde étude a révélé des corrélations fortes entre la présence de nuages et les propriétés intrinsèques des surfactants dans des aérosols PM1 boréaux (Finlande), démontrant pour la première fois le rôle des surfactants dans la formation des gouttes de nuage à partir d'observations directes dans l'atmosphère. Les résultats prédisent un nombre de noyaux de condensation en moyenne quatre fois plus important que lorsque les effets des surfactants étaient négligés, montrant l‘importance d'inclure l'effet des surfactants dans les modèles prédictifs. Cette importance a été confirmée en laboratoire par des expériences sur des gouttes individuelles microniques par l'augmentation de leur taille en présence de surfactants. Enfin, les observations à partir des différentes études indiquent une origine biologique des surfactants dans les aérosols atmosphériquesClouds are essential components of the Earth’s hydrological system and climate but some aspects of their formation are still not completely understood. In particular, although Köhler theory predicts that surfactants should enhance cloud droplet activation, current models consider this role negligible. At the time of this PhD work, a few studies had started to demonstrate the contrary but atmospheric evidence for the role of these compounds was still missing and very little was known about their atmospheric concentrations, sources, and mechanism of action. The objective of this PhD work was to investigate these aspects. A method was developed to quantify surfactant concentrations in aerosols. Its application led to the first absolute atmospheric surfactants’ surface tension curves, in coastal PM2.5 aerosols in Sweden, and to the identification of the ratio C/CMC as the key parameter controlling the cloud-forming efficiency of aerosols. A second study revealed strong correlations between cloud occurrence and intrinsic surfactant properties in boreal PM1 aerosols in Finland, demonstrating for the first time the role of surfactants in cloud formation from direct atmospheric observations. The results predicted Cloud Condensation Nuclei numbers four times larger on average than when neglecting surfactant effects, showing the importance of including surfactant effects in cloud predictions models. The role of surfactants inferred from macroscopic measurements was confirmed by laboratory experiments on individual micron-sized droplets showing an increase of droplet growth in the presence of surfactants. Finally, observations from the different field studies indicated a biological origin for the surfactants present in atmospheric aerosols
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Allen, Christopher J. T. "Atmospheric mechanisms of central Saharan dust storm formation in boreal summer : observations from the Fennec campaign." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:896c26f3-c7a5-4c93-9e53-69b69b28d1cb.
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In boreal summer, satellite measurements show that the central Sahara is the dustiest region of the planet. However, ground-based observations of the central Sahara have been limited to its outer edges, leaving a void in observations approximately 1 million km2 in area. The Fennec Project has been the first campaign to instrument this remote but climatologically important region. This thesis uses these new observations to detect and explain the atmospheric mechanisms that make the central Sahara the summer global dust maximum. Four atmospheric mechanisms are found to cause dust storms in the central Sahara in June 2011 and June 2012. These are cold pool outflows, low-level jets (LLJs), monsoon surges and dry convective plumes. Dust may be emitted locally by these phenomena, or be advected, principally by cold pools. In both field seasons, dust emission by cold pool outflows is the most important dust mechanism, causing roughly half of the total dust loadings at the Fennec supersite of Bordj-Badji Mokhtar (BBM), the closest station to the dust maximum. The second most important mechanism is dust advection by cold pools (roughly 30% dust at BBM), followed by dust emission by monsoon surges, LLJs and finally dry convective plumes (only 2% dust at BBM). Although June 2012 was significantly more dusty than June 2011, the relative importance of the different atmospheric dust mechanisms at BBM did not change. At the automatic weather stations (AWSs) across the remote desert, cold pools and LLJs are by far the most frequently detected atmospheric dust mechanisms. LLJs are particularly common in the Atlantic Inflow in western Mauritania and in the north-easterly Harmattan in western Algeria. Cold pools are much more frequent at BBM, the station under the greatest moist monsoon influence, than at the AWSs to the north. Detection of advected dust is a particular difficulty without dedicated dust-detection instrumentation or human observers (e.g. at the AWSs). Detection of dust emission mechanisms can be very successful with only routine ground observations and satellite measurements, but quantifying the associated dust burden without dedicated dust instruments is problematic. The choice of instrumentation for dust measurement is crucial. Because cold pool outflows - the most important dust mechanism - frequently occur at night or under cloud, sun photometers miss about half of cold pool dust. Lidars have the advantage of providing height resolved dust profiles, but they suffer from attenuation in thick dust. The nephelometer proved to be the most reliable dust instrument. Although LLJs occurred on 21/28 mornings at BBM in June 2011, only five of these jets led to dust emission. Calculations of momentum exchanges through the atmospheric column show that momentum mix-down from the jet core is the cause of dust emission on these occasions, but that the LLJ has to be particularly strong (≥ 16 m s-1) to result in dust emission at the surface. Met Office Africa-LAM underestimates monsoon LLJ wind profiles and ERA-Interim reanalysis underestimates both monsoon and Harmattan LLJ wind profiles. At the surface, the Met Office Africa-LAM and GLOBAL models significantly underpredict the frequency of observed wind speeds >6 m s-1. This will cause them to significantly underestimate dust emission, as emission is a threshold process proportional to the cube of wind speed. A particularly interesting implication of the research presented here is that the central Sahara is likely much more dusty than previously thought. This is because almost all of the techniques currently used to study dust in the region are systematically biased to result in underestimates of dust burden. Cold pools are the most important dust mechanism but, since they rarely occur during the daytime or in cloud-free conditions they are often missed by sun photometers. Many will be missed by satellites that cannot retrieve below cloud and satellites that pass over the Sahara in daylight hours (e.g. the A-train). A commonly-used satellite dust detection algorithm often misses dust under moist (i.e. cold pool) conditions. Cold pools cannot be simulated by models without explicit convection, which requires very high spatial resolution. Finally, the numerical models assessed here significantly underpredict the frequency of wind speeds over the dust emission threshold. The Sahara is probably much dustier than current estimates suggest.
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Nikolaou, Athanasia [Verfasser], Nicola [Akademischer Betreuer] Tosi, Dieter [Gutachter] Breitschwerdt, Doris [Gutachter] Breuer, and Nicola [Gutachter] Tosi. "Numerical modeling of magma ocean solidification and concurrent atmosphere formation / Athanasia Nikolaou ; Gutachter: Dieter Breitschwerdt, Doris Breuer, Nicola Tosi ; Betreuer: Nicola Tosi." Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1211392317/34.
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Bonnefoy, Mickaël. "Recherche et caractérisation des propriétés physiques et chimiques des compagnons de faible masse, naines brunes et planètes géantes, à l'aide d'observations à haut contraste et à haute résolution angulaire." Grenoble, 2010. http://www.theses.fr/2010GRENY035.
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Mon travail de thèse se place dans le contexte dynamique de la détection directe des compagnons de faible masse (naines brunes, planètes extrasolaires) dans le but de caractériser leurs propriétés physiques et chimiques et de comprendre leurs mécanismes de formation et d'évolution. Cette recherche requiert l'emploi de techniques d'observations à haut contraste et à haute résolution angulaire pour résoudre l'environnement proche des étoiles et ne pas être limité par leur flux. Dans ce cadre, j'ai eu la chance de participer à des campagnes d'observations pour tenter de détecter de nouvelles sources. J'ai élaboré un ensemble d'outils de traitement et d'analyse des données pour extraire les spectres et les flux des objets dans des bandes photométriques. Enfin, j'ai utilisé ces informations pour étudier les propriétés physiques (rayon, masse, âge) et atmosphériques (composition, température effective, gravité de surface) de ces objets. La première partie de ce manuscrit se focalise sur la détection par imagerie des compagnons de faible masse jeunes (< 100 millions d'années). Je décris un ensemble d'outils de réduction et d'analyse, spécifiques à la technique d'imagerie angulaire différentielle, que j'ai mis en place. Ces outils ont été utilisés sur des données provenant de l'instrument NaCo situé au Very Large Telescope (Chili). Ils ont permis de redétecter la planète extrasolaire β Pictoris b. Ce compagnon est le plus proche de son étoile de toutes les exoplanètes détectées directement. Cette découverte fournit la preuve directe que des planètes géantes se forment en moins de 12 millions d'années à l'intérieur de disques. Je présente enfin l'analyse complémentaire que j'ai menée pour initier la caractérisation de cet objet particulier. Le second volet de mon travail, présenté dans la deuxième partie du manuscrit, est axé sur la détermination des propriétés spectroscopiques dans le proche infrarouge (1. 1-2. 5 µm) des objets de faible masse jeunes. Ce travail a débuté par l'optimisation et le développement d'outils de traitement et d'analyse des données du spectrographe intégral de champ SINFONI assisté par optique adaptative. Les efforts déployés ont permis d'analyser le spectre du compagnon naine brune/exoplanète AB Pic b. Ce travail s'est poursuivi par la construction d'une bibliothèque de spectres d'objets jeunes. Cette bibliothèque fournie un ensemble de spectres de référence pour l'étude des compagnons détectés. Elle apporte des contraintes inédites sur les dernières générations de modèles d'atmosphère froids. Enfin, j'ai tiré parti de l'expérience acquise sur les instruments NaCo et SINFONI pour caractériser le système binaire TWA 22AB qui pourrait calibrer les modèles d'évolution des objets de faible masseMy work takes place in the dynamic context of the direct detection of low mass companions (brown dwarfs, extrasolar planets). I intent to characterize their physical and chemical properties, and to understand the mechanisms that lead to their formation and drive their evolution. This requires using high contrast and high angular resolution techniques in order to resolve the close environment of the stars without being limited by their flux. I had the opportunity to participate to observational campaigns so as to detect new sources. I developed a set of data analysis tools designed to extract the spectra and the flux of the objects into photometric bands. Finally, I used this information to study the physical (radius, mass, age) and the atmospheric (composition, effective temperature, surface gravity) properties of these objects. The first part of this manuscript focus on the detection of young (age < 100 Myrs) low mass companions using imaging. I describe a set of reduction and analysis tools dedicated to the angular differential imaging technique. These tools have been used on data coming from the NaCo instrument located on the Very Large Telescope (Chile). They allowed re-detecting the extrasolar planet β Pictoris b. This companion is closer to its star than any of the extrasolar planets detected directly so far. This discovery brings the definite proof that giant planets can form in less than 12 million years within disks. I finally present a complementary analysis I conducted to initiate the characterization of this valuable object. The determination of the spectroscopic properties of young and low mass objects in the near infrared (1. 1-2. 5 µm) constitutes the second aspect of my work (and is reported in the last part of the manuscript). I started developing analysis and processing tools dedicated to data gathered on the adaptive optics assisted integral field spectrograph SINFONI. These efforts were used to analyze the spectrum of the planet/brown dwarf companion AB Pic b. This work was pursued to built a spectral library of young objects. This library brings a collection of reference spectra, necessary for the study of other young companions. It also brings new constraints on the latest generation of atmospheric models of cool objects. To conclude, I used the instrument NaCo and SINFONI to characterize the binary system TWA 22AB that could calibrate evolutionary models of low mass objects
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Mejia, Jaime F. "Long-term trends in fine particle number concentrations in the urban atmosphere of Brisbane : the relevance of traffic emissions and new particle formation." Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/26283/1/Jaime_Mejia_Thesis.pdf.
Full textAbstract:
The measurement of submicrometre (< 1.0 m) and ultrafine particles (diameter < 0.1 m) number concentration have attracted attention since the last decade because the potential health impacts associated with exposure to these particles can be more significant than those due to exposure to larger particles. At present, ultrafine particles are not regularly monitored and they are yet to be incorporated into air quality monitoring programs. As a result, very few studies have analysed their long-term and spatial variations in ultrafine particle concentration, and none have been in Australia.
To address this gap in scientific knowledge, the aim of this research was to investigate the long-term trends and seasonal variations in particle number concentrations in Brisbane, Australia. Data collected over a five-year period were analysed using weighted regression models. Monthly mean concentrations in the morning (6:00-10:00) and the afternoon (16:00-19:00) were plotted against time in months, using the monthly variance as the weights. During the five-year period, submicrometre and ultrafine particle concentrations increased in the morning by 105.7% and 81.5% respectively whereas in the afternoon there was no significant trend. The morning concentrations were associated with fresh traffic emissions and the afternoon concentrations with the background. The statistical tests applied to the seasonal models, on the other hand, indicated that there was no seasonal component.
The spatial variation in size distribution in a large urban area was investigated using particle number size distribution data collected at nine different locations during different campaigns. The size distributions were represented by the modal structures and cumulative size distributions. Particle number peaked at around 30 nm, except at an isolated site dominated by diesel trucks, where the particle number peaked at around 60 nm. It was found that ultrafine particles contributed to 82%-90% of the total particle number. At the sites dominated by petrol vehicles, nanoparticles (< 50 nm) contributed 60%-70% of the total particle number, and at the site dominated by diesel trucks they contributed 50%. Although the sampling campaigns took place during different seasons and were of varying duration these variations did not have an effect on the particle size distributions. The results suggested that the distributions were rather affected by differences in traffic composition and distance to the road.
To investigate the occurrence of nucleation events, that is, secondary particle formation from gaseous precursors, particle size distribution data collected over a 13 month period during 5 different campaigns were analysed. The study area was a complex urban environment influenced by anthropogenic and natural sources. The study introduced a new application of time series differencing for the identification of nucleation events. To evaluate the conditions favourable to nucleation, the meteorological conditions and gaseous concentrations prior to and during nucleation events were recorded. Gaseous concentrations did not exhibit a clear pattern of change in concentration. It was also found that nucleation was associated with sea breeze and long-range transport. The implications of this finding are that whilst vehicles are the most important source of ultrafine particles, sea breeze and aged gaseous emissions play a more important role in secondary particle formation in the study area.
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Mejia, Jaime F. "Long-term trends in fine particle number concentrations in the urban atmosphere of Brisbane : the relevance of traffic emissions and new particle formation." Queensland University of Technology, 2008. http://eprints.qut.edu.au/26283/.
Full textAbstract:
The measurement of submicrometre (< 1.0 m) and ultrafine particles (diameter < 0.1 m) number concentration have attracted attention since the last decade because the potential health impacts associated with exposure to these particles can be more significant than those due to exposure to larger particles. At present, ultrafine particles are not regularly monitored and they are yet to be incorporated into air quality monitoring programs. As a result, very few studies have analysed their long-term and spatial variations in ultrafine particle concentration, and none have been in Australia.
To address this gap in scientific knowledge, the aim of this research was to investigate the long-term trends and seasonal variations in particle number concentrations in Brisbane, Australia. Data collected over a five-year period were analysed using weighted regression models. Monthly mean concentrations in the morning (6:00-10:00) and the afternoon (16:00-19:00) were plotted against time in months, using the monthly variance as the weights. During the five-year period, submicrometre and ultrafine particle concentrations increased in the morning by 105.7% and 81.5% respectively whereas in the afternoon there was no significant trend. The morning concentrations were associated with fresh traffic emissions and the afternoon concentrations with the background. The statistical tests applied to the seasonal models, on the other hand, indicated that there was no seasonal component.
The spatial variation in size distribution in a large urban area was investigated using particle number size distribution data collected at nine different locations during different campaigns. The size distributions were represented by the modal structures and cumulative size distributions. Particle number peaked at around 30 nm, except at an isolated site dominated by diesel trucks, where the particle number peaked at around 60 nm. It was found that ultrafine particles contributed to 82%-90% of the total particle number. At the sites dominated by petrol vehicles, nanoparticles (< 50 nm) contributed 60%-70% of the total particle number, and at the site dominated by diesel trucks they contributed 50%. Although the sampling campaigns took place during different seasons and were of varying duration these variations did not have an effect on the particle size distributions. The results suggested that the distributions were rather affected by differences in traffic composition and distance to the road.
To investigate the occurrence of nucleation events, that is, secondary particle formation from gaseous precursors, particle size distribution data collected over a 13 month period during 5 different campaigns were analysed. The study area was a complex urban environment influenced by anthropogenic and natural sources. The study introduced a new application of time series differencing for the identification of nucleation events. To evaluate the conditions favourable to nucleation, the meteorological conditions and gaseous concentrations prior to and during nucleation events were recorded. Gaseous concentrations did not exhibit a clear pattern of change in concentration. It was also found that nucleation was associated with sea breeze and long-range transport. The implications of this finding are that whilst vehicles are the most important source of ultrafine particles, sea breeze and aged gaseous emissions play a more important role in secondary particle formation in the study area.
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Miyazaki, Koji. "Study of the nature and roles of peroxy radicals in the atmosphere towards the understanding of oxidant formation using laser-flash photolysis and LIF detection technique." Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10074/document.
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Les radicaux peroxydes RO2 (avec R = H ou CxHy) jouent un rôle important dans les cycles de photo-oxydation ayant lieu dans la troposphère. Ils sont produits principalement par l’oxydation des hydrocarbones et du monoxyde de carbone par les radicaux OH suivi de la réaction avec O2. Ils peuvent réagir avec NO pour former du NO2 qui est une source importante d’ozone troposphérique. Pour comprendre les mécanismes de génération de l’ozone troposphérique, des mesures précises et reproductibles des concentrations des radicaux peroxydes sont essentielles. A cela, des études de cinétiques, comme la mesure du temps de vie des radicaux peroxydes, sont nécessaires. Des études récentes ont montré des différences importantes entre les concentrations de radicaux peroxydes mesurées en air ambiant et celles calculées grâce aux modèles de chimie atmosphériques. Ceci peut être dû à des chemins réactionnels manquants et à l’incertitude sur les constantes de vitesses. Deux nouvelles techniques ont été développées afin d’examiner ces différences. La première technique permet la mesure sélective des radicaux HO2 et RO2 par la technique PERCA. Les radicaux HO2 sont ôtés sélectivement en utilisant un « glass denuder ». La seconde technique a pour but la mesure de la vitesse totale de disparition des radicaux HO2 dans l’atmosphère en utilisant la combinaison de la photolyse laser avec la FIL pour la détection de HO2. Les radicaux HO2 générés par photolyse laser réagissent avec les espèces réactives présentes dans l’air ambiant comme les NOx. La vitesse de disparition de HO2 est mesurée en utilisant la FIL à 308 nm après conversion chimique des HO2 grâce à l’ajout de NOPeroxy radicals RO2 (with R = H or CxHy) play an important role in the photo-oxidation cycles of the troposphere. They are produced mainly via the atmospheric oxidation of hydrocarbons and carbon monoxide by OH radicals and subsequent reactions with O2. They can further react with NO to produce NO2, witch is an important reaction of tropospheric ozone generation. To understand the mechanism of this tropospheric ozone generation, precise and accurate measurements of ambient peroxy radical concentrations are essential. And not only atmospheric concentration measurements but also atmospheric kinetics studies such as lifetime measurements of peroxy radicals are necessary. Recent publications show big differences between measured peroxy radical concentrations and those calculated with chemical models. These could be caused by missing reaction pathways and uncertainties in reaction yields and rate constants. To investigate these missing reactions and the uncertainties in known peroxy radical reactions via ambient measurements, newly developed two instruments as described below are applied. One is a technique for the selective measurement of atmospheric peroxy radical concentrations of HO2 and RO2 using the PERCA technique. HO2 radicals are selectively removed by using a glass denuder to achieve the selective measurement. The other one is a technique for total HO2 loss rate measurement in the atmosphere by using laser-flash photolysis and LIF detection of HO2. Generated HO2 radicals by laser-flash photolysis react with ambient reactive species such as NOX in the reaction tube. HO2 loss is measured using LIF at 308 nm coupled with chemical conversion with NO
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Foucart, Brice. "Observation et modélisation de la Formation de Nouvelles Particules (FNP) au sein du panache volcanique du Piton de la Fournaise." Thesis, La Réunion, 2019. http://www.theses.fr/2019LARE0014/document.
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L'activité volcanique peut représenter une source naturelle de pollution atmosphérique. Cette pollution peut engendrer une dégradation de la qualité de l'air, affecter la santé humaine et perturber la sécurité aérienne. Le Piton de la Fournaise à La Réunion est l'un des volcans basaltique les plus actifs au monde. Ses éruptions sporadiques génèrent des panaches volcaniques essentiellement constitués de gaz et de nanoparticules qui se propagent dans l'atmosphère. En journée, la formation d'oxydants (photolyse) permet d'oxyder une partie du dioxyde de soufre en acide sulfurique. Les molécules d'H2SO4 peuvent réagir avec les molécules d'eau atmosphérique pour former des embryons via la nucléation binaire homogène. Puis, ces embryons grossissent grâce aux processus de condensation et/ou coagulation conduisant alors à la formation d'un aérosol volcanique submicronique. Cette thèse vise à observer, comprendre et modéliser les processus de Formation de Nouvelles Particules (FNP) au sein des panaches volcaniques. De ce fait, elle s'organise en deux parties. La première se base sur les données recueillies lors de la campagne multidisciplinaire STRAP menée à l’observatoire du Maïdo et au Piton de la Fournaise en 2015. Elle expose les résultats issus d’une double analyse de la fréquence et de l’intensité des événements de FNP à l’observatoire. Tandis que la première analyse s’intéresse aux processus en l’absence du panache volcanique, la seconde met en exergue les spécificités de la FNP liées à sa présence au Maïdo. La seconde partie s'axe autour de la modélisation d'abord 0D puis 3D des processus de FNP au sein des panaches volcaniques via le modèle atmosphérique Méso-NHVolcanic activity can be a natural source of air pollution. This pollution can lead to a deterioration in air quality, affect human health and disrupt aviation safety. The Piton de la Fournaise in Reunion Island is one of the most active basaltic volcanoes in the world. Its sporadic eruptions generate volcanic plumes consisting mainly of gases and nanoparticles that spread in the atmosphere. During the day, a part of the sulphur dioxide can be oxidized to sulphuric acid thanks to oxidants production (photolysis). H2SO4molecules tend to react with atmospheric water molecules and form clusters via homogeneous binary nucleation. Then, these clusters grow by condensation and/or coagulation processes leading to the formation of a submicronic volcanic aerosol. This thesis aims to observe, understand and model the New Particle Formation (NPF) processes within volcanic plumes. Consequently, it is organized in two parts. The first is based on the data gathered during the multidisciplinary STRAP campaign conducted at both the Maïdo Observatory and Piton de la Fournaise volcano in 2015. It presents the results from a dual analysis of the NPF events frequency and intensity at the observatory. While the first analysis focuses on processes in the absence of the volcanic plume, the second highlights the specificities of the NPF related to the presence of the plume at Maïdo. The second part focuses on 0D then 3D NPF processes modelling within volcanic plumes via the Meso-NH atmospheric model
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Rzeplinski, Igor. "Implications de la chimie du xénon sur les contextes planétaire et nucléaire." Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS268.
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Le xénon (Xe) est le plus lourd des gaz nobles stables. Cet élément est sujet à un paradoxe géochimique concernant son abondance élémentaire et son fractionnement isotopique. Plusieurs théories ont été envisagées comme solutions. Nous explorons ici l’hypothèse de l’incorporation du Xe dans les silicates à une pression modérée. Les échantillons sont préparés à partir de poudres minérales naturelles chargées au gaz enrichi en Xe, chauffés à des températures comprises entre 800 et 1 400 °C sous une pression de 3,5 GPa. Un fractionnement isotopique significatif a été observé pour 11 échantillons avec une valeur maximale d(Xe) = 2, 30 ± 0, 19 ‰ par unité de masse atomique. Sur la base de ces résultats nous proposons un scénario comme solution au paradoxe du Xe (Rzeplinski et al., 2022). Celui-ci consiste premièrement en l’incorporation du Xe dans les cristaux se solidifiant à partir des océans magmatiques successifs dans les 100 premiers millions d’années d’existence de la Terre. Cette incorporation favorise la rétention des isotopes lourds dans les minéraux. Ensuite, à l’occasion de chaque impact de planétésimal formant un nouvel océan magmatique, une partie significative de l’atmosphère est perdue dans l’espace. Enfin, le Xe contenu dans les silicates est progressivement dégazé et supplante la signature chondritique de l’atmosphère secondaire jusqu’à atteindre la valeur observée aujourd’hui. Ce scénario peut être étendu au cas martien. En outre, nos travaux ont abouti à l’obtention de phases contenant jusqu’à 0, 318 ± 0, 016 n%Xe. Elles ont de potentielles applications dans l’industrie nucléaire. En retardant l’apparition de bulles de Xe dans le combustible, le rendement pourrait augmenterXenon (Xe) is the heaviest element among the stable noble gases series. This element undergoes a geochemical paradox involving its elemental abundance and its isotopic fractionation. Several theories has been proposed as solutions. Here we investigate the hypothesis of Xe incorporation in silicates at moderate pressure. Samples are made from natural mineral powders loaded with Xe-enriched gas, heated up to a temperature between 800 and 1,400 °C under 3.5 GPa. A significant isotopic fractionation is observed for 11 samples showing a maximum value d(Xe) = 2.30 ± 0.19 ‰ per atomic mass unit. Based on these results, we propose a scenario as the Xe paradox solution (Rzeplinski et al., 2022). It consists firstly in the incorporation of Xe in crystals solidifying from successive magma oceans within the 100 first million years of Earth existence. This incorporation favors the heaviest isotopes retention within minerals. Then, each planetesimal impact generating a new magma ocean triggers the escape of a significant part of the atmosphere, which is lost to space. Finally, Xe contained into silicates progressively degas and overprints the chondritic signature of the secondary atmosphere until reaching nowadays observed value. This scenario can be extended to Mars. In addition, our work provides us phases containing up to 0.318 ± 0.016 n%Xe. Those materials could have a potential application in nuclear industry. By delaying the appearance of Xe bubbles in the fuel, its burnup could be increased
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Champeau, François. "Paramétrisation des processus physico-chimiques de formation des nuages et étude de leurs impacts sur l'évolution de la composition chimique atmosphérique." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2007. http://tel.archives-ouvertes.fr/tel-00717866.
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Ce travail porte sur le développement d'un module microphysique de nuages liquides et glacés dans un modèle de chimie multiphase (Leriche et al., 2001). Le modèle complet a été appliqué afin d'évaluer le rôle de ces nuages sur les teneurs en polluants atmosphériques. Les nuages modulent le transport horizontal et vertical des polluants ainsi que leur lessivage via les précipitations, ils sont aussi le siège de réactions chimiques complexes. En paramétrisant la répartition des polluants entre les différentes phases du nuage via des processus comme le givrage, la croissance des cristaux par dépôt de vapeur, la fonte et la collection des hydrométéores, il est montré l'importance de la phase glace et de la morphologie des cristaux dans l'évolution chimique du nuage. Des scénarios de formation nuageuse sont définis à partir de masses d'air continentale et / ou marine, pour voir l'influence de la capacité du nuage à précipiter sur la composition chimique des hydrométéores. Des tests sur la rétention et l'enfouissement pilotant les échanges avec la phase glacée lors du givrage et de la croissance par dépôt de vapeur respectivement ont été menés pour conclure au rôle majeur joué par la glace dans le bilan des espèces traces
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Champeau, François. "Paramétrisation des processus physico-chimiques de formation des nuages et étude de leurs impacts sur l'évolution de la composition chimique atmosphérique." Phd thesis, Clermont-Ferrand 2, 2007. http://www.theses.fr/2007CLF21748.
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Ce travail porte sur le développement d'un module microphysique de nuages liquides et glacés dans un modèle de chimie multiphase (Leriche et al. , 2001). Le modèle complet a été appliqué afin d'évaluer le rôle de ces nuages sur les teneurs en polluants atmosphériques. Les nuages modulent le transport horizontal et vertical des polluants ainsi que leur lessivage via les précipitations, ils sont aussi le siège de réactions chimiques complexes. En paramétrisant la répartition des polluants entre les différentes phases du nuage via des processus comme le givrage, la croissance des cristaux par dépôt de vapeur, la fonte et la collection des hydrométéores, il est montré l'importance de la phase glace et de la morphologie des cristaux dans l'évolution chimique du nuage. Des scénarios de formation nuageuse sont définis à partir de masses d'air continentale et / ou marine, pour voir l'influence de la capacité du nuage à précipiter sur la composition chimique des hydrométéores. Des tests sur la rétention et l'enfouissement pilotant les échanges avec la phase glacée lors du givrage et de la croissance par dépôt de vapeur respectivement ont été menés pour conclure au rôle majeur joué par la glace dans le bilan des espèces traces
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Akhoudas, Camille. "Un nouveau regard sur la dynamique de l’océan Austral et ses interactions avec la cryosphère révélé par une approche isotopique." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS464.
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L’océan Austral est un acteur central de la circulation océanique mondiale et du système climatique terrestre. Malgré l’essor des observations in situ dans cette région reculée du globe depuis les années 1990 (avec notamment le début de « l’ère satellitaire » et des grands programmes internationaux d’observations tel que WOCE, CLIVAR, GO-SHIP, ou ARGO), ce vaste océan reste encore aujourd’hui largement méconnu. Il est pourtant nécessaire de parvenir à mieux observer et comprendre les mécanismes de sa dynamique océanique ainsi que sa variabilité afin de prédire au mieux l’évolution future du système climatique. Notamment, une des particularités qui rend l’océan Austral essentiel dans le système climatique est qu’il est l’un des principaux lieux de ventilation de l’océan profond, qui permet une redistribution et un stockage de chaleur, d’eau douce, de carbone, d’oxygène, et de nutriments, entre autres. Cette ventilation est en partie dirigée par une circulation verticale unique connectant la surface aux abysses océaniques, mise en mouvement par les intenses interactions et échanges de flux d’énergie et de flottabilité entre atmosphère, océan et cryosphère. Je me penche dans cette thèse sur certains aspects de la dynamique australe en m’efforçant d’apporter une vue mécanistique de la circulation grande échelle et des changements en cours. Un fil rouge méthodologique que j’emploie sur l’ensemble de cette thèse est l’utilisation d’observations des isotopes stables de l’eau, traceur passif utilisé couramment dans un grand nombre de disciplines des sciences de la terre, mais jusque récemment assez peu en océanographie physique. La mesure des isotopes de l’eau constitue un outil, qui en tant que traceurs de l’origine de l’eau, permet de mieux caractériser les différentes composantes du cycle hydrologique ainsi que son évolution. En particulier, la composition isotopique de l’eau de mer représente une empreinte importante des masses d’eau, contenant des informations sur les conditions de leur formation et leur évolution. Dans cette thèse, au-delà du travail méthodologique important sur le terrain et en laboratoire pour l’échantillonnage, l’analyse et la calibration des mesures isotopiques, j’utilise les isotopes de l’eau en combinaison avec d’autres traceurs plus conventionnels pour aborder avec un nouveau regard, les questions du rôle des interactions entre océan et calotte polaire à la circulation grande échelle, de la signature des eaux de surface dans les abysses, ou encore de l’impact des changements de régimes atmosphériques ou de fonte de la cryosphère sur l’océan de surface. Au-delà de la seule utilisation des isotopes stables de l’eau, les approches que j’ai mises en place m’ont permis de documenter la quantité de fonte et de regel d’une des plus grandes cavités glaciaires au monde, qui influence les caractéristiques des masses d’eau denses, précurseurs des eaux abyssales se formant en mer de Weddell. Mes résultats mettent également à jour la proportion que représente, in fine, ces eaux denses dans la production des eaux abyssales dans le secteur Atlantique de l’océan Austral. Je détaille les processus qui mènent à la formation des eaux abyssales et avec cette nouvelle force, je montre que des estimations passées de la production d’eaux abyssales en apparente contradiction, s’attaquaient en réalité à différents processus. Finalement, je quantifie les changements des apports en eau douce lors des trois dernières décennies sur les tendances des propriétés de surface dans le secteur Indien de l’océan Austral. Mes résultats démontrent que des changements dans le régime des précipitations expliquent les changements des caractéristiques de l’océan surface affectant la stratification avec des conséquences sur la formation des masses d’eau et la circulation de retournement de l’océan Austral à grande échelleThe Southern Ocean is a key component in global ocean circulation and the Earth's climate system. Despite the increase of in situ observations in this remote region since the 1990s (notably with the « satellite era » and major international observation programs such as WOCE, CLIVAR, GO-SHIP, or ARGO), this immense ocean remains largely unknown. However, it is essential to observe and understand the mechanisms of its dynamics as well as its variability with the aim to predict the future evolution of the climate system. In particular, one important characteristic of the Southern Ocean is that it is one of the main sites of deep ocean ventilation, which allows redistribution and sequestration of heat, freshwater, carbon, oxygen, and nutrients. This ventilation process is mainly associated with a vertical circulation connecting the ocean surface to the abyss, fueled by intense interactions and exchanges of energy and buoyancy fluxes between atmosphere, ocean and cryosphere. In this thesis, I apprehend some aspects of the Southern Ocean dynamics by providing a mechanistic view of large-scale circulation and its ongoing changes. The approach I use throughout this thesis is based on observations of stable water isotopes, a passive tracer commonly used in a large number of earth science disciplines, but until recently only sparsely used in physical oceanography. Stable water isotopes constitute a robust tool which, as a tracer of the origin of water, help to better characterize the different components of the hydrological cycle as well as its evolution. In particular, the isotopic composition of seawater represents an important imprint of water masses, containing information on the conditions of their formation and their evolution. In this thesis, beyond the important methodological work at sea and in the laboratory for the sampling, analysis and calibration of isotopic measurements, I use the stable water isotopes in combination with other more conventional tracers to apprehend, with a new perspective, the questions of the role of interactions between the Southern Ocean and the Antarctic Ice Sheet in large-scale circulation, the signature of surface waters in the abyss, or even the impact of changes in atmospheric or cryosphere regimes on the surface ocean. Beyond the only use of stable water isotopes, original approaches have allowed me to document melting and refreezing of one of the largest ice shelves in the world, which influences the characteristics of the dense waters, precursors of abyssal waters produced in the Weddell Sea. My results also reveal the proportion of these dense waters in bottom water formation in the Atlantic sector of the Southern Ocean. We detail the processes that lead to the formation of bottom waters and with this new insight, we demonstrate that past estimates of bottom water production, in apparent contradiction, were actually focusing on different processes. Finally, I propose to quantify the changes in freshwater inputs over the past three decades that influence the trends in surface properties in the Indian sector of the Southern Ocean. The results demonstrate that changes in the precipitation regime explain changes in the surface ocean characteristics impacting stratification with consequences for large-scale water mass formation and overturning circulation in the Southern Ocean
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Bresson, Emilie. "Mécanismes de formation des systèmes convectifs quasi-stationnaires en Méditerranée nord-occidentale : application au cas du 15 juin 2010 sur le Var." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00822669.
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La Méditerranée nord-occidentale est affectée par des épisodes de pluie intense, prin- cipalement durant l'automne. L'objectif de la thèse était de mieux comprendre la relation entre les caractéristiques de l'environnement météorologique de méso-échelle et la lo- calisation et l'intensité de ces systèmes fortement précipitants, en étudiant les différents mécanismes de déclenchement et d'entretien de la convection profonde. Cette relation a d'abord été étudiée au moyen de simulations idéalisées de systèmes convectifs quasi-stationnaires affectant la région Cévenole. Des expériences de sensibilité aux caractéristiques du flux marin en terme d'humidité et de vitesse ont permis d'étudier les mécanismes expliquant la localisation du système précipitant. Les résultats de cette étude idéalisée ont ensuite été confrontés au cas des inondations du Var du 15 juin 2010. Un ensemble conséquent de simulations numériques a été réalisé afin d'obtenir la meilleure simulation de l'évènement permettant l'étude des mécanismes à l'origine du système précipitant quasi-stationnaire observé sur le Var.
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Alencar, Silvia Helena Paixao. "Aspects of stellar atmospheres and star formation." Universidade Federal de Minas Gerais, 2000. http://hdl.handle.net/1843/BUBD-9GXNVV.
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We initially investigate some processes that affect the stellar atmosphere, such as the gravity-brightening and limb-darkening, and the influence of the reflection effect on them. We study the gravity-brightening exponents using the Uppsala Model Atmospheres. In non-illuminated convective atmospheres the exponent value (beta=0.32) proposed by Lucy was confirmed only for T_eff close to 6500 K. The exponent depends upon T_eff, being rather insensitive to variations of the mixing-length parameter, the stellar mass and the use of grey or non-grey atmospheres. We demonstrate the influence of the mutual illumination in a close binary on the gravity-brightening exponent. The external illumination increases the value of beta, the larger the amount of incident flux the larger the value of the exponent. This effect is caused by the ``quenching'' of convection as the external illumination heats the surface layers of the illuminated star, bringing it closer to radiative equilibrium, where beta is close to unity. We determine monochromatic, bolometric and passband-specific limb-darkening coefficients for illuminated atmospheres. Our results show that illuminated coefficients are significantly different from the non-illuminated ones. We test different methods to calculated the coefficients and showed that in the illuminated case the method proposed by Van Hamme is recommended in order to obtain coefficients that preserve the total emergent flux from the atmosphere. In the second part of this work we study Classical T Tauri stars. We discuss the many processes acting in the forming star-disk system and test the predictions of magnetospheric accretion models. We present a spectral analysis of 30 T Tauri stars observed with the Hamilton echelle spectrograph over more than a decade. We discuss the relation between different line-forming regions and search for good accretion rate indicators. We confirm several important points of the models, such as the correlation between accretion and outflow, broad emission components that are mostly central or slightly blueshifted, and only the occasional presence of redshifted absorption. We also show, however, that the broad emission components supposedly formed in the magnetospheric accretion flow only partially support the models. Unlike the predictions, they are sometimes redshifted and are mostly found to be symmetric. The published theoretical profiles do not have a strong resemblance to our observed ones. We also present the analysis of 103 spectra of the Classical T Tauri star DR Tau. The star exhibits strong emission lines that show a wide variety and variability in profile shapes. These lines show both outflow and infall signatures which change on a variety of timescales. The system shows quasiperiodic variations in line intensities and position, but a unique period that describes all of the data could not be found. The Balmer line profiles are generally strongly peaked in the red, and do not resemble published theoretical magnetospheric accretion profiles. We suggest that the system is seen nearly pole-on. This can explain the highly asymmetric Balmer lines if the line emissivity increases strongly near the star. The Ca II and He I emission line components are found to be very symmetric and that they could be produced by magnetic turbulence.Estudaram-se inicialmente processos que afetam a atmosfera estelar como o brilho por gravidade e o escurecimento de bordo e a influência do efeito reflexão nestes processos. Os expoentes de brilho por gravidade foram determinados usando o Modelo de Atmosferas de Uppsala. Para atmosferas convectivas não iluminadas o valor do expoente proposto por Lucy (_ = 0:32) foi confirmado apenas para Tef _ 6500 K. O expoente depende de Tef , sendo bastante insensível a variações do parâmetro de comprimento de mistura, à massa da estrela e ao uso de atmosferas cinzas ou não cinzas. Mostrou-se a influência da iluminação mútua de binárias próximas no expoente de brilho por gravidade. A iluminação externa aumenta o valor de _, quanto maior o flfluxo incidente maior o valor do expoente. Esse efeito é causado pela diminuição da convecção à medida que a iluminação externa aquece as camadas superficiais da estrela iluminada, levando-a em direção ao equilíbrio radiativo, onde _ é próximo da unidade. Determinaram-se coeficientes de escurecimento de bordo monocromáticos, bolométricos e de bandas fotométricas para atmosferas iluminadas. Nossos resultados mostram que os coeficientes iluminados são significativamente diferentes dos não iluminados. Foram testados diferentes métodos de cálculo dos coeficientes e mostrou-se que, no caso iluminado, o método proposto por Van Hamme é recomendado para que se obtenha coeficientes que preservam o flfluxo total emergente da atmosfera. Na segunda parte deste trabalho foram estudadas estrelas T Tauri Clássicas. Discutiram-se vários processos que atuam no sistema de estrela e disco em formação e testaram-se as previsões dos modelos de acresção magnetosférica. Realizou-se a análise espectral de 30 estrelas T Tauri observadas com o espectrógrafo echelle Hamilton durante mais de uma década. Foram discutidas as relações entre diferentes regiões de formação de linha e procuraram-se bons indicadores de taxa de acresção de massa. Foram confirmados vários pontos importantes dos modelos, como as correlações entre acresção e perda de massa, componentes largas em emissão que se encontram quase sempre centradas ou levemente desviadas para o azul, e a presença ocasional de absorção desviada para o vermelho. Entretanto, mostrou-se também que as componentes largas em emissão que se formam supostamente no fluxo de acresção magnetosférico dão apenas suporte parcial aos modelos. Diferentes das previsões, elas aparecem ás vezes desviadas para o vermelho e são quase sempre simétricas. Além disto, os perfis teóricos publicados não se parecem muito com os que observamos. Apresenta-se também a análise de 103 espectros da estrela T Tauri Clássica DR Tau. Esta estrela exibe linhas intensas em emissão que apresentam uma grande va riedade e variabilidade de perfis. Estas linhas possuem características de acresção e perda de massa que mudam em várias escalas de tempo. As intensidades e posições das linhas de emissão mostram variações quase periódicas, mas não se obteve um período único que as descrevesse. Os perfis das linhas de Balmer mostram um pico intenso desviado para o vermelho e não se parecem com os perfis dos modelos magnetosféricos teóricos. Sugere-se que o sistema é visto quase de face. Isto pode explicar a assimetria das linhas de Balmer se a emissividade das linhas aumentar fortemente perto da estrela. As componentes das linhas de Ca II e He I em emissão são bastante simétricas e podem ter origem na turbulência magnética.
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Demarcq, Hervé. "Applications de la télédétection infrarouge et visible en océanographie. Etude de la zone de dilution rhodanienne, observations des zones de production dans le Golfe du Lion, et estimation de l'éclairement solaire global en Méditerranée Occidentale." Phd thesis, Université de la Méditerranée - Aix-Marseille II, 1985. http://pastel.archives-ouvertes.fr/pastel-00955845.
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Les travaux ont été effectués sur le golfe du Lion. Ils présentent des résultats combinés de l'interprétation d'images de satellites, obtenues dans l'infrarouge thermique (capteur AVHRR) et dans le domaine visible (capteur CZCS) avec des connaissances historiques et des mesures recueillies simultanément en mer. Ils permettent, d'une part, d'estimer la forte variabilité spatio-temporelle de la zone de dilution rhodanienne, en particulier sous l'influence du vent local et du débit du fleuve, et, d'autre part, d'observer la formation hivernale d'eau profonde dans le golfe du Lion. L'évolution saisonnière des zones de production dans le golfe du Lion est suivie à l'aide d'images de la concentration relative en pigments chlorophylliens et de la température de la mer. Le traitement d'images du spectre visible du satellite METEOSAT II permet l'estimation mensuelle de l'éclairement solaire global au niveau de la mer.
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Bellefeuille, Francis. "Satellite formation maintenance using differential atmospheric drag." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107721.
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Satellite formation flying is a very promising field for future space missions as it holds many advantages over the common monolithic satellite. However, in order for the formations to be effective, a formation maintenance scheme is required to overcome perturbations arising from different sources. In this thesis the effect of atmospheric drag on a formation is examined. To do so the Schweighart and Sedwick equations, which describe the motion of a spacecraft, called deputy spacecraft, relative to another spacecraft, referred to as the chief spacecraft, placed in a circular orbit, are modified to account for atmospheric drag. The modified equations keep the effects arising from the oblateness of the Earth, known as the J2 effects, which were included in the model proposed by Schweighart and Sedwick. A similar set of equation is then developed for satellite formations placed in orbits of small eccentricity. A formation maintenance scheme which uses differential atmospheric as a means of control is then introduced. Numerical simulation results showing the evolution of formations through time with and without active control are also provided.Le vol de satellite en formation est un domaine très prometteur pour de futures missions spatial étant donnés les nombreux avantages que cette technologie détient le satellite monolitique commun. Toutefois, pour que ces formations soient efficaces, un système de maintenance de formation est nécessaire pour surmonter les perturbations provenant de multiples sources. Dans cette these, l'effet du freinage atmosphérique sur une formation est examiné. Pour ce faire, les equations de Schweighart et Sedwick, qui décrivent le mouvement d'un engin spatial, appelé meneur, relative à un autre engine, nommé suiveur, place sur une orbite circulaire, sont modifiées pour tenir compte du freinage atmosphérique. Les equations modifiées conservent les effets découlant du fait que la Terre n'est pas parfaitement sphérique, connus comme les effets J2, qui sont inclus dans le modèle proposé par Schweighart et Sedwick. Un ensemble d'équations similaire est ensuite développé pour des formations de satellites placées sur des orbites de petites eccentricités. Un système de maintenance de formation qui utilise le freinage atmosphérique comme moyen de contrôle est introduit. Des resultats de simulations numériques montrant l'évolution dans le temps de formations avec et sans contrôle sont également fournis.
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Pettibone, Alicia Stanier Charles O. "Toward a better understanding of new particle formation." [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/420.
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Stanley, Matthew. "Hail Formation in Florida." Thesis, University of South Florida, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1555565.
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ABSTRACT Hail poses a substantial threat to life and property in the state of Florida. These losses could be minimized through better understanding of the relationships between atmospheric variables that impact hail formation in Florida. Improving hail forecasting in Florida requires analyzing a number of meteorological parameters and synoptic data related to hail formation. NOAA archive data was retrieved to create a database that was used to categorize text files of hail days. The text files were entered into the National Oceanic and Atmospheric Administration Earth System Research Laboratory website to create National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis maps of atmospheric variables for Florida hail days as well as days leading to the hail event. These data were then analyzed to determine the relationship between variables that affect hail formation, in general, across different regions and seasons in Florida using Statistical Product and Service Solutions. The reasoning for the differing factors affecting hail formation between regions, seasons and hail sizes were discussed, as well as forecasting suggestions relating to region and month in Florida. The study found that the majority of all hail that occurs in Florida is during the wet season. A low Lifted Index, high Precipitable Water and lower than average Sea Level Pressure, in most cases, is present during hail days in Florida. Furthermore, results show that Vector Wind magnitude increases as hail size increases. Additionally, several atmospheric variables useful to studying hail events, such as Lifted Index, Precipitable Water, Sea Level Pressure, Vector Wind and Temperature have significant correlations with each other depending on the region and season being observed. Strong correlations between low Lifted Index, high Precipitable Water values and the occurrence of hail events are discussed, as well as the relationship between temperature anomalies at various pressure levels and the occurrence of hail events.
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Tasoglou, Antonios. "Formation and Chemical Aging of Atmospheric Carbonaceous Aerosol." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/757.
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Atmospheric aerosols can cause serious human health problems and are also affecting the energy balance of our planet contributing to climate change. Organic aerosol (OA) is the most diverse and least understood component of submicron aerosols, in part because of a wide variety of biogenic and anthropogenic sources as well as contributions from both direct emission and secondary formation in the atmosphere. Air quality models often seriously under-predict the concentration of OA in the atmosphere due mainly to our lack of understanding of the atmospheric chemical and physical processing of the emitted organic compounds. A series of experimental studies were performed to address some of the major questions regarding atmospheric OA. In the first phase of the work, the secondary organic aerosol (SOA) production during the oxidation of β-caryophyllene by ozone (O3) and hydroxyl radicals (OH) and the subsequent chemical aging of the products during reactions with OH were investigated. Experiments were conducted with ozone, hydroxyl radicals at low NOx (zero added NOx) and at high NOx (100s of ppb). The SOA mass yield at 10 μg m-3 of organic aerosol was 27% for the ozonolysis, 20% for the reaction with OH at low NOx and 38% at high NOx under dry conditions, 20oC, and ozone excess. Parameterizations of the fresh SOA yields have been developed. The average fresh SOA atomic O:C ratio varied from 0.24 to 0.34 depending on the oxidant and the NOx level, while the H:C ratio was close to 1.5 for all systems examined. An average density of 1.06±0.1 μg m-3 of the β-caryophyllene SOA was estimated. The exposure to UV-light had no effect on the β-caryophyllene SOA concentration and Aerosol Mass Spectrometer (AMS) mass spectrum. The chemical aging of the produced β-caryophyllene SOA was studied by exposing the fresh SOA to high concentrations (107 molecules cm-3) of OH for several hours. These additional reactions ii increased the SOA concentration by 15-40% and the O:C by approximately 25%. A limited number of experiments suggested that there was a significant impact of the relative humidity on the chemical aging of the SOA. The evaporation rates of β-caryophyllene SOA were quantified by using a thermodenuder allowing us to estimate the corresponding volatility distributions and effective vaporization enthalpies. In the second step the accuracy of continuous black carbon measurements of a series of commercially available instruments was assessed for biomass burning particulate matter. Black carbon-containing particles are the most strongly light absorbing aerosols in the atmosphere. They are emitted during the combustion of fossil fuels, biofuels, and biomass. Measurements of black carbon are challenging because of its semi-empirical definition based on physical properties and not chemical structure, the complex and continuously changing morphology of the corresponding particles, and the effects of other particulate components on its absorption. In this study we compare six available commercial continuous BC instruments using biomass burning aerosol. The comparison involves a Soot Particle Aerosol Mass Spectrometer (SP-AMS), a Single Particle Soot Photometer (SP2), an aethalometer, a Multiangle Absorption Photometer (MAAP), and a blue and a green photoacoustic extinctiometer (PAX). An SP-AMS collection efficiency equal to 0.35 was measured for this aerosol system. The SP-AMS was then compared to all the other commercial instruments. Two regimes of behavior were identified corresponding to high and low organic/black carbon ratio. New mass absorption cross sections (MAC) were calculated for the optical instruments for the two regimes. The new MAC values varied from 30% to 2.3 times the instrument default values depending on the instrument and the regime. This comparison of the optical instruments suggests a stronger discrepancy among the BC measurements as the organic carbon content of the BC-containing particles increases. In the next step we focused on the chemical aging of combustion emissions. Smog chamber experiments were conducted to study the changes of the physical properties and chemical composition of biomass burning particles as they evolve in the atmosphere. A Soot Particle Aerosol Mass Spectrometer (SP-AMS) and a Single Particle Soot Photometer (SP2) were used for the chemical characterization of the particles. An Aethalometer as well as a green and a blue photoacoustic extinctiometer (PAX) were used for the study of the aerosol optical properties. As the biomass burning smoke aged, exposed to UV light, ozone, or OH radicals, organic material condensed on the preexisting particles. This coating led to an increase of the absorption of the black carbon-containing particles by as much as a factor of two. The absorption enhancement of biomass burning particles due to their coating with aromatic secondary organic aerosol (SOA) was also studied. The resulting absorption enhancement was determined mainly by the changes in the SOA mass concentration and not the changes of its oxidation state. The enhancement of the absorption of the aging biomass burning particles was consistent with the predictions of a core-shell Mie theory model assuming spherical particles and non-absorbing coating. In the last phase of the work emissions from cooking activities were studied. Cooking organic aerosol (COA) is a significant fraction of the total fine aerosol in urban areas around the world. COA chemical aging experiments took place in a smog chamber in the presence of UV light or in excess of ozone. Positive matrix factorization was used to characterize the changes in the chemical composition of the COA during the chemical aging. The chemical composition of the produced aged COA was similar for both aging methods The chemical aging processes cause an increase of the organic mass and its oxidation state. The fresh COA particles have a low CCN activity but their activity increases significantly as they chemically age.
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Bizinos, Nicholas. "Passenger comfort during formation flight within atmospheric turbulence." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/12050.
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Includes abstract.Includes bibliographical references.
Formation flight is currently being investigated as a means to reduce drag and improve fuel efficiency in commercial aviation. In light of this, the potential for passenger discomfort due to the formation flying through free air turbulence was considered in this study. In an attempt to approximately ascertain the increase in discomfort, a simple formation flight aerodynamic model for two aircraft in formation was developed. The wing trailing vortices were assumed to shift in an ideal fashion within atmospheric turbulence resulting in aerodynamic disturbance loads acting on the trailing aircraft. As the sensitivity of the human body to vibrations is frequency dependent, spectral representation of atmospheric turbulence was incorporated. Monte Carlo simulations were done for various levels of turbulence intensity.
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Wang, Shih-chen Flagan Richard C. "Aerosol formation and growth in atmospheric organic/NOx systems /." Diss., Pasadena, Calif. : California Institute of Technology, 1991. http://resolver.caltech.edu/CaltechETD:etd-01112007-152148.
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Kennedy, Michael Brian. "Understanding the formation of extreme ultraviolet radiation in solar flare atmospheres." Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.706994.
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The aim of this thesis has been to gain a better understanding of how the structure of, and physical conditions in, the lower solar atmosphere change as a result of intense energy input during solar flares. This has been achieved by employing high time resolution, broadband spectroscopic observations from the SDO/EVE instrument, in conjunction with numerical modelling of solar flares using a 1D non-LTE radiation hydrodynamics code (RADYN). The entire EUV spectrum of a sample of thirteen solar flares was characterised in terms of continuum colour temperatures, line ratios, and line to continuum ratios. It was found that the observed flare spectra were remarkably homogeneous, with little variation in the measured ratio values between different events. The Lyman continuum was found to have colour temperatures in the range 8 - 13 kK, and the continuum flux was strongly correlated with the colour temperature. The low colour temperature of the He I continuum (11 - 17 kK) suggested that it was formed through the photoionisation/recombination process in solar flares. The observed ratios of the higher Lyman lines were found to be invariant throughout each studied flare, and had values that were close to those that were calculated in the optically thin, LTE regime. These observations were compared to a grid of model atmospheres generated using the RADYN code. By examining the physical conditions in the model atmospheres it was determined that the increased electron density in the lower atmosphere of solar flares drives the hydrogen level populations closer to their LTE values. This offered an explanation for the observed temporal behaviour of the Ly a/p line ratio, and the observed ratios of the other Lyman lines. However, the simulations failed to reproduce the observed spectral energy distribution in extreme ultraviolet lines and continua.
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Thériault, Julie M. 1980 Apr 29. "Numerical studies on winter precipitation type formation." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82439.
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Winter storms produce major problems for society and their varying types of precipitation are often the key factor responsible. The objective of this study is to better understand the formation of winter precipitation types (freezing rain, ice pellets, snow, slush, wet snow and refrozen wet snow) within the varying, and interacting, environmental conditions experienced within many winter storms. A one dimensional cloud model utilizing a double-moment microphysics scheme has been developed to address this issue. Temperature and moisture profiles favorable for the formation of different winter precipitation types were varied in a systematic manner in an environment in which snow is falling continuously from above a temperature inversion. The ensuing precipitation evolved due to atmospheric temperature and moisture variations arising from phase changes such as melting and freezing. Average soundings associated with various surface precipitation types were consequently defined as well as the atmospheric conditions leading to the longest duration of various precipitation events. In addition, the reduction of visibility by precipitation was calculated to determine the conditions leading to the greatest reduction and those leading to its most rapid changes.