Letteratura scientifica selezionata sul tema "Atmospheric lifetime"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Consulta la lista di attuali articoli, libri, tesi, atti di convegni e altre fonti scientifiche attinenti al tema "Atmospheric lifetime".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Articoli di riviste sul tema "Atmospheric lifetime"
1
Sonnemann, G. R., e M. Grygalashvyly. "Effective CO<sub>2</sub> lifetime and future CO<sub>2</sub> levels based on fit function". Annales Geophysicae 31, n. 9 (27 settembre 2013): 1591–96. http://dx.doi.org/10.5194/angeo-31-1591-2013.
Testo completoAbstract (sommario):
Abstract. The estimated global CO2 emission rates and the measured atmospheric CO2 concentrations show that only a certain share of the emitted CO2 accumulates in the atmosphere. For given atmospheric emissions of CO2, the effective lifetime determines its accumulation in the atmosphere and, consequently, its impact on the future global warming. We found that on average the inferred effective lifetime of CO2 decreases as its atmospheric concentration increases, reducing the rate of its accumulation in the atmosphere. We derived a power function that fits the varying lifetimes. Based on this fitting function, we calculated the increase of CO2 for different scenarios of future global emission rates.
2
Roelofs, G. J. "A steady-state analysis of the temperature responses of water vapor and aerosol lifetimes". Atmospheric Chemistry and Physics 13, n. 16 (21 agosto 2013): 8245–54. http://dx.doi.org/10.5194/acp-13-8245-2013.
Testo completoAbstract (sommario):
Abstract. The dominant removal mechanism of soluble aerosol is wet deposition. The atmospheric lifetime of aerosol, relevant for aerosol radiative forcing, is therefore coupled to the atmospheric cycling time of water vapor. This study investigates the coupling between water vapor and aerosol lifetimes in a well-mixed atmosphere. Based on a steady-state study by Pruppacher and Jaenicke (1995) we describe the coupling in terms of the processing efficiency of air by clouds and the efficiencies of water vapor condensation, of aerosol activation, and of the transfer from cloud water to precipitation. We extend this to expressions for the temperature responses of the water vapor and aerosol lifetimes. Previous climate model results (Held and Soden, 2006) suggest a water vapor lifetime temperature response of +5.3 ± 2.0% K−1. This can be used as a first guess for the aerosol lifetime temperature response, but temperature sensitivities of the aerosol lifetime simulated in recent aerosol–climate model studies extend beyond this range and include negative values. This indicates that other influences probably have a larger impact on the computed aerosol lifetime than its temperature response, more specifically changes in the spatial distributions of aerosol (precursor) emissions and precipitation patterns, and changes in the activation efficiency of aerosol. These are not quantitatively evaluated in this study but we present suggestions for model experiments that may help to understand and quantify the different factors that determine the aerosol atmospheric lifetime.
3
Takahashi, K., T. Nakayama, Y. Matsumi, S. Solomon, T. Gejo, E. Shigemasa e T. J. Wallington. "Atmospheric lifetime of SF5CF3". Geophysical Research Letters 29, n. 15 (agosto 2002): 7–1. http://dx.doi.org/10.1029/2002gl015356.
Testo completo
4
Hoffmann, L., C. M. Hoppe, R. Müller, G. S. Dutton, J. C. Gille, S. Griessbach, A. Jones et al. "Stratospheric lifetime ratio of CFC-11 and CFC-12 from satellite and model climatologies". Atmospheric Chemistry and Physics 14, n. 22 (27 novembre 2014): 12479–97. http://dx.doi.org/10.5194/acp-14-12479-2014.
Testo completoAbstract (sommario):
Abstract. Chlorofluorocarbons (CFCs) play a key role in stratospheric ozone loss and are strong infrared absorbers that contribute to global warming. The stratospheric lifetimes of CFCs are a measure of their stratospheric loss rates that are needed to determine global warming and ozone depletion potentials. We applied the tracer–tracer correlation approach to zonal mean climatologies from satellite measurements and model data to assess the lifetimes of CFCl3 (CFC-11) and CF2Cl2 (CFC-12). We present estimates of the CFC-11/CFC-12 lifetime ratio and the absolute lifetime of CFC-12, based on a reference lifetime of 52 years for CFC-11. We analyzed climatologies from three satellite missions, the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS), the HIgh Resolution Dynamics Limb Sounder (HIRDLS), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). We found a CFC-11/CFC-12 lifetime ratio of 0.47±0.08 and a CFC-12 lifetime of 112(96–133) years for ACE-FTS, a ratio of 0.46±0.07 and a lifetime of 113(97–134) years for HIRDLS, and a ratio of 0.46±0.08 and a lifetime of 114(98–136) years for MIPAS. The error-weighted, combined CFC-11/CFC-12 lifetime ratio is 0.46±0.04 and the CFC-12 lifetime estimate is 113(103–124) years. These results agree with the recent Stratosphere-troposphere Processes And their Role in Climate (SPARC) reassessment, which recommends lifetimes of 52(43–67) years and 102(88–122) years, respectively. Having smaller uncertainties than the results from other recent studies, our estimates can help to better constrain CFC-11 and CFC-12 lifetime recommendations in future scientific studies and assessments. Furthermore, the satellite observations were used to validate first simulation results from a new coupled model system, which integrates a Lagrangian chemistry transport model into a climate model. For the coupled model we found a CFC-11/CFC-12 lifetime ratio of 0.48±0.07 and a CFC-12 lifetime of 110(95–129) years, based on a 10-year perpetual run. Closely reproducing the satellite observations, the new model system will likely become a useful tool to assess the impact of advective transport, mixing, and photochemistry as well as climatological variability on the stratospheric lifetimes of long-lived tracers.
5
Sodemann, Harald. "Beyond Turnover Time: Constraining the Lifetime Distribution of Water Vapor from Simple and Complex Approaches". Journal of the Atmospheric Sciences 77, n. 2 (10 gennaio 2020): 413–33. http://dx.doi.org/10.1175/jas-d-18-0336.1.
Testo completoAbstract (sommario):
Abstract The time water vapor spends in the atmosphere from evaporation to precipitation, termed here the water vapor lifetime, is of fundamental relevance for characterizing the water cycle, for the turnover of mass and energy, causes of precipitation extremes, and the recycling of precipitation over land. While the global average lifetime of water vapor is commonly considered as about 8–10 days, recent work indicates that the distribution of water vapor lifetimes is highly skewed, and that a large part of the water vapor could have average lifetimes of about 4–5 days. Besides calling for scrutiny of these new estimates, these findings also prompt an investigation of the factors shaping the distribution of the lifetime of water vapor. Using idealized setups and reanalysis data, I explore the influence of heterogeneity and nonstationarity on water vapor age and lifetime. The combination of nonstationarity and heterogeneity allows for short and long local lifetimes and water vapor ages, while maintaining the global average mass balance and corresponding mean water vapor lifetime. A plausibility argument based on humidity-weighted winds suggests that median lifetimes of 4–5 days are more consistent with weather system patterns in the extratropics. I propose that the median of the lifetime is more representative, since its mean value is affected by uncertainty originating from a long, thin tail. To more comprehensively understand the water vapor lifetime, methods will need to report the full lifetime distribution. Simulations with artificial water tracers could thereby provide the framework to compare different methods consistently in the future, while stable water isotopes could serve as an observational constraint.
6
Patten, K. O., e D. J. Wuebbles. "Atmospheric lifetimes and ozone depletion potentials of trans-1-chloro-3,3,3-trifluoropropylene and trans-1,2-dichloroethylene in a three-dimensional model". Atmospheric Chemistry and Physics Discussions 10, n. 7 (2 luglio 2010): 16637–57. http://dx.doi.org/10.5194/acpd-10-16637-2010.
Testo completoAbstract (sommario):
Abstract. The chloroalkenes trans-1-chloro-3,3,3-trifluoropropylene (tCFP) and trans-1,2-dichloroethylene (tDCE) have been proposed as candidate replacements for other compounds in current use that cause concerns regarding potential environmental effects including destruction of stratospheric ozone. Because tCFP and tDCE contain chlorine atoms, the effects of these short-lived compounds on stratospheric ozone must be established. In this study, we derive the atmospheric lifetimes and Ozone Depletion Potentials (ODPs) for tCFP and for tDCE assuming emissions from land surfaces at latitudes 30° N to 60° N using the MOZART 3 three-dimensional model of atmospheric chemistry and physics. Both tCFP and tDCE are shown to primarily affect ozone in the troposphere, rather than in the stratosphere as generally expected from longer-lived chlorocarbons. The atmospheric lifetime of tCFP against chemical reaction is 40.4 days, and its ODP is quite small at 0.00034. The tDCE atmospheric lifetime is 12.7 days, and its ODP is 0.00024, which is the lowest ODP found for any chlorocarbon we have studied. Our study suggests that chlorine from tCFP and tDCE are unlikely to significantly affect ozone at quantities likely to be emitted to the atmosphere.
7
Roelofs, G. J. "Aerosol lifetime and climate change". Atmospheric Chemistry and Physics Discussions 12, n. 7 (4 luglio 2012): 16493–514. http://dx.doi.org/10.5194/acpd-12-16493-2012.
Testo completoAbstract (sommario):
Abstract. The dominant removal mechanism for atmospheric aerosol is activation of particles to cloud droplets and subsequent wet deposition in precipitation. The atmospheric lifetime of aerosol is thus closely coupled to the atmospheric cycling time of water vapor. Changes of hydrological cycle characteristics resulting from climate change therefore directly affect aerosol lifetime, and thus the radiative forcing exerted by aerosol. This study expresses the coupling between water vapor and aerosol lifetimes and their temperature sensitivities in fundamental equations and in terms of the efficiency of processing of air by precipitating clouds. Based on climate model simulations these temperature sensitivities are estimated to be on the order of +5.3% K−1, but this may be an overestimation. Generally, shifting spatial and temporal patterns of aerosol (precursor) emissions and precipitation, and changes in aerosol activation efficiency probably influence aerosol lifetimes more than climate change itself, resulting in a wide range of simulated aerosol lifetime sensitivities between aerosol-climate models. It is possible that the climate sensitivity of models plays a role. It can be argued that climate sensitivity is intrinsically coupled with the simulated (temperature sensitivity of the) aerosol lifetime through the distribution of water vapor and aerosol between the lower and upper troposphere. This implies a fundamental relation between various feedback forcings (water vapor, lapse rate, cloud) and the aerosol forcing, illustrating the key role of the hydrological cycle in different aspects of the climate system.
8
Kepros, John G., e Greg Davidson. "Atmospheric Heating and Hubble's Lifetime". Physics Today 47, n. 1 (gennaio 1994): 68–69. http://dx.doi.org/10.1063/1.2808393.
Testo completo
9
Ellis, D. A., J. W. Martin, S. A. Mabury, M. D. Hurley, M. P. Sulbaek Andersen e T. J. Wallington. "Atmospheric Lifetime of Fluorotelomer Alcohols". Environmental Science & Technology 37, n. 17 (settembre 2003): 3816–20. http://dx.doi.org/10.1021/es034136j.
Testo completo
10
Fischer, Gaston. "Atmospheric lifetime of carbon dioxide". Population and Environment 10, n. 3 (marzo 1989): 177–81. http://dx.doi.org/10.1007/bf01257903.
Testo completoTesi sul tema "Atmospheric lifetime"
1
Kennett, Elizabeth Jane. "Lifetime and variability of atmospheric water vapour". Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425367.
Testo completo
2
Min, Flora. "Influence of recent Asian SO₂ and Asian NOx̳ emissions change (2001 to 2010) on particulate matter : shifts in Asian sulfate enhancement over US surface, major production pathway, and lifetime". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95565.
Testo completoAbstract (sommario):
Thesis: S.M. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.In title on title-page. double-underscored "x" appears as subscript. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 42-49).
A 3-D chemical transport model with coupled oxidant-aerosol chemistry (GEOSChem) is used to analyze the influence of recent (2001 to 2010) growth in Asian NOx and Asian SO 2 emission on transpacific transport of Asian particulate matter, especially sulfate, by quantifying and analyzing the details of chemistry and its sequential influence on transpacific transport during spring and summer. From 2001 to 2010, the spring averaged Asian sulfate enhancement in the western US model surface layer increases by 0.01-0.03 [mu]g M-3 (about 4% of the surface sulfate concentration over the US at 2010 emission level). The net chemical production rate increases in the troposphere over Asia but decreases over the Pacific Ocean. The sulfate production pathway shifts toward gas phase production by OH (7-8% increase-China; 2-3% increase-Upper atmosphere Pacific Ocean) with corresponding reductions in aqueous phase production by H202 ; resulting in a switch of the most important production pathway from aqueous production by H202 to gas phase production by OH. Almost doubling the Asian NO. emission during the period has a negligible influence on Asian sulfate enhancement over the US; this change in Asian NOx emission causes the net chemical production rate to increase in the Asian boundary layer, but to decrease in the upper Asian atmosphere, and in the atmosphere over the Pacific Ocean and the US. This is because the Asian NOx emission growth strengthens the oxidizing power in the Asian boundary layer to more actively form sulfate (mostly removed by wet scavenging), reducing available SO2 for further production away from the source. The Asian NOx emission growth is the major driver in changing the sulfate production pathways toward the gas phase. The 20% increase in Asian SO 2 emission during the period is the primary driver in increasing Asian sulfate enhancement over the US; this change accelerates net sulfate production rate, and makes a minor contribution to shifting toward gas phase production by OH over the course of the transpacific transport. The calculated sulfate column burden shows a notable increase as a response to the changes in Asian emissions. However, the shifts in sulfate lifetime over China due to changes in Asian SO 2 and/or Asian NO, emission are almost negligible (generally 1-2%), and lifetimes over the upper level Pacific Ocean are generally reduced by 3-4%.
by Flora Min.
S.M. in Atmospheric Science
3
Granneman, Jennifer E. "Evaluation of trace-metal and isotopic records as techniques for tracking lifetime movement patterns in fishes". Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7675.
Testo completoAbstract (sommario):
The focus of this work was on the use of otolith microchemistry and fish eye lens chemical profiles to measure fish movement and provided indirect support for the use of otolith microchemistry to examine exposure to crude oil. Chapter 1 provides an introduction to the applications of otolith microchemistry and eye lens isotopic profiles. In the second chapter, which examined associations between metal exposure and lesion formation in fishes collected after the Deepwater Horizon (DWH) oil spill, I did not observe any change in oil-associated metal concentrations in otoliths coinciding with the timing of the DWH oil spill. This suggests that either the technique used is not sensitive enough to detect any transient changes that may have occurred because of exposure to the oil spill or that the fish examined were not exposed to the oil spill. However, I did find that lesioned fish may have been exposed to a persistent source of trace-metals in the GoM prior to, during, and after the oil spill, and metal-induced immunomodulation may have occurred in these fish. These interactions between the physiological and environmental modulation of otolith element incorporation were explored further in Chapter 3 in which multiple tests demonstrated that physiology explained more of the variation in otolith chemical tags than ambient water chemistry. These findings suggest that the use of otolith microchemistry alone to track fish movement and potential exposure to harmful metals may be complicated by physiological control of otolith microchemistry. Thus, in Chapter 4, I pursued a novel method to evaluate the movement of fish across isoscapes of varying δ15N. I validated the use of fish eye lenses as potential lifetime recorders of isotopic histories and in Chapter 5 compared the use of fish eye lens δ15N profiles to otolith microchemistry profiles to examine fish movement. Both techniques suggested similar patterns of movement in Red Snapper from the northern GoM to the West Florida Shelf. This is the first study to use these complimentary techniques to track fish movement.
4
Zogka, Antonia. "Atmospheric degradation of a series of methoxy and ethoxy acetates and n-pentyl acetate". Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2071/document.
Testo completoAbstract (sommario):
Dans le cadre du projet DISPATMO (étude de prévision des risques de pollution liés à la dispersion atmosphérique de produits chimiques), des études de risques liés aux incendies et explosions dus aux produits chimiques ont été menées. L’objectif de cette thèse était de réaliser une étude cinétique et mécanistique approfondie afin de déterminer la dégradation en phase gazeuse de l'un des principaux constituants du solvant Tiflex, acétate de 1-méthoxy-2-propyle (MPA), par les radicaux OH et les atomes de Cl. En outre, les constantes de vitesse de réaction de OH et Cl avec une série d' acétates d’alcoxyle largement utilisés dans l'industrie du revêtement et la peinture, l'acétate de méthoxy-2-butyle (2MBA), l'acétate de méthoxy-3-butyle (3MBA), l'acétate de méthoxy-éthyle (MEA), l'acétate d'éthoxy-éthyle (EEE) et l’acétate de n-pentyle (n-PA), ont été déterminées. Les expériences ont été conduites en utilisant la technique de photolyse laser pulsée couplée à la fluorescence induite par laser, un réacteur à écoulement à basse pression couplé à un spectromètre de masse et une chambre de simulation atmosphérique couplé à GC-FID, FTIR et GC-MS en utilisant les méthodes absolue et relative. Les données cinétiques ont été utilisées pour déterminer les expressions Arrhenius pour évaluer le devenir environnemental des composés étudiés tels que leur durée de vie et le potentiel de formation d'ozone. D'autre part, le mécanisme réactionnel a été étudié et les principaux produits de dégradation et leurs rendements ont été déterminés en présence de NO. Les spectres d’absorption UV-Vis de MPA, 2MBA et 3MBA ont également été déterminés afin d'évaluer le potentiel de photolyse de ces composés dans l’atmosphère. Les paramètres cinétiques et mécanistiques ainsi que les durées de vie troposphérique déterminés sont utilisés comme données d'entrée dans les modèles de simulation atmosphériques photochimiques et dans les modèles de dispersion atmosphérique de produits chimiques pour évaluer leur impact atmosphériqueIn the context of DISPATMO project (forecast study of pollution risks related to the atmospheric dispersal of chemicals), risk studies linked to the fires and the explosions due to chemical storage were conducted. The purpose of this thesis was to perform a thorough kinetic and mechanistic study to determine the gas phase degradation of one of the main component of Tiflex solvent, the 1-methoxy 2-propyl acetate (MPA). Furthermore, the rate coefficients of OH and Cl with a series of alkoxy acetates widely used in painting and coating industries, 2-methoxy-butyl acetate (2MBA), 3-methoxybutyl acetate (3MBA), methoxy ethyl acetate (MEA), ethoxy ethyl acetate (EEA) and n-pentyl acetate (n-PA), were determined. The experiments were performed employing the pulsed laser photolysislaser induced fluorescence technique, a low pressure flow tube reactor coupled with a quadrupole mass spectrometer and an atmospheric simulation chamber coupled with a GC-FID, a FTIR and a GC-MS using complementary absolute and relative rate methods. The kinetic data were used to derive the Arrhenius expressions as well as to evaluate the environmental fate of the studied compounds such as their lifetimes and the Photochemical Ozone Creation Potential. Besides, the reaction mechanism was investigated, while the major degradation products and their yields were determined in presence of NO. In addition, the UV-Vis absorption cross sections of MPA, 2MBA and 3MBA were measured in order to evaluate their potential photolysis in the atmosphere. The investigation of the chemical processes and the tropospheric lifetimes of the compounds are used as input data in photochemical atmospheric simulation models and in chemical agent atmospheric dispersion models to evaluate their atmospheric impact
5
Zhang, Bochun. "Failure Mechanism Analysis and Life Prediction Based on Atmospheric Plasma-Sprayed and Electron Beam-Physical Vapor Deposition Thermal Barrier Coatings". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35709.
Testo completoAbstract (sommario):
Using experimentally measured temperature-process-dependent model parameters, the failure analysis and life prediction were conducted for Atmospheric Plasma Sprayed Thermal Barrier Coatings (APS-TBCs) and electron beam physical vapor deposition thermal barrier coatings (EB-PVD TBCs) with Pt-modified -NiAl bond coats deposited on Ni-base single crystal superalloys. For APS-TBC system, a residual stress model for the top coat of APS-TBC was proposed and then applied to life prediction. The capability of the life model was demonstrated using temperature-dependent model parameters. Using existing life data, a comparison of fitting approaches of life model parameters was performed. The role of the residual stresses distributed at each individual coating layer was explored and their interplay on the coating’s delamination was analyzed. For EB-PVD TBCs, based on failure mechanism analysis, two newly analytical stress models from the valley position of top coat and ridge of bond coat were proposed describing stress levels generated as consequence of the coefficient of thermal expansion (CTE) mismatch between each layers. The thermal stress within TGO was evaluated based on composite material theory, where effective parameters were calculated. The lifetime prediction of EB-PVD TBCs was conducted given that the failure analysis and life model were applied to two failure modes A and B identified experimentally for thermal cyclic process. The global wavelength related to interface rumpling and its radius curvature were identified as essential parameters in life evaluation, and the life results for failure mode A were verified by existing burner rig test data. For failure mode B, the crack growth rate along the topcoat/TGO interface was calculated using the experimentally measured average interfacial fracture toughness.
6
Moe, Brian J. "Estimating Growth and Mortality in Elasmobranchs: Are we doing it correctly?" NSUWorks, 2015. http://nsuworks.nova.edu/occ_stuetd/42.
Testo completoAbstract (sommario):
The instantaneous mortality rate (M) is an important parameter in elasmobranch management and conservation, but is difficult to estimate directly. Thus, indirect estimates based on relatively easily obtained life history parameters are commonly used. Many indirect methods incorporate one or more parameters from the von Bertalanffy growth model (VBGM), which is often criticized for its inability to describe changes in growth associated with maturity. The Lester growth model (LGM) is a biphasic alternative to the VBGM that incorporates trade-offs between reproduction, growth, and survival, and may therefore more accurately estimate M. I used published data from 29 elasmobranch species to compare the performance of the LGM to four conventional growth models and nine conventional methods for indirectly estimating M. For three species (Heterodontus portusjacksoni, Rhizoprionodon taylori, and Carcharhinus limbatus), I obtained direct estimates of M to evaluate the accuracy of indirect M methods. According to AICc, the LGM was the best fitting model for 80.8% of datasets. Using one-sample t-tests, I found that five indirect M methods (two of which are dependent on the LGM) consistently generated estimates of M that were in close agreement with direct estimates. The most common methods in elasmobranch literature appear to be overestimating M by factors of 1.34 – 1.91. However, further research is needed to verify these results across a wider range of species. Overall, I recommend using the LGM to describe the lifetime growth of sharks, and estimating M by averaging across five indirect methods.
7
Gurney, Kevin Robert. "The model lifetimes, band intensities, growth scenarios and atmospheric implications of substitute chlorofluorocarbons". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52912.
Testo completoAbstract (sommario):
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographical references (leaves 31-32).
by Kevin Robert Gurney.
M.S.
8
Brown, Alex. "The lifetimes and time-series of chlorine and fluorine containing gases from the atmospheric chemistry experiment". Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/5484/.
Testo completoAbstract (sommario):
The research presented in this thesis is focused around environmentally important chlorine- and fluorine-containing species. The work in this thesis was carried out using data from the ACE-FTS. This work is divided into four principle areas of research. The changes in the volume mixing ratio (VMR) of CCl4, CF4, CFC-11, CFC-12, CFC-113, CH3Cl, ClONO2, COF2, COCl2, COClF, HCFC-22, HCFC-141b, HCFC-142b, HCl, HF and SF6 between 2004 and 2010 in the tropics are presented. In addition to calculating the changes in the VMR of these species during this time, this work allowed a quick comparison between profiles from the new Version 3 ACE-FTS retrieval and from the 3D chemical transport model SLIMCAT. This work acted as a rough validation of these new retrieval schemes. The trends calculated from SLIMCAT and ACE-FTS are in generally in good agreement. They show decreases in CCl4, CFC-11, CFC-12, CFC-113 and CH3Cl and increases in CF4, HCFC-22, HCFC-141b and HCFC-142b. ACE-FTS shows no statistically significant change in COCl2 and COClF, whilst showing an increase in COF2. The total VMRs of stratospheric fluorine and chlorine have been calculated, allowing changes in the VMRs of total stratospheric fluorine and chlorine between 2004 and 2010 to be calculated. In addition to this, the changes in the global warming potential-weighted chlorine and fluorine are also presented. This value allows the radiative forcing effects of changes in the VMR of these species to be evaluated. In a similar manner the changes in the ozone depleting potential-weighted total chlorine are also presented. Total fluorine is increasing in all latitudes. Global Warming Potential-weighted fluorine is increasing at a mean rate of 3.85 ± 0.07 % per year in the Northern Hemisphere and 3.58 ± 0.07 % per year in the Southern Hemisphere. Radiative efficiency-weighted total fluorine show smaller increases of between 0.23 ± 0.11 % per year and 0.45 ± 0.11 % per year. In the short term the changes in fluorine-containing species is having a small climatological effect whilst in the long term these changes will have a more significant climatological effect. Total chlorine is decreasing in all latitude bands. Both the global warming potential- and radiative forcing-weighted chlorine is decreasing. Global warming potential-weighted chlorine is decreasing by 0.31 ± 0.08 % per year in the northern hemisphere and 0.23 ± 0.08 % per year in the southern hemisphere. The changes in radiative efficiency-weighted chlorine are smaller with decreases of 0.11 ± 0.04 % per year in the northern hemisphere and 0.06 ± 0.12 % per year in the southern hemisphere. When considered together these results suggest that in the short term there has been very little, if any, change in climatologically effective chlorine. However, in the long term the reduction in the emissions of long lived CFCs and halons will produce a small reduction in the climatological effect of chlorine containing species. Finally, the stratospheric lifetimes of CFC-12 (113 +(-) 26 (18) years), CCl4 (35 +(-) 11 (7) years), CH4 (195 +(-) 75 (42) years), CH3Cl (69 +(-) 65 (23) years) and N2O (123 +(-) 53 (28) years) have been calculated, by correlating the stratospheric VMR of the species of interest against the VMR of CFC-11 at the same altitude.
9
Woodcock, Kenneth Reginald Simon. "The chemistry of Fe+ and Fe-containing ions with atmospheric gases : implications for the lifetimes of sporadic E layers". Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435299.
Testo completo
10
Fakih, Mariam. "Réactivité atmosphérique des principaux produits d'oxydation de première génération des monoterpènes". Electronic Thesis or Diss., Reims, 2024. http://www.theses.fr/2024REIMS010.
Testo completoAbstract (sommario):
Les monoterpènes sont des composés organiques volatils biogéniques (COVB) largement émis dans l'atmosphère par les forêts et les cultures végétales, représentant ainsi des acteurs significatifs de la chimie atmosphérique. Leur réactivité importante envers les oxydants atmosphériques a fait sujet de plusieurs études dans la littérature. Cependant, leurs produits de première génération d’oxydation sont moins évalués et pourraient expliquer en partie la réactivité manquante ainsi que la sous-estimation de la formation des AOS par les modèles. Dans ce contexte, cette étude vise à comprendre la réactivité atmosphérique de cinq COVB (nopinone, myrténal, kétolimonène, caronaldéhyde, et limononaldéhyde) qui sont des produits de première génération de l’oxydation des α et β-pinène et du limonène. Ce travail porte sur l’étude des processus de dégradation en déterminant la cinétique et le mécanisme des réactions d'oxydation des COVB visés par le radical OH, le chlore et l’ozone, ainsi que leur potentielle de photolyse au travers de l’étude de leurs spectres d’absorption UV-Vis. Pour ce faire, les réactions d'oxydation des cinq produits de première génération d’oxydation de monoterpènes ont été étudiées en chambre de simulation atmosphérique couplée à différentes techniques analytiques (FTIR, SPME-GC/MS, PTR-MS-ToF).L’étude spectroscopique se concentre sur la détermination des spectres d’absorption UV-visible des cinq composés dans le domaine 200-400 nm à une température de 353 ± 2 K, et à une pression inférieure à la pression de vapeur saturante du COVB. Les spectres montrent une large bande d'absorption située entre 240 et 370 nm, correspondant à la bande n-π* du groupement carbonyle. L'absorption significative de ces composés au-delà de 290 nm suggère qu’ils sont susceptibles d'être décomposés par photolyse en quelques heures au minimum.Les études cinétiques en température réalisées dans cette thèse concernent la réaction (COV+ OH) pour le nopinone, le myrténal, le kétolimonène et le limononaldehdye, la réaction (COV + Cl) pour le nopinone, le myrténal et le kétolimonène et la réaction d’ozonolyse pour le kétolimonène, le myrténal et le limononaldéhyde. Les expériences ont été menées soit en utilisant la méthode cinétique relative ou la méthode cinétique absolue dans le domaine de température 298 – 353 K et à pression atmosphérique. Les résultats cinétiques obtenus ont permis de calculer les durées de vie atmosphérique de ces composés. Leur persistance atmosphérique ne dépasse pas une journée. Ces durées de vie montrent globalement que la principale voie d’élimination des composés étudiés est liée à leur réaction avec les radicaux OH avec une concurrence importante en région côtière des radicaux Cl. Par ailleurs, les études cinétiques en température ont mis en évidence une tendance générale positive avec l'augmentation de la température vis à vis des radicaux OH et de l’ozone et négative avec le chlore.Enfin des études mécanistiques d’ozonolyse concernant l’ozonolyse du kétolimonène, myrténal et limononaldéhyde ont été élaborées. Ces études consistent à suivre l’évolution temporelle des réactifs ainsi que leur produit de formation. Ces données nous ont permis d’extraire le taux de formation des produits formés lors des processus d’ozonolyse. En se basant sur ces résultats des mécanismes réactionnels d’ozonolyse du kétolimonène, myrténal et limononaldéhyde sont proposésMonoterpenes are biogenic volatile organic compounds (BVOCs) widely emitted into the atmosphere by forests and plant crops, thus representing significant players in atmospheric chemistry. Their high reactivity towards atmospheric oxidants has been the subject of several studies in the literature. However, their first-generation oxidation products are less evaluated, and could partly explain the missing reactivity and the underestimation of AOS formation by models. In this context, this study aims to understand the atmospheric reactivity of five VOCBs (nopinone, myrtenal, ketolimonene, caronaldehyde, and limononaldehyde) that are first-generation oxidation products of α- and β-pinene and limonene. This work focuses on the study of degradation processes by determining the kinetics and mechanism of oxidation reactions of the targeted BVOCs by the OH radical, chlorine and ozone, as well as their potential photolysis through the study of their UV-Vis absorption spectra. To this end, the oxidation reactions of five first-generation monoterpene oxidation products were studied in an atmospheric simulation chamber coupled with various analytical techniques (FTIR, SPME-GC/MS, PTR-MS-ToF).The spectroscopic study focused on determining the UV-visible absorption spectra of the five compounds in the 200-400 nm range at a temperature of 353 ± 2 K, and at a pressure below the saturation vapor pressure of COVB. The spectra show a broad absorption band between 240 and 370 nm, corresponding to the n-π* band of the carbonyl group. The significant absorption of these compounds above 290 nm suggests that they are likely to be removed by photolysis in at least a few hours.The temperature kinetic studies carried out in this thesis concern the (VOC+ OH) reaction for nopinone, myrtenal, ketolimonene and limononaldehdye, the (VOC + Cl) reaction for nopinone, myrtenal and ketolimonene and the ozonolysis reaction for ketolimonene, myrtenal and limononaldehyde. Experiments were carried out using either the relative or the absolute kinetic method in the temperature range 298 - 353 K and at atmospheric pressure. The kinetic results obtained made it possible to calculate the atmospheric lifetimes of these compounds. Their atmospheric persistence does not exceed one day. Overall, these lifetimes show that the main route of elimination for the compounds studied is through their reaction with OH radicals, with significant competition in coastal regions from Cl radicals. The study also revealed a generally positive trend for OH radicals and ozone with increasing temperature, and a negative trend for chlorine.Finally, mechanistic ozonolysis studies of ketolimonene, myrtenal and limononaldehyde were carried out. These studies consist of monitoring the temporal evolution of the reagents as well as the reaction product. These data allowed us to extract the formation rate of the products formed during ozonolysis processes. Based on these results, reaction mechanisms of ozonolysis of ketolimonene, myrtenal and limononaldehyde are proposed
Libri sul tema "Atmospheric lifetime"
1
United States. National Aeronautics and Space Administration., a cura di. The atmospheric lifetime experiment and the global atmospheric gas experiment (ALE/GAGE): Final report. [Washington, D.C.]: National Aeronautics and Space Administration, 1995.
Cerca il testo completo
2
Chance, Kelly, e Randall V. Martin. Line Shapes. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199662104.003.0006.
Testo completoAbstract (sommario):
Line shapes describe how absorption and emission are spectrally distributed around the line positions formed by rotational, vibrational, and electronic transitions. Line shapes arise from the different processes that spectrally broaden the absorption and emission of radiation. Optical thickness and equivalent width are shown to be fundamentally related to line shape. The fundamental line shape functions for atmospheres including the Gaussian line shape due to molecular motion and the Lorentzian line shape from lifetime broadening, including collision (pressure) broadening are described. Their convolution, the Voigt line shape, which is important in some atmospheric conditions is also described. The standard HITRAN database of spectroscopic parameters of molecules for use in calculation of radiative transfer in planetary atmospheres, from radiofrequencies to the near ultraviolet, is introduced.
3
Infrared radiative forcing and atmospheric lifetimes of trace species based on observations from UARS. [Washington, DC: National Aeronautics and Space Administration, 1997.
Cerca il testo completo
4
Infrared radiative forcing and atmospheric lifetimes of trace species based on observations from UARS. [Washington, DC: National Aeronautics and Space Administration, 1997.
Cerca il testo completo
5
Tibaldi, Stefano, e Franco Molteni. Atmospheric Blocking in Observation and Models. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228620.013.611.
Testo completoAbstract (sommario):
The atmospheric circulation in the mid-latitudes of both hemispheres is usually dominated by westerly winds and by planetary-scale and shorter-scale synoptic waves, moving mostly from west to east. A remarkable and frequent exception to this “usual” behavior is atmospheric blocking. Blocking occurs when the usual zonal flow is hindered by the establishment of a large-amplitude, quasi-stationary, high-pressure meridional circulation structure which “blocks” the flow of the westerlies and the progression of the atmospheric waves and disturbances embedded in them. Such blocking structures can have lifetimes varying from a few days to several weeks in the most extreme cases. Their presence can strongly affect the weather of large portions of the mid-latitudes, leading to the establishment of anomalous meteorological conditions. These can take the form of strong precipitation episodes or persistent anticyclonic regimes, leading in turn to floods, extreme cold spells, heat waves, or short-lived droughts. Even air quality can be strongly influenced by the establishment of atmospheric blocking, with episodes of high concentrations of low-level ozone in summer and of particulate matter and other air pollutants in winter, particularly in highly populated urban areas.Atmospheric blocking has the tendency to occur more often in winter and in certain longitudinal quadrants, notably the Euro-Atlantic and the Pacific sectors of the Northern Hemisphere. In the Southern Hemisphere, blocking episodes are generally less frequent, and the longitudinal localization is less pronounced than in the Northern Hemisphere.Blocking has aroused the interest of atmospheric scientists since the middle of the last century, with the pioneering observational works of Berggren, Bolin, Rossby, and Rex, and has become the subject of innumerable observational and theoretical studies. The purpose of such studies was originally to find a commonly accepted structural and phenomenological definition of atmospheric blocking. The investigations went on to study blocking climatology in terms of the geographical distribution of its frequency of occurrence and the associated seasonal and inter-annual variability. Well into the second half of the 20th century, a large number of theoretical dynamic works on blocking formation and maintenance started appearing in the literature. Such theoretical studies explored a wide range of possible dynamic mechanisms, including large-amplitude planetary-scale wave dynamics, including Rossby wave breaking, multiple equilibria circulation regimes, large-scale forcing of anticyclones by synoptic-scale eddies, finite-amplitude non-linear instability theory, and influence of sea surface temperature anomalies, to name but a few. However, to date no unique theoretical model of atmospheric blocking has been formulated that can account for all of its observational characteristics.When numerical, global short- and medium-range weather predictions started being produced operationally, and with the establishment, in the late 1970s and early 1980s, of the European Centre for Medium-Range Weather Forecasts, it quickly became of relevance to assess the capability of numerical models to predict blocking with the correct space-time characteristics (e.g., location, time of onset, life span, and decay). Early studies showed that models had difficulties in correctly representing blocking as well as in connection with their large systematic (mean) errors.Despite enormous improvements in the ability of numerical models to represent atmospheric dynamics, blocking remains a challenge for global weather prediction and climate simulation models. Such modeling deficiencies have negative consequences not only for our ability to represent the observed climate but also for the possibility of producing high-quality seasonal-to-decadal predictions. For such predictions, representing the correct space-time statistics of blocking occurrence is, especially for certain geographical areas, extremely important.
6
Çolak, Alper H., Simay Kirca e Ian D. Rotherham, a cura di. Ancient Woods, Trees and Forests. Pelagic Publishing, 2022. http://dx.doi.org/10.53061/kzad4079.
Testo completoAbstract (sommario):
As trees age, they become ecologically richer and more full of life. The process of a tree, wood or forest becoming ‘ancient’, however defined, involves a vast and subtle web of relations – among the trees themselves, with other organisms, with the wider landscape and with human beings. A single tree can provide a vast array of habitats which are an integral part of the complex co-evolutionary relationships evolved over its lifetime and later during its sometimes long afterlife. From ancient times until today, trees and woods have inspired artists, writers and scientists; they have shaped cultures and reverberated through belief systems. Yet worldwide, forest cover has declined dramatically over the last 1,000 years, and what remains has been more or less altered from its original condition. Today, ‘virgin forests’ are only to be found at a few sites unreachable by humans, and even then they are affected by climate change, atmospheric pollution and species extinctions. The aim of this book is to help an understanding of the web of connections relating to ancient trees and woodlands, and to offer techniques to ensure effective conservation and sustainability of this precious resource. This book considers the key issues from a range of different aspects and varied geographical locations, beginning with fundamental concepts and reflecting on the strengths and limitations of the idea of ancient trees. Individual chapters then deal with cultural heritage, the archaeology of trees, landscape history, forest rights, tree management, saproxylic insects, the importance of dead wood, practical conservation and monitoring, biodiversity, and wood pasture among many other themes. Fresh perspectives are put forward from across Europe as far as Turkey, as well as Great Britain. Overall, given the urgent need to discover, understand, conserve and restore ancient woodlands and trees, this publication will raise awareness, foster enthusiasm and inspire wonder.
Capitoli di libri sul tema "Atmospheric lifetime"
1
Nguyen, B. C., S. Belviso, B. Bonsang e G. Lambert. "Dimethyl Sulfide Lifetime in the Marine Atmosphere". In Physico-Chemical Behaviour of Atmospheric Pollutants, 434–39. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3841-0_48.
Testo completo
2
Mikkelsen, Robert L., e Terry L. Roberts. "Inputs: Potassium Sources for Agricultural Systems". In Improving Potassium Recommendations for Agricultural Crops, 47–73. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-59197-7_2.
Testo completoAbstract (sommario):
AbstractIn the potassium (K) cycle, inputs encompass all K sources that move into a given volume of soil. These inputs may include atmospheric deposition, irrigation water, runoff, erosion, as well as seeds, cuttings, and transplants. Accounting for all inputs is seldom routinely done on the farm. Many K inputs have variable concentrations, making estimations difficult. Estimates for added K are provided in some planning documents and can be used where testing of on-farm inputs is not feasible, although testing is preferred. Standard commercial fertilizers have known concentrations of K and are concentrated enough to be economical to transport long distances. The global reserves for their production have an estimated lifetime of thousands of years. This chapter emphasizes considerations for using various commercial fertilizer sources.
3
Owens, John G. "Calculation of the Global Warming Potential for Sulfur Hexafluoride Using the Updated Atmospheric Lifetime from Moore, et al." In Gaseous Dielectrics IX, 91–92. Boston, MA: Springer US, 2001. http://dx.doi.org/10.1007/978-1-4615-0583-9_12.
Testo completo
4
Perdomo Echenique, Enrique Alejandro, e Franziska Hesser. "Understanding Soil Organic Carbon Dynamics of Short Rotation Plantations After Land Use Change—From Establishment to Recultivation". In Sustainable Production, Life Cycle Engineering and Management, 65–84. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-29294-1_5.
Testo completoAbstract (sommario):
AbstractThe increase in soil organic carbon (SOC) stocks has the potential to contribute to climate mitigation strategies by reducing atmospheric CO2. Short rotation plantations (SRP) provide bio-based resources and can possibly accumulate SOC. Estimating the potential SOC stocks of short rotation plantations can help decision-makers to implement strategies that reduce SOC loss and thus contribute to climate change mitigation. The dynamic changes in SOC were estimated for a case study using the RothC carbon turnover model. The results indicate that SOC stocks increased from 37.8 to 48.52 t C/ha within 20 years of the plantation’s lifetime. Thus, an annual average increase of 0.535 t C/ha year is expected. Given the importance of implementing strategies that support the potential climate mitigation benefits of SRP, a sensitivity analysis was employed to identify the relevant factors that affected SOC prediction. For instance, the influence of soil condition heterogeneity, such as clay content, can vary the estimations of SOC accumulated. This highlights the relevance of obtaining primary data at different locations within the plantation’s areas: to obtain a variety of SOC stock estimations that give a better representation of SOC accumulation. Such analysis help to propose suggestions that mitigate the climate effect of short rotation plantations.
5
Harrison, Roy M. "Chemistry of the Troposphere". In Pollution: Causes, Effects and Control, 182–203. The Royal Society of Chemistry, 2013. http://dx.doi.org/10.1039/bk9781849736480-00182.
Testo completoAbstract (sommario):
The concept of pollutant cycling in the atmosphere is introduced in this chapter and the basic determinants of atmospheric lifetime and concentration variability described. The hydroxyl radical is central to atmospheric chemistry and its formation pathways are discussed leading into a description of the formation chemistry and behaviour of tropospheric ozone. A subsequent description of other atmospheric oxidants (peroxyacetylnitrate and oxides of nitrogen) is followed by a consideration of the sources and sinks of atmospheric acids and bases. Amongst the most important constituents in the atmosphere in relation to human health and climate regulation are atmospheric aerosols whose typical composition and formation pathways are outlined. Finally, the inter-relationships between pollutants, environmental effects and impacts in relation to climate, eco-systems and human health are presented.
6
Whiteman, C. David. "Atmospheric Scales of Motion and Atmospheric Composition". In Mountain Meteorology. Oxford University Press, 2000. http://dx.doi.org/10.1093/oso/9780195132717.003.0010.
Testo completoAbstract (sommario):
Weather phenomena occur over a very broad range of scales of space and time, from the global circulation systems that extend around the earth’s circumference to the small eddies that cause cigarette smoke to swirl and mix with clear air. Each circulation can be described in terms of its approximate horizontal diameter and lifetime. Large-scale weather systems, such as hemispheric wave patterns called Rossby waves, monsoons, high and low pressure centers, and fronts, are called synopticscale weather systems. Temperature, humidity, pressure, and wind measurements collected simultaneously all over the world are used to analyze and forecast the evolution of these systems, which have diameters greater than 200 km (125 mi) and lifetimes of days to months. Mesoscale weather events include diurnal wind systems such as mountain wind systems, like breezes, sea breezes, thunderstorms, and other phenomena with horizontal scales that range from 2 to 200 km (1 to 125 mi) and lifetimes that range from hours to days. Mesoscale meteorologists use networks of surface- based instruments, balloon-borne sounding systems, remote sensing systems (e.g., radar, lidar, and sodar), and aircraft to make observations on these scales. Microscale meteorology focuses on local or small-scale atmospheric phenomena with diameters below 2 km (1 mi) and lifetimes from seconds to hours, including gusts and turbulence, dust devils, thermals, and certain cloud types. Microscale studies are usually confined to the layer of air from the earth’s surface to an altitude where surface effects become negligible (approximately 1000 feet or 300 m at night and 5000 feet or 1500 m during the day). A fourth and less rigorously defined term, the regional scale, denotes circulations and weather events occurring on horizontal scales from 500 to 5000 km (310 to 3100 mi). The regional scale is thus smaller than synoptic scale, but larger than mesoscale. The term is often used to describe events that occur within more or less homogeneous physiographic provinces (e.g., the Pacific Northwest region). Major mountain ranges impact the weather on the synoptic scale. They anchor large-scale pressure systems in the Northern Hemisphere, cause low and high pressure weather systems to form, and produce large-scale seasonal wind systems in Asia and North America.
7
Holland, Elisabeth A., G. Philip Robertson, James Greenberg, Peter M. Groffman e Richard D. Boone James R. Gosz. "Soil CO2, N20, and CH4 Exchange". In Standard Soil Methods for Long-Term Ecological Research, 185–202. Oxford University PressNew York, NY, 1999. http://dx.doi.org/10.1093/oso/9780195120837.003.0010.
Testo completoAbstract (sommario):
Abstract The composition of the earth’s atmosphere is largely determined by the exchange of trace gases with the oceanic and terrestrial biosphere. Human-induced perturbations to the earth’s system are changing the atmospheric composition at unprecedented rates. The gases of particular interest can be divided into two categories: those species that are radiatively active and thus influence the radiation balance of the earth (the so-called greenhouse gases: nitrous oxide [N2O], carbon dioxide [CO2], methane [CH4], chlorofluorocarbons [CFCs}, halogenated chlorofluorocarbons [HCFCs}, and ozone [03)), and those species that are photochemically active and thus influence the troposphere’s ability to cleanse itself (its “‘oxidizing capacity”‘: hydroxyl radical OH, hydroperoxy radical HO2, 03, active nitrogen (NOx-NO + NO2), carbon monoxide [CO], CH4, and volatile organic carbon compounds other than methane [VOCs]). The atmospheric lifetime of the radiatively active species is often longer than 10 years, extending to as long as 120 years for N2O in the troposphere (the lower 10-16 km of the atmosphere), whereas the lifetime of the photochemically active species is 1-3 days (Tab. l 0.1). Because of their very long lifetimes, N2O, CFCs, HCFCs, and other halogenated compounds persist long enough to be transported to the stratosphere, where they play an important role in stratospheric ozone depletion. Some gases, notably 03 and CH4, are both photochemically and radiatively active. Both radiatively active and photochemically active gases are central to global change research; these gases are rapidly altering atmospheric composition and chemistry, in part as a result of changes in biospheric activity.
8
Taylor, F. W. "The ozone layer". In Elementary Climate Physics, 119–29. Oxford University PressOxford, 2005. http://dx.doi.org/10.1093/oso/9780198567332.003.0008.
Testo completoAbstract (sommario):
Abstract Nevertheless, it is still one of the more important minor constituents of the atmosphere. One reason is because ozone has more strong absorption bands in the ultraviolet (UV) than the other common atmospheric gases, and so it dominates radiative transfer in this part of the spectrum. It also has important bands in the infrared. Ozone is extremely chemically active, as a result of which it plays a key role in determining the amounts of other constituents with which it reacts. It follows that ozone will be fairly short-lived; in the stratosphere, the lifetime of a typical atmospheric ozone molecule is just marginally longer than the diurnal cycle, at 1 to 2 days.
9
Calvert, Jack, Abdelwahid Mellouki, John Orlando, Michael Pilling e Timothy Wallington. "Rate Coefficients and Mechanisms for the Atmospheric Oxidation of the Aldehydes". In Mechanisms of Atmospheric Oxidation of the Oxygenates. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199767076.003.0007.
Testo completoAbstract (sommario):
Aldehydes are emitted from a variety of anthropogenic sources associated with natural gas and petroleum combustion (for examples, see tables I-C-2 and I-C-3). Winer et al. (1992) have discussed direct emissions of aldehydes from biogenic sources. They are also important intermediates in the oxidation of directly emitted organic compounds. For example, formaldehyde, CH2O formed in the reaction of CH3O with O2 . . . CH3O + O2 → CH2O + HO2 . . . CH3O is formed in the oxidation of methane, and a number of other compounds. There are also many other sources of CH2O; for example, the Leeds University’s Master Chemical Mechanism (MCM) lists a total of ∼ 140 CH2O precursors: http://mcm.leeds.ac.uk/MCM/. Aldehydes with saturated hydrocarbon chains (termed alkanals or acyclic aldehydes) react mainly with OH during the day and with NO3 at night. The aldehydic C—H bond is weaker than those in the hydrocarbon chain; and, certainly for the shorter carbon chain species, abstraction by both OH and NO3 occurs primarily at the aldehydic center to form an acyl radical which reacts rapidly with O2 to form an acylperoxy radical, e.g., . . . CH3CHO + OH → CH3CO + H2O . . . . . . CH3CO + O2 → CH3C(O)O2 . . . An important reaction of the acylperoxy radical is with NO2 to form an acylperoxy nitrate. In the example shown, the oxidation of acetaldehyde gives acetyl peroxy radicals which can react with NO2 to form peroxyacetyl nitrate, CH3C(O)O2NO2, generally known as PAN: . . . CH3C(O)O2 + NO2 → CH3C(O)O2NO2 . . . Peroxyacyl nitrates dissociate quite quickly at 298 K, to regenerate peroxyacyl radicals. For example, PAN has a lifetime of about 50 min. The lifetime increases rapidly at the lower temperatures experienced at higher altitudes and is several months at the temperatures (∼ 250 K) of the upper troposphere. This long lifetime provides a mechanism for the transport of NOx from polluted areas to less polluted areas, by transfer of peroxyacyl nitrates from the boundary layer to the free troposphere; subsequent subsidence can return them to the boundary layer where they dissociate at the higher temperatures encountered there. The atmospheric reactions of the nitrates are discussed in detail in chapters VIII and IX.
10
Kaimal, J. C., e J. J. Finnigan. "Spectra and Cospectra Over Flat Uniform Terrain". In Atmospheric Boundary Layer Flows. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195062397.003.0005.
Testo completoAbstract (sommario):
Turbulent flows like those in the atmospheric boundary layer can be thought of as a superposition of eddies—coherent patterns of velocity, vorticity, and pressure— spread over a wide range of sizes. These eddies interact continuously with the mean flow, from which they derive their energy, and also with each other. The large “energy-containing” eddies, which contain most of the kinetic energy and are responsible for most of the transport in the turbulence, arise through instabilities in the background flow. The random forcing that provokes these instabilities is provided by the existing turbulence. This is the process represented in the production terms of the turbulent kinetic energy equation (1.59) in Chapter 1. The energy-containing eddies themselves are also subject to instabilities, which in their case are provoked by other eddies. This imposes upon them a finite lifetime before they too break up into yet smaller eddies. This process is repeated at all scales until the eddies become sufficiently small that viscosity can affect them directly and convert their kinetic energy to internal energy (heat). The action of viscosity is captured in the dissipation term of the turbulent kinetic energy equation. The second-moment budget equations presented in Chapter 1, of which (1.59) is one example, describe the summed behavior of all the eddies in the turbulent flow. To understand the conversion of mean kinetic energy into turbulent kinetic energy in the large eddies, the handing down of this energy to eddies of smaller and smaller scale in an “eddy cascade” process, and its ultimate conversion to heat by viscosity, we must isolate the different scales of turbulent motion and separately observe their behavior. Taking Fourier spectra and cospectra of the turbulence offers a convenient way of doing this. The spectral representation associates with each scale of motion the amount of kinetic energy, variance, or eddy flux it contributes to the whole and provides a new and invaluable perspective on boundary layer structure. The spectrum of boundary layer fluctuations covers a range of more than five decades: millimeters to kilometers in spatial scales and fractions of a second to hours in temporal scales.
Atti di convegni sul tema "Atmospheric lifetime"
1
Manninen, R. P. J., e Kari U. Kaila. "Lifetime of the O(1S) excitation state". In Twenty-third European Meeting on Atmospheric Studies by Optical Methods, a cura di Vasily N. Ivchenko. SPIE, 1997. http://dx.doi.org/10.1117/12.284770.
Testo completo
2
Pruis, Matthew, e Donald Delisi. "Correlation of the Temporal Variability in the Crosswind and the Observation Lifetime of Vortices Measured with a Pulsed Lidar". In 3rd AIAA Atmospheric Space Environments Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2011. http://dx.doi.org/10.2514/6.2011-3199.
Testo completo
3
Jarligo, M. O., D. E. Mack, G. Mauer, R. Vaßen e D. Stöver. "Atmospheric Plasma Spraying of High Melting Temperature Complex Perovskites for TBC Application". In ITSC2009, a cura di B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima e G. Montavon. ASM International, 2009. http://dx.doi.org/10.31399/asm.cp.itsc2009p0065.
Testo completoAbstract (sommario):
Abstract In this investigation, two complex perovskite powders, Ba(MgTa)O and Ta(AlMgT)O, are deposited by atmospheric plasma spraying and evaluated for use as thermal barrier layers. Process parameters are optimized to provide sufficient melting without causing the formation of secondary phases. Deposited coatings are assessed based on composition, morphology, porosity, and thermal cycling lifetime. It is shown that the nature of the starting powders has a significant effect on the lifetime and performance of perovskite-based thermal barrier coatings.
4
Lai, David, Don Jacob, Fiona Lo e Donald Delisi. "Assessment of Pulsed Lidar Measurements of Aircraft Wakes Using a Lidar Simulator: Vortex Position Estimates for IGE, Linking, and Oblique Viewing, and Dependence of Vortex Lifetime on SNR". In 3rd AIAA Atmospheric Space Environments Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2011. http://dx.doi.org/10.2514/6.2011-3197.
Testo completo
5
Fehsenfeld, Fred C. "Trace species in the atmosphere: air quality problems and measurement requirements and validation". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.wz1.
Testo completoAbstract (sommario):
There is evidence that air quality on a global scale is threatened by the systematic change in the atmospheric concentration of a variety of trace compounds. These compounds range from those that are not chemically reactive in the lower atmosphere (troposphere), such as the chlorofluoromethanes (CFM), to very reactive compounds, such as the oxides of nitrogen (NO x ) and the nonmethane hydrocarbons (NMHC). Although all the compounds cause significant problems concerning air quality on a regional or even global scale, the type of data required to obtain the necessary information concerning their atmospheric distribution depends strongly on the chemical reactivity (lifetime) of the compounds in the atmosphere. To monitor the concentrations of and understand the processes involving these compounds, very sensitive and/or precise measurement techniques are required. Specifically, these techniques may be required to detect less than one part per billion of the compound of interest or have a precision of one part in 104. The air quality problems associated with these compounds are outlined and the instrument needs and requirements for the measurement of the compounds are briefly discussed. Finally, the current approach to the validation of measurement techniques is described.
6
Dong, H., G. J. Yang, H. Ding, C. X. Li e C. J. Li. "The Influence of Temperature Gradient on Thermal Cyclic Lifetime of Plasma-Sprayed Thermal Barrier Coatings". In ITSC 2014, a cura di R. S. Lima, A. Agarwal, M. M. Hyland, Y. C. Lau, G. Mauer, A. McDonald e F. L. Toma. DVS Media GmbH, 2014. http://dx.doi.org/10.31399/asm.cp.itsc2014p0794.
Testo completoAbstract (sommario):
Abstract Thermal cycling tests were performed on thermal barrier coatings (TBCs) to evaluate the influence of temperature gradients in the ceramic topcoat on overall lifetime and performance. The coating system tested consists of an Inconel 738 substrate, a cold-sprayed NiCoCrAlTaY bond coat, and an atmospheric plasma sprayed YSZ topcoat. YSZ surface temperatures were 1150, 1200, and 1250 °C, corresponding to temperature gradients of 150, 200, and 250 °C across the 250 µm thick layer. Heating and cooling times were set at 120 sec for each thermal cycle. The results of the study show that lifetime decreases with increasing temperature gradient, although the gradient has little effect on the failure mode.
7
Gupta, M., K. Skogsberg e P. Nylén. "Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime in Thermal Barrier Coatings". In ITSC2013, a cura di R. S. Lima, A. Agarwal, M. M. Hyland, Y. C. Lau, G. Mauer, A. McDonald e F. L. Toma. ASM International, 2013. http://dx.doi.org/10.31399/asm.cp.itsc2013p0596.
Testo completoAbstract (sommario):
Abstract In previous work, it was observed that atmospheric plasma sprayed bond coats perform better than their HVOF counterparts, which is contrary to current literature data. The objective of this work is to understand the observed difference with the aid of finite-element modeling. Different thermally grown oxide layer thicknesses and surface topographies are evaluated and the modeling results are compared with current theories based on simplified sinusoidal profiles. It is shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.
8
Dong, Hui, Chang-Jiu Li, Hang Ding, Guan-Juan Yang e Cheng-Xin Li. "Effect of MCrAlY Bond Coat Temperature on Thermal Cyclic Lifetime of Plasma-Sprayed Thermal Barrier Coatings". In ITSC2015, a cura di A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen e C. A. Widener. ASM International, 2015. http://dx.doi.org/10.31399/asm.cp.itsc2015p0795.
Testo completoAbstract (sommario):
Abstract Gradient thermal cycling test was performed on atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) to examine the influence of the bond coat temperature on the thermal cyclic lifetime. The TBC system consisted of Inconel 738 substrate, cold-sprayed NiCoCrAlTaY bond coat (BC) and plasma-sprayed yttria-stabilized zirconia (YSZ) top coat. Every thermal cycling test included 70s heating, 50s holding and 120s cooling. The temperature of top YSZ surface was about 1150 °C, while the bond coat temperatures were 900°C, 950°C and 1000°C, respectively. Results indicated that the lifetime of APS TBCs is significantly affected by bond coat temperature. A model to predict the relative thermal cyclic lifetime of TBCs at different bond coat temperature was established by taking account of main factors affecting the lifetime of TBCs. It was found that the predicted results are consistent with the observed results. As a result, the change of lifetime of APS TBCs mainly depends on the growth rate of thermally grown oxide (TGO), elastic modulus of YSZ and thermal expansion mismatch difference between YSZ and substrate caused by different bond coat temperature.
9
Hu, Hui, e Zheyan Jin. "Unsteady Heat Transfer and Phase Changing Process Within Small Icing Water Droplets". In ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer. ASMEDC, 2009. http://dx.doi.org/10.1115/mnhmt2009-18118.
Testo completoAbstract (sommario):
We report progress made in our recent effort to develop and implement a novel, lifetime-based molecular tagging thermometry (MTT) technique to quantify unsteady heat transfer and phase changing process inside small icing water droplets pertinent to wind turbine icing phenomena. The lifetime-based MTT technique was used to achieve temporally-and-spatially resolved temperature distribution measurements within small, convectively-cooled water droplets to quantify unsteady heat transfer within the small water droplets in the course of convective cooling process. The transient behavior of phase changing process within small icing water droplets was also revealed clearly by using the lifetime-based MTT technique. Such measurements are highly desirable to elucidate underlying physics to improve our understanding about important micro-physical phenomena pertinent to ice formation and accreting process as water droplets impinging onto wind turbine in cold atmospheric environment.
10
Alaruri, Sami, e Andy Brewington. "High-Temperature Surface Measurements of Turbine Engine Components Using Thermographic Phosphors". In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-368.
Testo completoAbstract (sommario):
A laser-based system for single point high-temperature measurements of turbine engine component surfaces coated with thermographic phosphors is described. Decay lifetime calibration measurements obtained for Y2O3:Eu over the temperature range ∼530–1000°C are presented. Further, the results obtained from a coupon placed in the outlet gas flow of an atmospheric-combustor are described.
Rapporti di organizzazioni sul tema "Atmospheric lifetime"
1
Hart, Carl, e Gregory Lyons. A tutorial on the rapid distortion theory model for unidirectional, plane shearing of homogeneous turbulence. Engineer Research and Development Center (U.S.), luglio 2022. http://dx.doi.org/10.21079/11681/44766.
Testo completoAbstract (sommario):
The theory of near-surface atmospheric wind noise is largely predicated on assuming turbulence is homogeneous and isotropic. For high turbulent wavenumbers, this is a fairly reasonable approximation, though it can introduce non-negligible errors in shear flows. Recent near-surface measurements of atmospheric turbulence suggest that anisotropic turbulence can be adequately modeled by rapid-distortion theory (RDT), which can serve as a natural extension of wind noise theory. Here, a solution for the RDT equations of unidirectional plane shearing of homogeneous turbulence is reproduced. It is assumed that the time-varying velocity spectral tensor can be made stationary by substituting an eddy-lifetime parameter in place of time. General and particular RDT evolution equations for stochastic increments are derived in detail. Analytical solutions for the RDT evolution equation, with and without an effective eddy viscosity, are given. An alternative expression for the eddy-lifetime parameter is shown. The turbulence kinetic energy budget is examined for RDT. Predictions by RDT are shown for velocity (co)variances, one-dimensional streamwise spectra, length scales, and the second invariant of the anisotropy tensor of the moments of velocity. The RDT prediction of the second invariant for the velocity anisotropy tensor is shown to agree better with direct numerical simulations than previously reported.
2
Gasim, Anwar, Lester Hunt e Jeyhun Mikayilov. Methane Emissions Baseline Forecasts for Saudi Arabia Using the Structural Time Series Model and Autometrics. King Abdullah Petroleum Studies and Research Center, maggio 2023. http://dx.doi.org/10.30573/ks--2023-dp08.
Testo completoAbstract (sommario):
Reducing methane (CH4) emissions is key to near-term efforts to limit global warming. CH4 is the second most abundant anthropogenic greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO2). The production, transport, and consumption of fossil fuels, in addition to waste and agriculture, account for most anthropogenic CH4 emissions globally (IPCC 2018). Although CH4has only a 12-year lifetime in the atmosphere, it is 84 times more potent per ton than CO2 in a 20-year period and 28 times more potent in a 100-year period (IPCC 2018). The drastically stronger short-term potency of CH4 explains why its short-term impact on global warming is considerably greater than that of CO2. Therefore, meeting the goals of the Paris Agreement necessitates not only decarbonization but also significant CH4 emissions reductions, especially in the near term.
3
Simmons. L51814 Survey Of Dry Low NOx Combustor Experience. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), settembre 1999. http://dx.doi.org/10.55274/r0010207.
Testo completoAbstract (sommario):
Air pollution has become a major public issue and it is now evident that unburned hydrocarbons, CO, and NOx must meet increasingly restrictive standards. The emissions of nitrogen oxides by gas turbines are of concern because of their high toxicity and their role in the formation of photochemical smog. The formation of NOx occurs in a gas-fired gas turbine when combustion temperatures exceed a critical level for sufficient time to allow atmospheric nitrogen and oxygen to combine. For those gas turbine applications where steam or ultra-pure water are readily available, then steam or water injection are preferable NOx control strategies. Because these attributes are usually not available at pipeline compression stations, the turbine operators in the pipeline industry have chosen to control emissions by a dry combustion process. An alternative would be a catalytic reduction of the NOx generated in the exhaust gas but this requires an investment in SCR hardware and continuous use of ammonia, which adds to operating costs. Historically, dry low emissions (DLE) systems have experienced a greater than expected number of start-up problems as new products were introduced to the marketplace. A need of the gas pipeline industry is to identify the operating problems experienced with DLE systems, to link these problems to their most probable cause, to estimate costs incurred, and to glean strategies for avoiding future problems. A comprehensive PRCI sponsored survey of operators and manufacturers was completed which provides assistance to gas turbine operators in making NOx control procurement decisions and for budgeting operations and maintenance costs. This first ever detailed study provides information on typical operating costs and problems incurred with the currently operating DLE systems and serves as a guide for individual companies in the selection of cost effective low NOx combustion systems from available components offered by the OEM and after-market suppliers. The information developed by this report is intended to guide operators in estimating maintenance and repair costs to establish a lifetime cost of operation.
4
EGR Cooler Fouling Reduction: A New Method for Assessment in Early Engine Development Phase. SAE International, marzo 2022. http://dx.doi.org/10.4271/022-01-0589.
Testo completoAbstract (sommario):
High pressure EGR provides NOx emission reduction even at low exhaust temperatures. To maintain a safe EGR system operation over a required lifetime, the EGR cooler fouling must not exceed an allowable level, even if the engine is operated under worst-case conditions. A reliable fouling simulation model represents a valuable tool in the engine development process, which validates operating and calibration strategies regarding fouling tendency, helping to avoid fouling issues in a late development phase close to series production. Long-chained hydrocarbons in the exhaust gas essentially impact the fouling layer formation. Therefore, a simulation model requires reliable input data especially regarding mass flow of long-chained hydrocarbons transported into the cooler. There is a huge number of different hydrocarbon species in the exhaust gas, but their individual concentration typically is very low, close to the detection limit of standard in-situ measurement equipment like GC-MS. Therefore, a new measurement and analysis approach has been developed, where the exhaust gas is guided to a metal foam collector, in which HC`s are deposited. The probe is then analyzed in a suited thermogravimetrical system (TGA) in nitrogen atmosphere, temperature range 25°C to 650°C. Analyzing the TGA curve, HC concentration data for 6 different boiling temperature ranges are obtained, provided to an adapted 1-d fouling simulation model. Using these data along with further input parameters like cooler geometry, gas temperature, pressure, flow, particle size distribution and coolant temperature, the simulation model has proven as a suitable tool to predict the fouling and identify engine settings for fouling reduction.