Article

Aviation and global climate change in the 21st century

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Abstract

Aviation emissions contribute to the radiative forcing (RF) of climate. Of importance are emissions of carbon dioxide (CO2), nitrogen oxides (NOx), aerosols and their precursors (soot and sulphate), and increased cloudiness in the form of persistent linear contrails and induced-cirrus cloudiness. The recent Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) quantified aviation’s RF contribution for 2005 based upon 2000 operations data. Aviation has grown strongly over the past years, despite world-changing events in the early 2000s; the average annual passenger traffic growth rate was 5.3% yr-1 between 2000 and 2007, resulting in an increase of passenger traffic of 38%. Presented here are updated values of aviation RF for 2005 based upon new operations data that show an increase in traffic of 22.5%, fuel use of 8.4% and total aviation RF of 14% (excluding induced-cirrus enhancement) over the period 2000–2005. The lack of physical process models and adequate observational data for aviationinduced cirrus effects limit confidence in quantifying their RF contribution. Total aviation RF (excluding induced cirrus) in 2005 was ~55mW m-2 (23–87mW m-2, 90% likelihood range), whichwas 3.5% (range 1.3–10%, 90% likelihood range) of total anthropogenic forcing. Including estimates for aviation-induced cirrus RF increases the total aviation RF in 2005–78 mW m-2 (38–139 mW m-2, 90% likelihood range), which represents 4.9% of total anthropogenic forcing (2–14%, 90% likelihood range). Future scenarios of aviation emissions for 2050 that are consistent with IPCC SRES A1 and B2 scenario assumptions have been presented that show an increase of fuel usage by factors of 2.7–3.9 over 2000. Simplified calculations of total aviation RF in 2050 indicate increases by factors of 3.0–4.0 over the 2000 value, representing 4–4.7% of total RF (excluding induced cirrus). An examination of a range of future technological options shows that substantive reductions in aviation fuel usage are possible only with the introduction of radical technologies. Incorporation of aviation into an emissions trading system offers the potential for overall (i.e., beyond the aviation sector) CO2 emissions reductions. Proposals exist for introduction of such a system at a European level, but no agreement has been reached at a global level.

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... In addition, the continuous increase in the demand for air travel is also the main reason for the growth in carbon emissions (McCollum and Yang, 2009). The aviation industry is likely to achieve the emission-reduction target by joining the emission trading system and using revolutionary technologies (Chao et al., 2019;Lee et al., 2009). Luo et al. (2017) have conducted an in-depth comparative study of the characteristics and driving forces of CO 2 emissions from the freight sector in three regions of China from 1990 to 2007. ...
... Technological improvements can effectively reduce the cost of alternative fuels. Mature application of such technologies is the most direct and effective way to reduce carbon emissions in the aviation industry (Lee et al., 2009). Therefore, the classification here only clearly highlights some key factors and does not mean that the remaining factors are unimportant. ...
... Air transport structure/effects of structural changes (Yu et al., 2020) If the impact of transportation structure factors can be effectively utilized, and if the government can promote structural optimization in route planning, design, and management, it will go a long way in helping China's civil aviation industry reduce its emissions. Flight diversion strategy (Teoh et al., 2020) Minimize flight path Regulatory approach to air travel practices (Higham et al., 2016) The supervision means can control the management level Route choice (Sobieralski, 2021) The optimal choice of route can reduce energy consumption Operational efficiency (Sgouridis et al., 2011) The improvement of efficiency in all aspects helps the aviation industry operate at the optimal level of energy consumption System efficiency (Lee et al., 2009) Management Sharing of transport services/sharing model (Wang et al., 2011) The improvement of efficiency in all aspects helps the aviation industry operate at the optimal level of energy consumption Propulsion efficiency (Sobieralski, 2021) Technology Technical efficiency/advances in technology/technical progress/pure technical efficiency/technological change Technical efficiency is a key factor in reducing emissions ...
Article
The international aviation industry is one of the fastest growing industries, resulting in an increase of greenhouse gas emissions. Controlling aviation carbon emissions is needed to further prevent future climate change as the demand for aviation continues to expand. Effective ways should be taken to control aviation carbon emissions, namely identifying the set of driving factors behind the carbon emissions, as well as, exploring low-carbon technologies in aviation. However, few studies have systematically identified the driving factors and given a timeline list of aviation low-carbon technologies. Therefore, from the life cycle perspective (including the aircraft designing, operating, and recovery), this paper applies text mining and literature metrology to identify the driving factors systematically. Moreover, an evaluation model is established to present the prioritization of factors, and the Delphi method is applied to create a timeline list of the low-carbon technologies in the aviation industry. The results show that demand, technological improvement, and alternative fuels are the most important factors affecting carbon emissions in the aviation industry, with their contribution percentages of 16 %, 14 %, and 12 %, respectively. In the short term, aviation relies more on policies to reduce emissions (supported by 79 % of experts). In the long term, technological progress enables the production of increasingly mature alternative fuels as well as reduces production costs. Among the set of experts, 74 % support strategies relating to renewable fuel and low carbon technologies as the main factors for the aviation industry to reduce carbon emissions.
... Aircraft emit particles and gases primarily in the form of carbon dioxide (CO 2 ), nitrogen oxides (NO x ), sulfur oxides (SO x ), water vapor (H 2 O) and soot [3]. Such emissions overall contribute to the climate change and have an important influence on the quality of air and human health [4]. The Intergovernmental Panel on Climate Change (IPCC) estimated that air transport contribution to the total radiative forcing accounts for 3.5% of the total anthropogenic agents [4]. ...
... Such emissions overall contribute to the climate change and have an important influence on the quality of air and human health [4]. The Intergovernmental Panel on Climate Change (IPCC) estimated that air transport contribution to the total radiative forcing accounts for 3.5% of the total anthropogenic agents [4]. Although aviation does not represent the main driver of the climate change, its contribution to the global warming remains remarkable and is required to be reduced. ...
... where M = U /c 0 is the Mach number, k = ω/c 0 and β 2 = 1 − M 2 . Each mode is defined by the two indices n and j , which represents the number of azimuthal lobes and radial 4 An annular duct, namely a cylindrical duct with a center body, can be used to approximately represent the bypass duct of a turbofan engine, while a simple cylindrical duct without a center body can be associated to the duct upstream the fan. 5 All the quantities in Eq. (2.10) are determined by the duct geometry, while the modal coefficients ± n j are related to the noise sources inside the duct [70]. 2. SOURCES OF NOISE IN OPEN ROTORS AND TURBOFANS nodes, respectively, while the amplitude of a certain mode along the radial coordinate is given by P n j (r ). ...
Thesis
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The accurate and reliable prediction of the aerodynamic noise sources of open rotors and ducted-fans in electric Vertical Take-Off and Landing (eVTOL) and non-conventional aircraft configurations is a challenging task from a computational perspective. Indeed, such propulsive systems can often operate in highly distorted and non-homogeneous flows, with the rotating blades interacting with strongly non-uniform and turbulent flows; and/or experience phenomena related to low Reynolds numbers and boundary-layer transition, due to the relatively small diameters and blade tip speeds. While analytical, semi-empirical and low-fidelity numerical models can provide quick and computationally inexpensive predictions, their results are often not fully reliable and their state-of-the-art requires a further development step to properly address the problem of rotor noise prediction in non-conventional aircraft and rotorcraft. On the other hand, Navier-Stokes based scale-resolving approaches such as Large Eddy Simulation (LES) have the capability to capture most of the aforementioned phenomena, but at a prohibitive computational cost for a routine employment in the design stages of such innovative vehicles. In view of this, high-fidelity scale-resolving lattice-Boltzmann numerical simulations, coupled with the Ffowcs Williams & Hawkings' acoustic analogy, are extensively performed and validated in this thesis with the aim of identifying, characterizing and predicting the primary sources of aerodynamic noise associated to open rotors/propellers and ducted-fans in eVTOL and novel aircraft configurations. First, the problem of broadband rotor trailing-edge and its reduction is addressed at airfoil level for a cambered profile operating at moderate Reynolds numbers and undergoing natural boundary-layer transition, by considering both a straight trailing-edge and serrated trailing-edges at different flap angles. For the straight trailing-edge cases, the numerical results compare favorably against the experimental data. The numerical results reveal that the serration flap angle primarily affects the trailing-edge noise reduction through a modification of: the effective angle at which the turbulent structures are convected over the serrated edge; the convection velocity and spanwise coherence length along the serration; the intensity of the hydrodynamic wall-pressure fluctuations that are scattered along the serrated edge; with the first and last phenomena playing the most significant role on the far-field noise reduction. The best-suited orientation of the add-on in terms of turbulent boundary-layer trailing-edge noise reduction turns out to be that for which the serration is oriented as the mean streamlines deviation angle with respect to the tangent to the mean camber line. Finally, the destructive interference mechanism among noise sources along the serrated edge is found to be largely reduced when a serration is at incidence, compared to zero incidence cases. Then, the prediction of broadband trailing-edge noise, along with that of tonal noise and performances, is extended to a complete propeller geometry operating at low-Reynolds numbers. Specifically, a computational approach based on the use of a zig-zag transition trip applied on the propeller blades is adopted in the numerical simulations to drive the numerical scheme from modeled to scale-resolving turbulence mode, and trigger the formation of vortical structures with scales able to emulate the complexity of a low-Reynolds number boundary-layer on the blade. Two different tripping strategies are attempted by placing the trip along the blade quarter-chord and expected turbulent boundary-layer transition lines, respectively. It is observed that the trip chordwise position marginally affects the thrust prediction and to a slightly larger extent the torque one. Moreover, tonal noise at the blade-passing frequencies results to be insensitive to the trip position, while broadband noise is found to be slightly more influenced by it, especially at high advance ratios at which the boundary-layer transition is expected to occur closer to the blade trailing-edge. Finally, the low sensitivity of the numerical results to the trip location, as well as their good agreement with loads and noise experimental data, demonstrates the robustness of the proposed approach for industrial applications. The same approach is then used to address the impact of angular inflows, due to non-zero propeller angles of attack or yaw angles, on the tonal and broadband noise radiated by a low blade-tip speed propeller. The numerical noise predictions are found to be in a very good agreement with the experimental measurements, with the zig-zag based approach being able to reproduce the strong tonal noise directivity change, as well as the minor variation of the broadband noise levels observed in the experimental data. The numerical results confirmed that the presence of an angular inflow is responsible for a radiation of tonal loading noise along the propeller axis; and for an increment/reduction of the sound pressure level in the region from/to which the propeller is tilted away/towards. However, in contrast to propellers operating at high blade-tip Mach numbers, the noise directivity change is found to be governed only by the rise of periodic unsteady loadings, with the modulation of the strength of the noise sources on the blade - due to the periodic variation of the observer-source relative Mach number (in the rotating frame) - being negligible. Finally, both thickness noise and turbulent boundary-layer trailing-edge noise are not significantly altered when the propeller is yawed with respect to the free-stream. Next, the problem of tonal noise generated by a rotorcraft experiencing strong blade-vortex interaction conditions is considered. The numerical simulations are performed by considering a rigid blade motion, but a computational approach is employed to account for the steady and unsteady aerodynamic effects associated to the blade elastic deformations, through the application of a transpiration velocity boundary condition, a fluid body-force field and the steady deformed blade shape. The predictions of both unsteady loading and far-field noise result to be in a satisfactory agreement with the experimental data, although some intrinsic inaccuracies in the numerical results are observed, primarily due to the lack of a proper simulation of the rotor blade elastic deformations. However, it is shown that the modeling of the aerodynamic effects associated to the elastic deformation of the rotor blade leads to more accurate predictions of trim settings, unsteady airloads and noise footprint. Finally, the lattice-Boltzmann method is applied to the analysis of the noise generation mechanisms and to the quantification of the related tonal and broadband noise emissions of a boundary-layer ingesting ducted-fan/OGV (outlet guide vane) embedded propulsion system. The analysis is performed by considering a modified version of the Low-Noise NASA SDT fan-stage integrated into the ONERA NOVA fuselage. Installation effects due to the boundary-layer ingestion are quantified by comparison with an isolated configuration of the modified Low-Noise SDT fan-stage at the same operating condition, namely a take-off with power cut-back. It is found that the boundary-layer ingesting fan/OGV stage is characterized by strong azimuthal fan blade loading unsteadiness, less axisymmetric and coherent rotor wake tangential velocity variations and higher levels of in-plane velocity fluctuations compared to the isolated engine. This results in no distinct tonal components and higher broadband levels up to 20 dB in the far-field noise spectra, as well as in an increment of the cumulative noise levels up to 18 EPNdB.
... Once carbon dioxide is emitted, it can remain in the atmosphere for centuries. In addition, another significant aviation emission class, NO X emissions, increase tropospheric ozone concentration when emitted at high altitudes, thus warming the atmosphere [8]. Aerosol soot can eventually settle on arctic regions. ...
... This settling blackens the low albedo surface, alone causing an estimate of 25% of global warming [9]. The total global warming contribution of the aviation industry is predicted to be about 5% [8], highlighting the need to hasten improvement in low/no emission technologies. ...
Article
Full-text available
A theory-based aerodynamic model developed and applied to electrified powertrain configurations was intended to analyze the feasibility of implementing fully electric and serial hybrid electric propulsion in light-sport aircraft. The range was selected as the primary indicator of feasibility. A MATLAB/Simulink environment was utilized to create the models, involving the combination of proportional-integral-derivative controllers, aerodynamic properties of a reference aircraft, and powertrain limitations taken from off-the-shelf components. Simulations conducted by varying missions, batteries, fuel mass, and energy distribution methods provided results showcasing the feasibility of electrified propulsion with current technology. Results showed that the fully electric aircraft range was only 5% of a traditionally powered aircraft with current battery technology. Hybrid electric aircraft could achieve 44% of the range of a traditionally powered aircraft, but this result was found to be almost wholly related to fuel mass. Hybrid electric powertrains utilizing an energy distribution with their optimal degree of hybridization can achieve ranges up to 3% more than the same powertrain utilizing a different energy distribution. Results suggest that improvements in the power-to-weight ratio of the existing battery technology are required before electrified propulsion becomes a contender in the light-sport aircraft segment.
... Especially since the growth of air transport, noise reduction technologies and their environmental impact are of great importance. Various authors have already shown that worldwide air traffic plays an important role in environmental pollution [5][6][7]. The aviation sector's CO 2 contribution is estimated at 2.5% of the anthropogenic CO 2 emission worldwide [8]. ...
... Mission profile for the design mission, including: departure (1), cruise (2), approach (3), diversion (4), loiter(5). ...
Article
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Promising low-noise aircraft architectures have been identified over the last few years at DLR. A set of DLR aircraft concepts was selected for further assessment in the context of sustainable and energy-efficient aviation and was established at the TU Braunschweig in 2019, the Cluster of Excellence for Sustainable and Energy-Efficient Aviation (SE2A). Specific Top-Level aircraft requirements were defined by the cluster and the selected DLR aircraft designs were improved with focus on aircraft noise, emissions, and contrail generation. The presented paper specifically addresses the reduction of aviation noise with focus on noise shielding and modifications to the flight performance. This article presents the state of the art of the simulation process at DLR and demonstrates that the novel aircraft concepts can reduce the noise impact by up to 50% in terms of sound exposure level isocontour area while reducing the fuel burn by 6%, respective to a conventional aircraft for the same mission. The study shows that a tube-wing architecture with a top-mounted, forward-swept wing and low fan pressure ratio propulsors installed above the fuselage at the wing junction can yield significant noise shielding at improved low-speed performance and reduce critical fuel burn and emissions,
... [1]. Entsprechend ist auch nach dem aktuell nahezu weltweiten Erliegen des Luftverkehrs durch den Coronavirus SARS-CoV-2 davon auszugehen, dass nach Überstehen der Pandemie die Luftfahrt zukünftig wieder Wachstum erfährt und, wie schon in den vergangenen Jahren, immer größeren ökologischen sowie ökonomischen Herausforderungen gegenübersteht [2]. Gerade der zunehmende Druck durch eine aggressive Preiswirtschaft, neue gesetzliche Vorgaben und CO 2 [4]. ...
... Entsprechend ist auch nach dem aktuell nahezu weltweiten Erliegen des Luftverkehrs durch den Coronavirus SARS-CoV-2 davon auszugehen, dass nach Überstehen der Pandemie die Luftfahrt zukünftig wieder Wachstum erfährt und, wie schon in den vergangenen Jahren, immer größeren ökologischen sowie ökonomischen Herausforderungen gegenübersteht [2]. Gerade der zunehmende Druck durch eine aggressive Preiswirtschaft, neue gesetzliche Vorgaben und CO 2 [4]. Der Einsatz der duroplastischen Faserverbundkunststoffe erfolgt aufgrund der hohen Verarbeitungskosten und eingeschränkten Verarbeitungsverfahren jedoch bisher primär an geometrisch einfachen Komponenten der Primärstruktur wie Rumpf und Flügeln oder den Außenverkleidungen der Turbinen [4]. ...
Thesis
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Vorimprägnierte flächige Halbzeuge auf Basis endlosfaserverstärkter Duroplaste bieten durch ihre vorteilhaften gewichtsbezogenen Eigenschaften und die spezifischen Eigenschaften ihrer Matrix, wie z. B. Temperaturbeständigkeit oder Notlaufeigenschaften, ein großes Potenzial für Leichtbau in anspruchsvollen Anwendungsgebieten wie der Luftfahrt. Aufgrund des zunehmenden Bedarfs einer zeitgleichen Funktionalisierung oder Erhöhung der Geometriekomplexität von solchen Komponenten sind vor allem integrative Fertigungsverfahren als Schlüssel zur effizienten und wirtschaftlichen Fertigung zu sehen. Durch die integrative Fertigung werden unterschiedliche Werkstoffe mit differenzierten spezifischen Eigenschaften in einem Prozessschritt kombiniert und als ein Bauteil bzw. Hybridbauteil entformt. Die große Schwachstelle eines solchen Hybridbauteils bildet jedoch die Grenzfläche zwischen den kombinierten Werkstoffen. Damit hängt der Erfolg eines integrativen Fertigungsverfahrens für Duroplaste maßgeblich von der Realisierung einer belastbaren Grenzfläche ab, wobei die Werkstoffeigenschaften der Einzelkomponenten nicht geschwächt werden dürfen. Im Rahmen dieser Arbeit wird eine neuartige Methodik zur integrativen Kombination von duroplastischen Formmassen und duroplastischen Prepregs im unvernetzten Zustand mittels Duroplast- Spritzgießverfahren aufgezeigt. Neben der charakteristischen Grenzflächenentstehung werden die Zusammenhänge zwischen dominierenden Prozesseinflüssen und resultierenden Bauteileigenschaften identifiziert sowie zugrundeliegende Ursachen beleuchtet. Hierfür werden sowohl ausgewählte werkstoffliche als auch prozesstechnische Parameter in Labor- und Verarbeitungsversuchen variiert, analysiert und verknüpft. Zudem werden dominierende Adhäsionsmechanismen und zugehörige charakteristische Versagensverhalten analytisch beschrieben und evaluiert. Auf Basis der Ergebnisse werden Richtlinien für ein stabiles Prozessfenster und Empfehlungen für die Bauteilauslegung des neuartigen integrativen Verfahrens abgeleitet. Diese bilden einen weitreichenden Beitrag für eine potenzielle Weiterentwicklung des Verfahrens bis hin zu Serienreife.
... It is estimated that the aviation sector is developing at an annual rate of 5% [1,2] and contributes to 5% of the net radiative forcing of climate [3] and 2.6% of global anthropogenic CO 2 emissions [4], which is predicted to reach 5% by the year 2050 [5]. ...
... As mentioned earlier, the LHVs of alternative fuels are smaller than that of kerosene. Hence, according to formula (3), in order to maintain the same temperature value in front of the turbine (T 3 *), more fuel must be supplied to the combustion chamber. ...
Article
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Due to environmental pressure and the prevailing political and economic situation in the world, alternatives to traditional fossil fuels are being sought. The use of bio-derived fuels may reduce the emission of pollutants present in jet engine exhausts. The presented research investigates the possibility of replacing the conventional fuel, which is kerosene, with plant-derived fuels from marine algae and jatropha. During the analysis, based on the available data, the emission indices of pollutants were computed, and then, for the adopted aircraft and route, the emissions for kerosene and alternative fuels were determined. A significant reduction in the emission of most analyzed compounds (even by 40% for CO) was achieved compared to the emission for kerosene. The obtained results are discussed in the conclusion section.
... Estimates of the current contribution of global aviation to total anthropogenic CO 2 emissions are between 2% to 2.5% (IPCC, 1999, IPCC, 2007, Lee et al., 2009. International aviation accounts for approximately 65% of total aviation emissions or 1.3% of all anthropogenic CO 2 emissions (ICAO, 2016). ...
... In addition to this, the sector further contributes to global warming with its non-CO 2 emissions, which are estimated to have a radiative forcing 1 effect at least equal to that of its CO 2 emissions (Cames et al., 2015). In fact, estimates of climate impacts of all direct and indirect GHG emissions of global aviation expressed as radiative forcing indicate a more substantial current contribution of the sector at almost 5% of anthropogenic warming (Lee et al., 2009). However, aviation non-CO 2 emissions are still subject to significant uncertainty. ...
Technical Report
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This study aims to provide a realistic assessment of the biofuel production potential of countries in sub-Saharan Africa, based on latest available information, and conforming to strict sustainability criteria considering the region’s food and environmental safeguard requirements, as well as GHG LCA results of biofuels from alternative feedstocks that could potentially be produced here. The sustainability constraints have been operationalised following the criteria of the Roundtable for Sustainable Biomaterials, which is considered best-in-class in terms of sustainability standards for bioenergy developments (WWF, 2013). The goal is therefore to estimate current and future sustainable biofuel potentials for sub-Saharan Africa (SSA) in accordance with the principles of the Roundtable on Sustainable Biomaterials (RSB), in light of demand from land-based transportation and aviation. The study objectives include: • Examine the RSB principles and criteria for implementation in the analysis • Use future scenarios up to 2050 for the assessment of future food demand and associated land and water requirements • Compile geospatial land and water resources databases for sub-Saharan Africa
... Another major emission class from aircraft, NOX emissions, generally appear in the public discourse in relation to their adverse health effects. On the other hand, when emitted at high altitudes, they are also known to increase the concentration of the tropospheric ozone leading to a warming of the atmosphere [8]. Another major aircraft emission is particulate matter, which also influences the energy balance of our planet. ...
... Aerosol soot settles on arctic regions and darkens the low albedo surface, which is suspected to be responsible alone for a quarter of the global warming [9]. It is estimated that the total contribution of the aviation industry to global warming is about 5% [8]. Therefore, there is an urgent need to fast-track development in low/no emission technologies. ...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-2050.vid A theory-based aerodynamic model was developed and applied to electrified powertrain configurations to study the feasibility of implementing fully electric and hybrid electric technologies into light sports aircraft. Overall aircraft range was chosen as the main indicator of feasibility. The aerodynamic models were created in MATLAB/Simulink utilizing proportional-integral-derivative controllers, aerodynamic specifications of a reference aircraft body, and powertrain limitations from a physical electrified powertrain test stand. Simulations that were conducted by varying mission properties, battery properties, and fuel mass provide results which can showcase the current feasibility of electrified propulsion and make predictions for the future of the industry. Results showed that aircraft powered with a fully electric powertrain were only able to achieve 5% of the range of a traditionally powered aircraft. Aircraft using a hybrid electric powertrain were able to achieve 44% of the range of a traditionally powered aircraft, but this result was found to be almost entirely dependent on the aircraft’s fuel mass. Future predictions of Lithium-Ion battery technology are expected to increase range of fully electric aircraft to 25% of traditional, and hybrid aircraft to 60% of traditional.
... All available liquid biofuels in India are likely to be used up in sectors that are hard to decarbonize in any other way. Globally, the aviation sector alone could use three to four times more fuel in 2050 as it did in year 2000 if it resumes its pre-pandemic growth rate, resulting in an estimated 766 million tonnes of fuel burned or 32 EJ per year [23,24]. ...
Article
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By considering the weight penalty of batteries on payload and total vehicle weight, this paper shows that almost all forms of land-based transport may be served by battery electric vehicles (BEV) with acceptable cost and driving range. Only long-distance road freight is unsuitable for battery electrification. The paper models the future Indian electricity grid supplied entirely by low-carbon forms of generation to quantify the additional solar PV power required to supply energy for transport. Hydrogen produced by water electrolysis for use as a fuel for road freight provides an inter-seasonal energy store that accommodates variations in renewable energy supply. The advantages and disadvantages are considered of midday electric vehicle charging vs. overnight charging considering the temporal variations in supply of renewable energy and demand for transport services. There appears to be little to choose between these two options in terms of total system costs. The result is an energy scenario for decarbonized surface transport in India, based on renewable energy, that is possible, realistically achievable, and affordable in a time frame of year 2050.
... Air traffic provides a significant contribution to anthropogenic global warming. In 2005, aviation contributed about 5% of the overall anthropogenic radiative forcing (RF), with the largest warming contributions being due to CO 2 emissions, contrail cirrus formation, and NO X net effects [1]. It is possible to reduce the environmental impact of aviation by intervening at the Air Traffic Management (ATM) level. ...
Article
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Aviation contribution to global warming and anthropogenic climate change is increasing every year. To reverse this trend, it is crucial to identify greener alternatives to current aviation technologies and paradigms. Research in aircraft operations can provide a swift response to new environmental requirements, being easier to exploit on current fleets. This paper presents the development of a multi-objective and multi-phase 4D trajectory optimization tool to be integrated within a Flight Management System of a commercial aircraft capable of performing 4D trajectory tracking in a Free Route Airspace context. The optimization algorithm is based on a Chebyshev pseudospectral method, adapted to perform a multi-objective optimization with the two objectives being the Direct Operating Cost and the climate cost of a climb-cruise-descent trajectory. The climate cost function applies the Global Warming Potential metric to derive a comprehensive cost index that includes the climate forcing produced by CO2 and non-CO2 emissions, and by the formation of aircraft-induced clouds. The output of the optimization tool is a set of Pareto-optimal 4D trajectories among which the aircraft operator can choose the best solution that satisfies both its economic and environmental goals.
... Among the proposed approaches to mitigate aircrafts' impacts such as the optimization of the aerodynamics, flight management, and the use of biofuels, reducing the aircraft's weight has already had successful outcomes [4]. This weight reduction has been allowed mostly by replacing metallic parts with composite materials such as carbon fiber reinforced polymers (CFRPs) or hybrid glass aluminum reinforced epoxy laminates (GLARE) [5], and has been reported to decrease the overall environmental impact of aircrafts during their flight [2,6,7]. ...
Preprint
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Aviation's fossil fuel emissions contribute to global warming. The production and disposal of the materials used in aircrafts too. The current metallic alloys present in the hot section of engines pose constraints in terms of temperature, pressure and weight that restrain the performance of the aircrafts. Also, these alloys are produced using rare, depleting resources, and polluting processes. In this paper, we hypothesize the use of bioinspired nacre-like alumina (NLA), a ceramic material that exhibits unusual toughness, and evaluate its potential as a replacement for superalloys in aircraft's engines. Comparing the performance of Ni superalloys and NLA in terms of properties, engine performance, and life cycle sustainability, we find NLA a promising alternative although progress has to be made with regards to its reliability, shaping, repair, and governance of the production process.
... The results discussed in the previous section do not include two components of radiative forcing which are significant for subsonic aviation-CO 2 and aviationinduced cirrus ("contrails") (Lee et al., 2009). For CO 2 , the calculation of radiative forcing requires consideration of timescale (Kawa et al., 1999). ...
Technical Report
We analyze the climate and ozone impacts of commercial supersonic aircraft using state-of-the-science modeling capabilities ranging from plume to global scale. A scenario-based approach captures variability and uncertainty in the impacts with market adoption, aircraft design choices and regulatory scenarios, focusing on different overland flight restrictions. We find that the notional aircraft considered could attract a market of up to 2.5% of year-2035 seat-kilometers. Overland flight restrictions reduce this market by 80–100%. In comparison to subsonic aircraft, contrails are found to be ∼ 10 times less likely to form behind supersonic jets. A Mach 1.6 jet cruising at 17 km altitude causes 0.85 mDU of depletion per billion seat-km, with 54% of this impact attributable to sulfur emissions and 35% to NOx emissions. As a result, we find a net non-CO2, non-contrail radiative forcing of −0.020mWm−2 per billion seat-km. Long-term adjoint simulations show that net ozone-neutral cruise can be achieved by flying near 14 km, subject to fuel sulfur content and NOx emissions index. The full text can be found in https://ntrs.nasa.gov/citations/20205009400.
... Therefore, establishing sensitivities can be a particularly valuable approach [47]. Multi-model evaluations have also proven to be valuable in avoiding these shortcomings in the case of subsonic aviation [7,88,89], as well as for the case of supersonic aviation [9]. ...
Article
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When working towards regulation of supersonic aviation, a comprehensive understanding of the global climate effect of supersonic aviation is required in order to develop future regulatory issues. Such research requires a comprehensive overview of existing scientific literature having explored the climate effect of aviation. This review article provides an overview on earlier studies assessing the climate effects of supersonic aviation, comprising non-CO2 effects. An overview on the historical evaluation of research focussing on supersonic aviation and its environmental impacts is provided, followed by an overview on concepts explored and construction of emission inventories. Quantitative estimates provided for individual effects are presented and compared. Subsequently, regulatory issues related to supersonic transport are summarised. Finally, requirements for future studies, e.g., in emission scenario construction or numerical modelling of climate effects, are summarised and main conclusions discussed.
... Model parameter estimates for the CCD phase are presented in Table 4. Insignificant parameter estimates may be due to the fact that estimating CO, HC and other atmospherically processed emissions not included in this study such as CH 4 and cirrus clouds have always presented challenges, mainly because these emissions depend on operational and ambient conditions more than on volume of aviation fuel burned (Scheelhaase, et al., 2016;Fuglestvedt, et al., 2010;Lee, et al., 2009). Nonetheless, such insignificant model parameters have been used to estimate average aviation fuel consumption/ pollutant emissions in the past (Cox et al., 2018) and we also use them in this study. ...
Article
Attractive air services at large airports in the U.S., over the last two decades, have encouraged interregional air passenger leakage, a phenomenon in which air travelers abandon their nearby small airports in favor of starting their air journeys from large hub airports farther away. The disparities between small and large airports, in terms of air services, are expected to widen because of COVID-19 and further exacerbate passenger leakage. This study estimates the differences in mean aviation fuel consumed and pollutants emitted between air routes from small and large airports in the U.S. Midwest region – routes that are known to be contested according to analysis of an air ticket dataset. Findings indicate that air journeys originating from large airports result in 24% less aviation fuel consumption and considerably lower emissions at the passenger-kilometer level, offering additional insight toward better understanding the environmental impact of a geographically shifting air travel demand.
... Lee et al. (2021) give best estimates with 90 % uncertainty ranges (from the 5 % -95 % confidence intervals), of which the non -CO2 ERF terms contribute about 8 times more to the uncertainty of aviation net ERF than the CO2. Older estimates for contrail cirrus RF for 2011 (Boucher et al., 2013) and for aviation-induced cloudiness (which includes contrail cirrus) for 2005 (Lee et al., 2009) (2011), Chen and Gettelman (2013) and Schumann et al. (2015a). ...
Thesis
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Persistent contrails and contrail cirrus are estimated to have a larger climate impact than all CO2 emissions from global aviation since the introduction of jet engines. However, the measure for this impact, the radiative forcing (RF) or effective radiative forcing (ERF) comes with much larger uncertainties than those for CO2. This study investigates one of the major causes for uncertainty, the natural variability. Specifically, the weather-induced variability is examined from a large dataset of instantaneous radiative forcing (iRF) values, produced from ten years of MOZAIC flights and ERA-5 reanalysis data. Cdfs and pdfs of the iRF dataset show strong annual and interannual variations and a seasonal pattern. 80% of the contrails have a small positive iRF of up to 20 Wm-2, 10% of all cases have an iRF ≥ 19 Wm-2, but these have a disproportionally large climate impact, and the remaining 10% have negative iRF. The distribution of iRF values declines exponentially at positive values and is heavily skewed. Monte Carlo experiments reveal the difficulty of determining a precise long-term mean from measurement campaign data. Depending on the chosen sample size, calculated means scatter considerably, which is caused exclusively by weather variability. This variability is the lower limit for uncertainty, which suggests, that there is a fundamental limit to the precision with which the RF and ERF of contrail cirrus can be determined. The accurate local prediction of persistent contrails is still not possible because of errors in the humidity field in most weather prediction models. When the meteorological and dynamical conditions of persistent contrails and Big Hits (the strongest warming contrails) are known, they could be used as an addition to the SAC quantities to improve prediction possibilities. The data showed, that Big Hits favor small negative vertical velocities, small positive divergence, anticyclonic flow, low potential vorticities up to 4 PVU, large geopotential heights, and large lapse rates up to 10 K km-1. The last four variables showed the strongest separation of the pdf´s and are best suited for improving the prediction of persistent contrails. This was tested with a logistic regression model and with model output statistics for conditional probabilities. The results showed, that, 1) predicting Big Hits is quite reliable when it is already known that contrails will be persistent and 2) high probabilities for the persistence of contrails can be determined by introducing thresholds for dynamical variables and combining them with the SAC quantities. When such thresholds could be included in a weather prediction model like ECMWF´s integrated forecast model (IFS), probabilities for contrail persistence could be produced before the flight planning period. Avoidance of persistent contrails or Big Hits would then become more reliable.
... Aircraft engines produce power by burning fuel and create oxidised outputs called emissions as carbon dioxide (CO 2 ), nitrogen oxide (NO X ), sulphur oxide (SO X ), carbon monoxide (CO), water vapour (H 2 O), and hydrocarbons (HC). Mentioned emissions have a notable impact on the atmosphere by soaring greenhouse gases (GHG), forming the particles on condensational trails, and curling the air to create cirrus clouds (Lee et al., 2009(Lee et al., , 2010. Human and nature effects of mentioned emissions of aircraft engines near the airport just below the mixing height (3,000 feet or 914 metres above the runway of airport) modes a public opinion on its behalf (Liu et al., 2017;Yilmaz, 2017). ...
Article
This study presents an environmental damage analysis of GE90 engine series for takeoff , climb-out, approaching and cruise phases to evaluate the emission rates, the global warming potentials (GWP), the global warming potential index (GWPI), the environmental impact (EI), the environmental impact index (EII), the environmental damage cost (EDC) and the environmental damage cost index of exhaust gases emitted from GE90 turbofan engines via standard dual annular combustor (SDAC) and low emission dual annular combustor (LEDAC). The GE90-76B engine has the maximum exhaust emission rate by 3.694 kg/h for SDAC usage. The GE90-92B engine has the maximum NOX emission rate by 755.40 kg/h for SDAC usage and 707.40 kg/h for LEDAC usage. The results can be used by airlines, countries, or companies that use GE90 engine series.
... Previous assessments of global aviation climate have made different assumptions regarding aviation emissions and aviation operations. The understanding of the effects of aviation on climate has been improved in the past decade but is still incomplete [25], as the challenges linked to the reduction in GHG emissions from the aviation industry are very diverse [26]. In recent years, not enough significant research work has been carried out regarding the contribution of aircraft emissions from the EU and the UK in the increasing global warming trend. ...
Article
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There has been a continuously growing trend in international commercial air traffic, with the exception of COVID-19 crises; however, after the recovery, the trend is expected to even sharpen. The consequences of released emissions and by-products in the environment range from human health hazards, low air quality and global warming. This study is aimed to investigate the role of aviation emissions in global warming. For this purpose, data on different variables including global air traffic and growth rate, air traffic in different continents, total global CO 2 emissions of different airlines, direct and indirect emissions, air traffic in various UK airports and fuel-efficient aircraft was collected from various sources like EU member states, Statista, Eurostat, IATA, CAA and EUROCONTROL. The results indicated that in 2019, commercial airlines carried over 4.5 × 10 ⁹ passengers on scheduled flights. However, due to the COVID-19 pandemic in 2020, the global number of passengers was reduced to 1.8 × 10 ⁹ , representing around a 60% reduction in air traffic. Germany was the largest contributor to greenhouse gas (GHG) from the EU, releasing 927 kt of emissions in 3 years. In the UK, Heathrow airport had the highest number of passengers in 2019 with over 80 million, and the study of monthly aircraft movement revealed that Heathrow Airport also had the highest number of EU and International flights, while Edinburgh had the domestic flights in 2018. These research findings could be beneficial for airlines, policymakers and governments targeting the reduction of aircraft emissions. Graphical abstract
... Lee et al. [1] give best estimates and 90% uncertainty ranges (5-95% confidence intervals) for the components of aviation ERF. For CO 2 these values are 34.3 (28,40) [2] for "aviation induced cloudiness" (which includes contrail cirrus) that gives 33 (11,87) mW m −2 , quite considerably lower than the new estimate, but still the uncertainty bars overlap. ...
Article
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Citation: Wilhelm, L.; Gierens, K.; Rohs, S. Weather Variability Induced Uncertainty of Contrail Radiative Forcing. Aerospace 2021, 8, 332. Abstract: Persistent contrails and contrail cirrus are estimated to have a larger impact on climate than all CO 2 emissions from global aviation since the introduction of jet engines. However, the measure for this impact, the effective radiative forcing (ERF) or radiative forcing (RF), suffers from uncertainties that are much larger than those for CO 2. Despite ongoing research, the so called level of scientific understanding has not improved since the 1999 IPCC Special Report on Aviation and the Global Atmosphere. In this paper, the role of weather variability as a major component of the uncertainty range of contrail cirrus RF is examined. Using 10 years of MOZAIC flights and ERA-5 reanalysis data, we show that natural weather variability causes large variations in the instantaneous radiative forcing (iRF) of persistent contrails, which is a major source for uncertainty. Most contrails (about 80%) have a small positive iRF of up to 20 W m −2. IRF exceeds 20 W m −2 in about 10% of all cases but these have a disproportionally large climate impact, the remaining 10% have a negative iRF. The distribution of iRF values is heavily skewed towards large positive values that show an exponential decay. Monte Carlo experiments reveal the difficulty of determining a precise long-term mean from measurement or campaign data alone. Depending on the chosen sample size, calculated means scatter considerably, which is caused exclusively by weather variability. Considering that many additional natural sources of variation have been deliberately neglected in the present examination, the results suggest that there is a fundamental limit to the precision with which the RF and ERF of contrail cirrus can be determined. In our opinion, this does not imply a low level of scientific understanding; rather the scientific understanding of contrails and contrail cirrus has grown considerably over recent decades. Only the determination of global and annual mean RF and ERF values is still difficult and will probably be so for the coming decades, if not forever. The little precise knowledge of the RF and ERF values is, therefore, no argument to postpone actions to mitigate contrail's warming impact.
... It is estimated that the CO 2 emissions generated by aviation are 2.5-3% of the anthropogenic CO 2 , causing 5-9% of the anthropogenic radiative forcing (Lee et al., 2009). To address this, the EU has signed in 2020 The European Green Deal Investment Plan (Tamma et al., 2020), which aims to achieve a climate neutral EU by 2050 by investing in environmentally-friendly technologies, and rolling out cleaner, cheaper and healthier forms of private and public transport. ...
Article
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With the current advances in aircraft design and Lithium-Ion batteries, electric aircraft are expected to serve as a replacement for conventional, short-range aircraft. This paper addresses the main operational challenges for short-range flights operated with electric aircraft: determining the investment needs for a fleet of electric aircraft, and the logistics of charging stations and swap batteries required to support these flights. A mixed-integer linear program with two phases is proposed. In the first phase, a schedule for flight and battery recharge is developed for a fleet of electric aircraft. In the second phase, optimal times for battery charging are determined, together with an optimal sizing of the number of charging stations and swap batteries. We illustrate our model for short-range flights to and from an European airport and for an electric aircraft designed based on the operational characteristics of a conventional, narrow-body aircraft.
... Finally, in contrast to CORSIA, the tax and market combination would lead to direct emission reductions in the aviation sector instead of relying on carbon credits from occasionally questionable projects. 25 The impacts may increase up to 40%, without including aviation-induced clouds that may lead up to a doubling of impacts (Lee et al, 2009;Azar and Johansson, 2012). 26 These reforms should also contemplate taxing air freight so that all the externalities caused by air transport are addressed and inefficient tax treatments avoided. ...
Article
The importance of energy-environmental taxation in the transition to decarbonized economies does not correspond to its actual role due to several constraints on its application. This paper emphasizes one of the main barriers, the negative impacts on distribution and equity, and suggests alternatives to mitigate these effects. In particular, it lists a series of fiscal proposals for road transport and aviation, sources of significant emissions, defined and empirically evaluated for the specific case of Spain, with compensatory packages to reduce their regressive nature and thus support their viability in practice.
... This radiative imbalance is referred to as radiative forcing (RF). The overall global aviation RF of non-CO 2 effects is positive and thus warming [3]. Moreover, it is important to note that non-CO 2 emissions are responsible for two-thirds of the global aviation RF [1,4]. ...
Article
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The strong growth rate of the aviation industry in recent years has created significant challenges in terms of environmental impact. Air traffic contributes to climate change through the emission of carbon dioxide (CO2) and other non-CO2 effects, and the associated climate impact is expected to soar further. The mitigation of CO2 contributions to the net climate impact can be achieved using novel propulsion, jet fuels, and continuous improvements of aircraft efficiency, whose solutions lack in immediacy. On the other hand, the climate impact associated with non- CO2 emissions, being responsible for two-thirds of aviation radiative forcing, varies highly with geographic location, altitude, and time of the emission. Consequently, these effects can be reduced by planning proper climate-aware trajectories. To investigate these possibilities, this paper presents a survey on operational strategies proposed in the literature to mitigate aviation’s climate impact. These approaches are classified based on their methodology, climate metrics, reliability, and applicability. Drawing upon this analysis, future lines of research on this topic are delineated.
... In recent years, the aerospace industry has been directed towards reducing the emissions and carbon footprint, additionally, increasing the fuel economy and safety of the aerostructures to be more economical and more competitive (Braga et al. 2014). Emissions of the aerospace industry have multiplied nearly two times in the last twenty years, with the industry accounting for 4.9% share of the total emissions worldwide that contribute to climate change (Lee et al. 2009). Advanced methods such as weight reduction with complex designs have significantly improved the performance of the aerospace industry products, decreased the environmental effects, as well as launching costs (a launch service to geosynchronous orbit (GEO) costs nearly $13,000/kg) (Koelle 2003;Weigel and Hastings 2004). ...
Article
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In the aerospace industry, structures are designed (or aimed) to be as light as possible to reduce emissions and carbon footprint; additionally, they are designed to improve fuel efficiency and service life while satisfying the mechanical requirements. Due to the development of additive manufacturing technology, complex structures with higher mechanical performance obtained through topology optimization (TO) can be manufactured. In this study, the overall process from part selection to qualification for a space industry-engineering application is described. First, the design space of the selected aluminum bracket is generated, and TO is performed by using stress and minimum member size constraints. The bracket is re-designed with respect to the TO output data as a reference and then the new design is validated numerically by structural analyses. The validated design is manufactured using the selective laser melting method, and heat treatment is applied to obtain more homogenized microstructure. Mechanical tests are performed on the manufactured brackets under the qualification loading conditions and post-testing examination processes are applied with metallurgical and metrological tests. According to the test results, the qualification process of the bracket is successfully completed. Consequently, the new bracket designed with TO was found to be 25% lighter than the existing design; thus, it has a huge improvement in fuel efficiency and environmental impact during the launching phase.
... Nitrogen oxides react in the atmosphere altering the radiative balance of other gases, including methane (CH 4 ), ozone (O 3 ) and stratospheric water vapour (H 2 O) and therefore indirectly impact the climate. These non-CO 2 emissions cause an additional net warming effect (Lee et al 2009). ...
Article
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Growth in aviation contributes more to global warming than is generally appreciated because of the mix of climate pollutants it generates. Here, we model the CO 2 and non-CO 2 effects like nitrogen oxide emissions and contrail formation to analyse aviation’s total warming footprint. Aviation contributed approximately 4% to observed human-induced global warming to date, despite being responsible for only 2.4% of global annual emissions of CO 2 . Aviation is projected to cause a total of about 0.1 °C of warming by 2050, half of it to date and the other half over the next three decades, should aviation’s pre-COVID growth resume. The industry would then contribute a 6%–17% share to the remaining 0.3 °C–0.8 °C to not exceed 1.5 °C–2 °C of global warming. Under this scenario, the reduction due to COVID-19 to date is small and is projected to only delay aviation’s warming contribution by about five years. But the leveraging impact of growth also represents an opportunity: aviation’s contribution to further warming would be immediately halted by either a sustained annual 2.5% decrease in air traffic under the existing fuel mix, or a transition to a 90% carbon-neutral fuel mix by 2050.
... Emissions from flights in high-altitude airspace can accelerate changes in atmospheric chemistry and micro-particle physics, and have an amplifying effect on climate change [17], which is one of the key issues concerning "green civil aviation". Moreover, the cruise phase accounts for 80% of the flight time, and most fuel consumption and pollutant emissions occur in this phase. ...
Article
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In order to improve the capability of situational awareness and operational efficiency by considering environmental impact, a prediction model for short-term flight emissions within en route airspace is proposed in this paper. First, the measurement method of fuel consumption and flight emissions based on actual meteorological data is established, and the pattern of flight emissions is analyzed. Then, an adaptive weighting approach is proposed by considering prediction results obtained from a long–short term memory (LSTM) prediction model and extreme gradient boosting (XGBoost) prediction model, respectively. Taking the Guangzhou area control centre (ACC) AR05 sector in central and southern China as an example, the model is trained and tested on emission datasets with three statistical scales, 60 min, 30 min, and 15 min. The result shows that the combined variable–weight prediction model has the greatest prediction effect compared to six other models. In terms of time scale, the prediction performance is best on the 60 min statistical scale dataset; larger statistical unit magnitudes of emissions during the predicting process show better short-term prediction performance. In addition, the increase in data features when training the model plays an essential role in promoting model accuracy. The model established in this paper has high prediction accuracy and stability, which is capable of providing short-term prediction of airspace flight emissions.
... It is noted that in-flight fuel combustion emissions in this work are modeled like near-ground CO 2 emissions. It is well known that aviation affects the climate through additional mechanisms, e.g. by emitting NOx, soot, and water into the upper troposphere and lower stratosphere [31][32][33]. However, quantifying these effects is beyond the scope of this work. ...
Conference Paper
The overarching goal in the GNOSIS project is to holistically evaluate the potential through aircraft propulsion system electrification at the two temporal assessment horizons in 2025 and 2050. In this context, one of the evaluation parameters is the CO2 equivalent emissions associated with aircraft operations. In this study, the aforementioned emissions are calculated for two electrified aircraft configurations with 19 seats passenger capacity, determined in previous project phases. Afterwards, the emissions are compared to those of the aircraft operated either with conventional kerosene or sustainable aviation fuels from different production pathways. In order to achieve the set goal, two main steps are carried out. First, the MICADO framework for aircraft design and evaluation is extended with new models for the required propulsion system components. Second, based on a literature review, the CO2 equivalent well-to-wheel emissions associated with production and combustion per kilogram of fuel are determined for kerosene, grid electricity and three sustainable aviation fuels. Results show that the partial turboelectric propulsion system selected for 2025 increases the overall system complexity significantly without providing noteworthy advantages over a conventionally powered reference configuration. At the same time, the great potential of SAF becomes apparent if an efficient production path is chosen. According to the results for the year 2050, the use of fossil kerosene for 19-seat passenger aircraft should be dispensed with. The kerosene alternatives investigated here, i.e. combusting 100% SAF in gas turbines or using liquid hydrogen in fuel cells, reduce the equivalent CO2 emissions associated with the production and combustion of the fuels significantly. Savings range between 45 to 80% depending on the main source of energy.
... Die Unsicherheiten wurden aus Sensitivitäten der Prozesse und den Unsicherheiten der zugrundeliegenden Parameter abgeleitet (Yang et al., 2010 Um das Reduktionspotential der Strahlungsantriebe von Kondensstreifenzirren und luftverkehrinduzierten Kohlendioxidemissionen vergleichen zu können, ist auch eine Betrachtung der Lebensdauern beider Komponenten ausschlaggebend. Während Kondensstreifenzirren nur einige Stunden existieren und dann vollständig sublimieren, können Kohlendioxidmoleküle Jahrtausende in der Atmosphäre verbleiben (Archer et al., 2009;Lee et al., 2009 Einen geringen positiven Strahlungsantrieb hat auch Wasserdampf, der in der normalerweise trockenen Stratosphäre emittiert wird. Dort wirkt Wasserdampf als Treibhausgas und trägt zum Abbau von Ozon bei (Gauss et al., 2003). ...
Thesis
Kondensstreifen haben durch Absorption und Reemittierung von langwelliger terrestrischer Strahlung den größten Beitrag am luftverkehrsbedingten Strahlungsantrieb. Ihre Lebensdauer beträgt nur wenige Stunden und daher wirken sich Änderungen der Kondensstreifeneigenschaften schnell und unmittelbar auf ¨den Klimaeffekt des Luftverkehrs aus. Emittiertes Kohlendioxid kann dagegen Jahrtausende in der Atmosphäre verbleiben und dort als Treibhausgas wirken. Die vorliegende Arbeit untersucht, ob und in welchem Umfang die Eigenschaften von Kondensstreifen durch den Einsatz von aromatenarmen Treibstoffen verändert werden kann. Zu diesem Zweck fand im Januar 2018 die Flugzeugmission Emissions and Climate Impact of Alternative Fuels II (ECLIF II) statt.
... Burkhardt and Kärcher [168] summarise the parametrisations necessary to include contrail radiative forcing in global models; this includes parametrising the factors affecting ice supersaturation, contrail formation and persistence, contrail spreading and ice water content. This led to the development of the process-based contrail cirrus module (CCMod), which was later implemented in the global climate model ECHAM4, for global contrail cirrus radiative forcing analysis [105,170,171]. More recently, a microphysical extension to CCMod was applied and implemented in ECHAM5 [159,172]. ...
Article
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Non-CO2 aircraft emissions are responsible for the majority of aviation’s climate impact, however their precise effect is largely dependent on the environmental conditions of the ambient air in which they are released. Investigating the principal causes of this spatio-temporal sensitivity can bolster understanding of aviation-induced climate change, as well as offer potential mitigation solutions that can be implemented in the interim to low carbon flight regimes. This review paper covers the generation of emissions and their characteristic dispersion, air traffic distribution, local and global climate impact, and operational mitigation solutions, all aimed at improving scientific awareness of aviation’s non-CO2 climate impact.
... The Fit for 55 initiative consists of 16 separate communications with a particular focus on renewable energy sources, sustainable fuels, energy taxation and the transport sector. Around a quarter of GHG emissions in the EU now come from the transport sector alone and 4.4% of total emissions result from aviation. 1 In addition to the greenhouse gas carbon dioxide (CO2) and water vapor (H2O), aircrafts emit other gases and aerosol particles such as nitrogen oxides (NOx), sulfur dioxide (SO2) and soot which further increases the environmental and climate impact of air traffic (EASA, 2019;IPCC, 2022;Lee et al., 2009;Lee et al., 2021). Due to expected long-term passenger growth rates within the EU of around 2.5% per year and annual fuel efficiency improvements of only around 1%, aviation emissions are projected to increase in the future without additional measures (EASA, 2019;EEA, 2018;European Commission, 2021c). ...
Preprint
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This study analyzes the economic impacts of the Fit for 55 policy measures currently proposed by the European Commission for air transport. The methodology used in this paper is based on simulation modeling of different scenarios of how costs will increase and demand will decrease between 2023 and 2050. Various projected economic and key aviation-specific statistics serve as input variables for the model. The results indicate the following: All of the measures proposed by the European Commission have the potential to make flying more expensive, albeit to different degrees. Moreover, the full impacts of each measure take effect at different times in the future. Until 2035, the kerosene tax and the EU ETS have the largest impact on airline costs. The costs incurred by a SAF quota increase after 2035. The highest total cost impact is given in the medium term (2035-2040), when costs add up to 2.50 euros per 100 RPK in the reference scenario. With an increasing SAF ratio, the total cost impact decreases in the long run to 2.09 euros per 100 RPK in 2050. Assuming 100% pass-through to customers and negative price elasticities, the decrease in demand for intra-European transport amounts to a maximum of-23% in the reference scenario. Additional costs and decrease in demand are likely to be higher in the medium term (2035-2040) than in the long term (2050).
... One of the biggest challenges of our generation is the achievement of carbon neutrality [1]. The beginning of world air mobility, allied with trade globalization, promoted a substantial increase in the current fleet, responsible for the increment of the dependency on fossil fuel in the aviation sector. ...
Conference Paper
The demand for aviation fuel is constantly increasing and has become apprehensive due to the depletion of fossil fuels. The use of petroleum sourced fuels as an energy source in the air transportation industry consists of an unsustainable alternative. Due to this, the introduction of alternative jet fuel is required to mitigate these issues. Thus, the present work simulates single droplet combustion numerically in a drop tube furnace. In this context, jet-A1 and n-Hexadecane were investigated. Additionally, it is studied the validation of approximating the combustion of alternative jet fuel to n-hexadecane. The employed model consists of a two-way coupling approach between the fuel droplets and the carrier fluid following an Eulerian-Lagragangian schematic. The continuous phase is primarily modeled and further coupled with the fuel droplets known as the discrete phase. A combustion model is employed in order to simulate the natural phenomenon of single droplet combustion to the intended utilized fuels. The results reveal that the droplet diameter reduces as the time evolves under the representation of the d2 law enabling the computation of different combustion characteristics being affected by the fuel composition.
... Air travel is the most environmentally polluting mode of transport in climate change [9,26]. Aviation emissions are far more harmful than ground transport emissions [27]. 85% of global air transport CO 2 emissions in 2019 come from passenger transport, amounting to 785 million tonnes, an increase of 33% in total between 2013 and 2019 [2]. ...
Article
Global carbon emissions have been rapidly increasing in recent years, negatively influencing the global climate. Thereby, it is urgent to reduce carbon emissions and achieve carbon neutrality. During the COVID-19 pandemic, strict quarantine plans have led to a sharp decline in the number of international student flights, which will, in turn, decrease aviation carbon emissions. This study predicts the carbon emission reduction caused by the decrease in international student mobility during the COVID-19. The result shows that the carbon emission was about 1326 Gg, a staggering value equivalent to two-thirds of the carbon emissions of the UK’s agriculture sector in a year. Furthermore, this study analyzes the implications of current mitigation policies and makes recommendations for future strategies.
Article
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Aviation fleet globally grows in consequence of rise in ridership, number, and hour of flight. That makes the aviation sector one of the major contributors to the global warming threat. For this reason, environmental and ecologic aspects should be considered at least as much as performance at design step of an aircraft engine, namely aero-engine. To evaluate thermodynamics, environmental and ecologic aspects of an aero-engine a holistic approach is lack of the existing literature. The current paper presents the ecologic thermo-environmental index, as a novel measure, for evaluation of an aero-engine performance from a joint perspective of thermodynamics, ecological and environmental aspects. For better understanding of the dependence of ecologic thermo-environmental index on design parameters of the aero-engine a parametric study is also included. The rise in pressure ratio has an increasing impact on the ecologic thermo-environmental index whereas increase in the turbine inlet temperature also leads an increasing impact on the ecologic thermo-environmental index. On the other hand, the ecologic thermo-environmental index is found to be inversely proportional to the exergy efficiency. At the end of the study, the exergy efficiency of the turbojet engine is calculated to be varying from 44.46% to 57.12%. Additionally, the value of the ecologic thermo-environmental index of the turbojet engine ranges between 0.02 and 0.15. The author considers the present study to be beneficial to those interested in aerospace, mechanical, and environmental engineering.
Article
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From “flight shame” or flying consciousness to Stay Grounded and FlyingLess, calls for, and organized efforts to achieve, a marked decrease in flying in response to intensifying climate crisis abound. Of particular concern are frequent flyers, among whom are many in academia, especially in the high-income parts of the world. One manifestation is the proliferation of scholarship that critically analyzes academic flying while advocating for slower forms of travel, new forms of research and collaboration, and a low-greenhouse-gas-emitting academy more broadly. This conceptual article builds on that scholarship by engaging the growing literature calling for the decolonization of higher education institutions and the broader world. In doing so, and by attempting to bring into conversation two currently disconnected streams of literature, it explores how academic air travel both reflects and helps to reproduce patterns of colonial relations. Relatedly, the article considers how flying less contributes to the decolonization of higher education—especially in relation to “nature” and the appropriation of “the commons.” By insisting on the inextricable entanglement of society and nature, it thus illuminates how aeromobility-related consumption both arises from and reproduces persistent inequities born of imperialism and coloniality. On this basis, the article pushes advocates of reduced flying and of decolonization to engage one another in a common project to challenge disparities between peoples and places, as well as interspecies ones, as they relate to aeromobility, consumption, and political ecology.
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The recent improvement of technology readiness level in aeronautics and the renewed demand for faster transportation are driving the rebirth of supersonic flight for commercial aviation. However, the design of a future supersonic aircraft is still very challenging due to the complexity of several problems, such as static stability performance during the acceleration phase from subsonic speeds to supersonic speeds. Additionally, the interest of scientific community in open source numerical platform as a valid tool for a reliable and affordable aerodynamic design is considerably growing. In this framework, the present work addresses the aerodynamic performance of a Concorde-like aeroshape developed within the preliminary design of a high-speed civil transportation aircraft. Several flight conditions, ranging from subsonic to supersonic speeds, were investigated in detail by using Computational Fluid Dynamics. The aerodynamic force and moment coefficients are computed with fully three-dimensional and steady state Reynolds Average Navier-Stokes simulations, carried out in turbulent flow conditions. The effect of the Mach number variation on the shift of the aircraft aerodynamic center is detailed, by focusing on the aircraft pitching static stability. Flowfield numerical simulations are performed with both commercial (Ansys-Fluent) tool and open-source (SU2) code, which is also used extensively in multidisciplinary design procedures, for further comparisons. Particular attention is focused on the shift of the aeroshape aerodynamic center to verify that the provided wing design allows the aircraft static margin to be within 5% of the reference length, both at low-speed and high-speed flight conditions. The computed positions of the aerodynamic center are in agreement with the aeroshape surface pressure distributions and confirmed the literature results available for the Concorde aircraft. Therefore, in the view of future simulation campaigns for supersonic transportation aircraft, the present work aims to bridge the gap between previous aerodynamic design experiences, for instance matured on Concorde, and those carried out with modern CFD tools on full-scale aircraft, and on time-scales compatible with conceptual design practice. Finally, as the difference between the computed aerodynamic coefficients reflected mainly on drag computation performed with SU2, a special focus on numerical diffusion effect of the solver is also given and compared with a commercial certified CFD tool. This adds a unique further contribution to the SU2 community for aeronautics application.
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To meet ambitious climate targets, the aviation sector needs to neutralize CO2 emissions and reduce non-CO2 climatic effects. Despite being responsible for approximately two-thirds of aviation’s impacts on the climate, most of aviation non-CO2 species are currently excluded from climate mitigation efforts. Here we identify three plausible definitions of climate-neutral aviation that include non-CO2 forcing and assess their implications considering future demand uncertainty, technological innovation and CO2 removal. We demonstrate that simply neutralizing aviation’s CO2 emissions, if nothing is done to reduce non-CO2 forcing, causes up to 0.4 °C additional warming, thus compromising the 1.5 °C target. We further show that substantial rates of CO2 removal are needed to achieve climate-neutral aviation in scenarios with little mitigation, yet cleaner-flying technologies can drastically reduce them. Our work provides policymakers with consistent definitions of climate-neutral aviation and highlights the beneficial side effects of moving to aircraft types and fuels with lower indirect climate effects. Non-CO2 effects must be addressed for climate-neutral aviation but are currently ignored in international climate policies. The authors provide a framework with different definitions of climate neutrality, then show how technological and demand-side mitigation efforts can help to achieve these targets.
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V МІЖНАРОДНОЇ НАУКОВО-ТЕХНІЧНОЇ КОНФЕРЕНЦІЇ 14-15 квітня 2022 року Харків НТУ «ХПІ» 2022
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Aviation's fossil fuel emissions contribute to global warming. The production and disposal of the materials used in aircrafts too. The current metallic alloys present in the hot section of engines pose constraints in terms of temperature, pressure and weight that restrain the performance of the aircrafts. Also, these alloys are produced using rare, depleting resources, and polluting processes. In this paper, we hypothesize the use of bioinspired nacre-like alumina (NLA), a ceramic material that exhibits unusual toughness, and evaluate its potential as a replacement for superalloys in aircraft's engines. Comparing the performance of Ni superalloys and NLA in terms of properties, engine performance, and life cycle sustainability, we find NLA a promising alternative although progress has to be made with regards to its reliability, shaping, repair, and governance of the production process.
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In real gas turbines, multiple nozzles are used instead of a single-nozzle; therefore, interactions between flames are inevitable. In this study, the effects of flame-flame interaction on the emission characteristics and lean blowout limit were analysed in a CH 4 -fueled single- and dual-nozzle combustor. OH * chemiluminescence imaging showed that a flame-interacting region, where the two flames from the nozzles were merged, was present in the dual-nozzle combustor, unlike the single-nozzle combustor. Flow-field measurements using particle image velocimetry confirmed that a faster velocity region was formed at the flame merging region, thereby hindering flame stabilisation. In addition, we compared the emission indices of NO x and CO between the two combustors. The emission indices of CO were not significantly different; however, a distinct effect of flame-flame interaction was indicated in NO x . To understand the effect of flame-flame interaction on NO x emissions, we measured temperature distribution using a multi-point thermocouple. Results showed that a wider high-temperature region was formed in the dual-nozzle combustor compared to the single-nozzle combustor; this was attributable to the high OH * chemiluminescence intensity in the flame-interacting region. Furthermore, it was confirmed that the size of this interacting region caused the deformation of the temperature distribution in the combustor, which can induce a difference in the increase ratio of NO x emission between high and low equivalence ratio ranges. In conclusion, we confirmed that flame-flame interaction significantly affected temperature distribution in the downstream of the flame, and the change in temperature distribution contributed primarily to the varying concentration of the emission gas.
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Aviation accounts for approximately five percent of global greenhouse gas emissions through the combustion of fossil fuels. This paper analyses the opportunities and challenges of mitigation measures in limiting travel volume, energy and emission intensity to reduce the climate impact of aviation in Sweden. Several measures are in place that aim to reduce the climate impact of the aviation industry, ranging from regulations to technology alternatives to fossil-based jet fuel. These measures face several crosscutting challenges, many of which are of a socio-economic and political nature, and these aspects are often neglected in favour of focusing on technological solutions. The market creation for alternatives to fossil-based jet fuel is a major challenge, as most consumers today have a limited awareness of and willingness to pay for these innovations. Policy measures in place are proven ineffective in incentivising change. An understanding of the industry as a socio-technical system is required. The value of this review is its broader consideration of the pathways to reduce aviation's climate impact, offering new perspectives and pointing to areas for further research considering all components, their interactions and interdependence.
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The EU Emissions Trading Scheme (EU ETS) for air transport has been in force since 2012. Since 2013, CO2 emissions from flights within the EEA (European Economic Area = EU27 plus Norway, Iceland and Liechtenstein) have been regulated by the European ETS. In July 2021, a first proposal by the European Commission for a review of the current EU ETS has been published, as part of its ‘Fit for 55 package’, which shall then go through the legislative process. This revision of the EU ETS is likely to strengthen the existing scope and rules for aviation – also considering its interplay with the CORSIA (Carbon offsetting and reduction scheme for international aviation), the first global CO2 offsetting scheme for civil aviation. The challenges to be addressed by the revised EU ETS for aviation are manifold: the inclusion of aviation’s non-CO2 species (NOx, H2O, SOx, aerosols, contrails and contrail cirrus), the relationship between the EU-ETS and CORSIA, the contribution of air transport to the 2030 EU GHG reduction target and to the commitment to EU climate neutrality in 2050 (European Green Deal), the introduction of incentives for the use of sustainable aviation fuels (SAF), and its interplay with a potential taxation of kerosene. This paper discusses the pros and cons of different options for revising the current EU ETS for aviation. On this basis, recommendations for a revised EU ETS for air transport will be provided.
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Combustion in aircraft engines results in the formation of nitrogen oxides (NO x ) and carbon dioxide (CO 2 ), among other species. NO x impacts air quality and is an indirect contributor to radiative forcing, while CO 2 is a long-lived greenhouse gas. The International Civil Aviation Organization sets limits on NO x emissions from commercial aircraft, where for engines with a rated thrust greater than 89 kN the allowable NO x production per unit rated thrust is defined as a function of engine overall pressure ratio (OPR). This definition links the engine thermodynamic cycle, and implicitly fuel burn and CO 2 emissions, to allowable NO x levels. These regulations have historically been evaluated and implemented with a focus on reducing adverse air quality impacts around airports, but the thermodynamic efficiency tradeoff with CO 2 requires additional analysis to quantify net environmental impacts. This paper introduces a social cost basis for evaluating aviation NO x emissions regulations and quantifies the implied CO 2 and NO x attributable air quality damage, climate damage, and fuel costs associated with the emissions standard. We show that higher overall pressure ratio engines operating at the current NO x regulatory limit are allowed more environmental damage per unit rated thrust than lower overall pressure ratio engines, resulting in variable social costs per unit thrust (i.e. fuel and environmental costs combined) across the engine design space. This is a consequence of the definition of the regulation today, where higher pressure ratio engines are allowed higher NO x emissions. Alternative regulation definitions are evaluated which consider the engine cycle and combustor together. Achieving constant social costs requires a regulatory limit where the increase in allowed NO x emissions tapers off at higher pressure ratios, corresponding to the diminishing marginal efficiency improvements due to increasing OPR in that region.
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In the public debate on climate change in Europe, aviation transport has become a bone of contention and thus also a target of political regulation. While the actual available policy instruments, their designs and effects have been extensively studied, their political economy has remained a rather blind spot of research. Therefore, in this article we explore factors accounting for the instrument choice in aviation policy. Revealing most different evolutions in this matter, the Netherlands and Germany represent appropriately illustrative cases for a comparative exploration. Based on the Political Process-inherent Dynamics Approach, we shed light on a highly complex and limiting institutional environment for aviation policy-making and ultimately identify diverging conceptions of problem structures as well as different configurations of party competition as main explanatory factors for instrument choice and aviation policy evolution.
Technical Report
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This article provides a review of the role of stochastic approaches, in particular Monte Carlo calculations, in the study of aviation-induced contrails at different characteristic lengths, ranging from micrometers to the planetary scale. Pioneered in the 1960s by Bird, Direct Simulation Monte Carlo has for long time been considered unfeasible in extended dispersed-phase systems as clouds. Due to the impressive increase in computational power, Lagrangian Monte Carlo approaches are currently available, even for studying cloud formation and evolution. Some aspects of these new approaches are reviewed after a detailed introduction to the topic of aircraft-induced cloudiness. The role of Monte Carlo approaches in reducing the different source of uncertainty about the contribution of aviation contrails to climate change is introduced. Perspectives on their role in future experimental and theoretical studies are discussed throughout the paper.
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With the rapid development of China's civil aviation, carbon emissions have brought severe environmental problems. Understanding the internal dynamic relationship between carbon emission and air transportation development is conducive for the industry to realize green development more effectively. Based on the Tapio decoupling theory, this study investigated the decoupling status between civil aviation carbon dioxide (CO2) emissions and transportation revenue. A three-dimension decomposition model was constructed and applied to further explore the influencing factors of various decoupling status. The empirical study resulted in three key findings. Firstly, there is still much room for efficiency improvement in civil aviation overall transportation process. Compared with the external economic environment and the production process, the improvement of civil aviation operation process needs to be further strengthened. Secondly, the civil aviation carbon emission decoupling status was dominated by negative decoupling. The growth of air transportation revenue still deeply depends on the fossil fuel consumption. Thirdly, the decline of potential energy intensity significantly propels the decoupling progress of China's civil aviation; meanwhile, external economic environment and potential transportation intensity are key inhibitors of the decoupling development.
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Aviation emissions are responsible for an estimated 24,000 premature mortalities annually and 3.5% of anthropogenic radiative forcing (RF). Emissions of nitrogen and sulfur oxides (NO x and SO x ) contribute to these impacts. However, the relative contributions and mechanisms linking these emissions to formation and impacts of secondary aerosols (as opposed to direct aerosol emissions) have not been quantified, including how short-lived aerosol precursors at altitude can increase surface-level aerosol concentrations. We apply global chemistry transport modeling to identify and quantify the different chemical pathways to aerosol formation from aviation emissions, including the resulting impact on radiative forcing. We estimate a net aerosol radiative forcing of –8.3 mWm ⁻² , of which –0.67 and –7.8 mWm ⁻² result from nitrate and sulfate aerosols respectively. We find that aviation NO x causes –1.7 mWm ⁻² through nitrate aerosol forcing but also –1.6 mWm ⁻² of sulfate aerosol forcing by promoting oxidation of SO 2 to sulfate aerosol. This accounts for 21% of the total sulfate forcing, and oxidation of SO 2 due to aviation NO x is responsible for 47% of the net aviation NO x attributable RF. Aviation NO x emissions in turn account for 41% of net aviation-aerosol-attributable RF (non-contrail). This is due to ozone-mediated oxidation of background sulfur and the “nitrate bounce-back" effect, which reduces the net impact of sulfur emissions. The ozone-mediated mechanism also explains the ability of cruise aviation emissions to significantly affect surface aerosol concentrations. We find that aviation NO x emissions cause 72% of aviation-attributable, near-surface aerosol loading by mass, compared to 27% from aviation SOx emissions and less than 0.1% from direct emission of black carbon. We conclude that aviation NO x and SO x emissions are the dominant cause of aviation-attributable secondary inorganic aerosol radiative forcing, and that conversion of background aerosol precursors at all altitudes is amplified by enhanced production of aviation attributable oxidants at cruise altitudes.
In this paper, a mathematical model for estimating the performance and flight trajectories in cruise is identified from data available in flight manuals. The first part of this paper focuses on the design of a fuel flow and emissions model. Starting from the equations of motion of an aircraft in cruise, a simplified model representing the fuel flow in a corrected form was developed. A practical algorithm was next developed to identify the aircraft model parameters and to determine the mathematical structure that reflects its fuel flow. This process was done using performance data available in the aircraft flight crew operating manual. The emissions model was also developed based on data available in the International Civil Aviation Organization’s engine emissions databank. The second part of the paper deals with the development of algorithms for predicting the trajectories and calculating the optimal speeds (i.e., maximum range, long range, and economy) of the aircraft in cruise. Practical techniques for storing and retrieving information without using optimization algorithms have been considered. The methodology was applied on both a Cessna Citation X business jet and Bombardier CRJ-700 regional jet aircraft. The comparison results showed a very good agreement for the fuel consumption and optimal speed.
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Wuhan Tianhe International Airport (WUH) was suspended to contain the spread of COVID-19, while Shanghai Hongqiao International Airport (SHA) saw a tremendous flight reduction. Closure of a major international airport is extremely rare and thus represents a unique opportunity to straightforwardly observe the impact of airport emissions on local air quality. In this study, a series of statistical tools were applied to analyze the variations in air pollutant levels in the vicinity of WUH and SHA. The results of bivariate polar plots show that airport SHA and WUH are a major source of nitrogen oxides. NOx, NO2 and NO diminished by 55.8%, 44.1%, 76.9%, and 40.4%, 33.3% and 59.4% during the COVID-19 lockdown compared to those in the same period of 2018 and 2019, under a reduction in aircraft activities by 58.6% and 61.4%. The concentration of NO2, SO2 and PM2.5 decreased by 77.3%, 8.2%, 29.5%, right after the closure of airport WUH on 23 January 2020. The average concentrations of NO, NO2 and NOx scatter plots at downwind of SHA after the lockdown were 78.0%, 47.9%, 57.4% and 62.3%, 34.8%, 41.8% lower than those during the same period in 2018 and 2019. However, a significant increase in O3 levels by 50.0% and 25.9% at WUH and SHA was observed, respectively. These results evidently show decreased nitrogen oxides concentrations in the airport vicinity due to reduced aircraft activities, while amplified O3 pollution due to a lower titration by NO under strong reduction in NOx emissions.
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This work examines changes in cirrus cloud cover in possible association with aviation activities at congested air corridors. The analysis is based on the latest version of the International Satellite Cloud Climatology Project D2 data set and covers the period 1984&ndash1998. Over areas with heavy air traffic, the effect of large-scale modes of natural climate variability such as ENSO, QBO and NAO as well as the possible influence of the tropopause variability, were first removed from the cloud data set in order to calculate long-term changes of observed cirrus cloudiness. The results show increasing trends in cirrus cloud coverage, between 1984 and 1998, over the high air traffic corridors of North America, North Atlantic and Europe, which in the summertime only over the North Atlantic are statistically significant at the 99.5% confidence level (2.6% per decade). In wintertime however, statistically significant changes at the 95% confidence level are found over North America, amounting to +2.1% per decade. Statistically significant increases at the 95% confidence level are also found for the annual mean cirrus cloud coverage over the North Atlantic air corridor (1.2% per decade). Over adjacent locations with lower air traffic, the calculated trends are statistically insignificant and in most cases negative both during winter and summer in regions studied. Moreover, it is shown that the longitudinal distribution of decadal changes in cirrus cloudiness along the latitude belt centered at the North Atlantic air corridor, parallels the spatial distribution of fuel consumption from highflying air traffic, providing an independent test of possible impact of aviation on contrail cirrus formation. Results from this study are compared with other studies and different periods of records and it appears as evidenced in this and in earlier studies that there exists general agreement on the aviation effect on high cloud trends.
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Three-dimensional (latitude, longitude, altitude) global inventories of civil and military aircraft fuel burned and emissions have been developed for the United States National Aeronautics and Space Administration (NASA) for the years 1976, 1984, and 1992, and by the European Abatement of Nuisances Caused by Air Transport (ANCAT)/European Commission (EC) Working Group and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) for 1991/92. For 1992, the results of the inventory calculations are in good agreement, with total fuel used by aviation calculated to be 129.3 Tg (DLR), 131.2 Tg (ANCAT), and 139.4 Tg (NASA). Total emissions of NOx (as N02) in 1992 were calculated to range from 1.7 Tg (NASA) to 1.8 Tg (ANCAT and DLR). Forecasts of air travel demand and technology developed by NASA and ANCAT for 2015 have been used to create three-dimensional (3-D) data sets of fuel burn and NOx emissions for purposes of modeling the near-term effects of aircraft. The NASA 2015 forecast results in a global fuel burn of 309 Tg, with a NOx emission of 4.1 Tg (as N02); the global emission index, EI(NOx) (g NOx/kg fuel), is 13.4. In contrast, the ANCAT 2015 forecast results in lower values-a global fuel burn of 287 Tg, an emission of 3.5 Tg of NOx and a global emission index of 12.3. The differences arise from the distribution of air travel demand and technology assumptions.
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Rising global air traffic and its associated contrails have the potential for affecting climate via radiative forcing. Current estimates of contrail climate effects are based on coverage by linear contrails that do not account for spreading and, therefore, represent the minimum impact. The maximum radiative impact is estimated by assuming that long-term trends in cirrus coverage are due entirely to air traffic in areas where humidity is relatively constant. Surface observations from 1971 to 1995 show that cirrus increased significantly over the northern oceans and the United States while decreasing over other land areas except over western Europe where cirrus coverage was relatively constant. The surface observations are consistent with satellite-derived trends over most areas. Land cirrus trends are positively correlated with upper-tropospheric (300 hPa) humidity (UTH), derived from the National Centers for Environmental Prediction (NCEP) analyses, except over the United States and western Europe where air traffic is heaviest. Over oceans, the cirrus trends are negatively correlated with the NCEP relative humidity suggesting some large uncertainties in the maritime UTH. The NCEP UTH decreased dramatically over Europe while remaining relatively steady over the United States, thereby permitting an assessment of the cirrus-contrail relationship over the United States. Seasonal cirrus changes over the United States are generally consistent with the annual cycle of contrail coverage and frequency lending additional evidence to the role of contrails in the observed trend. It is concluded that the U.S. cirrus trends are most likely due to air traffic. The cirrus increase is a factor of 1.8 greater than that expected from current estimates of linear contrail coverage suggesting that a spreading factor of the same magnitude can be used to estimate the maximum effect of the contrails. From the U.S. results and using mean contrail optical depths of 0.15 and 0.25, the maximum contrail-cirrus global radiative forcing is estimated to be 0.006-0.025 W m-2 depending on the radiative forcing model. Using results from a general circulation model simulation of contrails, the cirrus trends over the United States are estimated to cause a tropospheric warming of 0.2°-0.3°C decade-1, a range that includes the observed tropospheric temperature trend of 0.27°C decade-1 between 1975 and 1994. The magnitude of the estimated surface temperature change and the seasonal variations of the estimated temperature trends are also in good agreement with the corresponding observations.
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Within the EU-project TRADEOFF, the impact of NOx (=NO+NO2) emissions from subsonic aviation upon the chemical composition of the atmosphere has been calculated with focus on changes in reactive nitrogen, ozone, and the chemical lifetime of methane. We apply a 3-D chemical transport model that includes comprehensive chemistry for both the troposphere and the stratosphere and uses various aircraft emission scenarios developed during TRADEOFF for the year 2000. The environmental effects of enhanced air traffic along polar routes and of possible changes in cruising altitude are investigated. In the reference case the model predicts aircraft-induced maximum increases of zonal-mean NOy (=total reactive nitrogen) between 156 pptv (August) and 322 pptv (May) in the tropopause region of the Northern Hemisphere. Resulting maximum increases in zonal-mean ozone vary between 3.1 ppbv in September and 7.7 ppbv in June. The lifetime of methane is calculated to decrease by 0.71%, inducing a radiative forcing of -6.4 mW/m2. Enhanced use of polar routes implies significantly larger zonal-mean ozone increases in high Northern latitudes during summer, while the effect is negligible in winter. Lowering the flight altitude leads to smaller ozone increase in the lower stratosphere and upper troposphere, and to larger ozone increase at lower altitudes. Regarding total ozone change, the degree of cancellation between these two effects depends on latitude and season, but annually and globally averaged the stratospheric decrease dominates, mainly due to washout of NOy in the troposphere, which weakens the tropospheric increase. Raising flight altitudes increases the ozone burden both in the troposphere and the lower stratosphere, primarily due to a more efficient accumulation of pollutants in the stratosphere.
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A chemistry-climate model has been applied to study the radiative forcings generated by aircraft NOx emissions through changes in ozone and methane. Four numerical experiments, where an extra pulse of aircraft NOx was emitted into the model atmosphere for a single month (January, April, July, or October), were compared to a control experiment, allowing the aircraft impact to be isolated. The extra NOx produces a short-lived (few months) pulse of ozone that generates a positive radiative forcing. However, the NOx and O3 both generate OH, which leads to a reduction in CH4. A detailed analysis of the OH budget reveals the spatial structure and chemical reactions responsible for the generation of the OH perturbation. Methane's long lifetime means that the CH4 anomaly decays slowly (perturbation lifetime of 11.1 years). The negative CH4 anomaly also has an associated negative O3 anomaly, and both of these introduce a negative radiative forcing. There are important seasonal differences in the response of O3 and CH4 to aircraft NOx, related to the annual cycle in photochemistry; the O3 radiative forcing calculations also have a seasonal dependence. The long-term globally integrated annual mean net forcing calculated here is approximately zero, although earlier work suggests a small net positive forcing. The model design (e.g., upper tropospheric chemistry, convection parameterization) and experimental setup (pulse magnitude and duration) may somewhat influence the results: further work with a range of models is required to confirm these results quantitatively.
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Reducing methane (CH4) emissions is an attractive option for jointly addressing climate and ozone (O3) air quality goals. With multidecadal full-chemistry transient simulations in the MOZART-2 tropospheric chemistry model, we show that tropospheric O3 responds approximately linearly to changes in CH4 emissions over a range of anthropogenic emissions from 0–430 Tg CH4 a−1 (0.11–0.16 Tg tropospheric O3 or ∼11–15 ppt global mean surface O3 decrease per Tg a−1 CH4 reduced). We find that neither the air quality nor climate benefits depend strongly on the location of the CH4 emission reductions, implying that the lowest cost emission controls can be targeted. With a series of future (2005–2030) transient simulations, we demonstrate that cost-effective CH4 controls would offset the positive climate forcing from CH4 and O3 that would otherwise occur (from increases in NOx and CH4 emissions in the baseline scenario) and improve O3 air quality. We estimate that anthropogenic CH4 contributes 0.7 Wm−2 to climate forcing and ∼4 ppb to surface O3 in 2030 under the baseline scenario. Although the response of surface O3 to CH4 is relatively uniform spatially compared to that from other O3 precursors, it is strongest in regions where surface air mixes frequently with the free troposphere and where the local O3 formation regime is NOx-saturated. In the model, CH4 oxidation within the boundary layer (below ∼2.5 km) contributes more to surface O3 than CH4 oxidation in the free troposphere. In NOx-saturated regions, the surface O3 sensitivity to CH4 can be twice that of the global mean, with >70% of this sensitivity resulting from boundary layer oxidation of CH4. Accurately representing the NOx distribution is thus crucial for quantifying the O3 sensitivity to CH4.
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This work examines changes in cirrus cloud cover in possible association with aviation activities at congested air corridors. The analysis is based on the latest version of the International Satellite Cloud Climatology Project D2 data set and covers the period 1984&ndash1998. Over areas with heavy air traffic, the effect of large-scale modes of natural climate variability such as ENSO, QBO and NAO as well as the possible influence of the tropopause variability, were first removed from the cloud data set in order to calculate long-term changes of observed cirrus cloudiness. The results show increasing trends in cirrus cloud coverage, between 1984 and 1998, over the high air traffic corridors of North America, North Atlantic and Europe, which in the summertime only over the North Atlantic are statistically significant at the 99.5% confidence level (2.6% per decade). In wintertime however, statistically significant changes at the 95% confidence level are found over North America, amounting to +2.1% per decade. Statistically significant increases at the 95% confidence level are also found for the annual mean cirrus cloud coverage over the North Atlantic air corridor (1.2% per decade). Over adjacent locations with lower air traffic, the calculated trends are statistically insignificant and in most cases negative both during winter and summer in regions studied. Moreover, it is shown that the longitudinal distribution of decadal changes in cirrus cloudiness along the latitude belt centered at the North Atlantic air corridor, parallels the spatial distribution of fuel consumption from highflying air traffic, providing an independent test of possible impact of aviation on contrail cirrus formation. Results from this study are compared with other studies and different periods of records and it appears as evidenced in this and in earlier studies that there exists general agreement on the aviation effect on high cloud trends.
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Aviation is an integral part of the global economic and transportation systems. In fact, aviation expansion outpaces the economic growth. Projections indicate that over the next 2 decades, the demand for aviation could grow to about 3 times its present level. This projected growth will likely result in higher aviation emissions and associated impacts on the environment and on human health and welfare, depending upon a variety of factors (such as the size and mix of the operational fleet necessary to meet the stated demand, as well as mitigation steps that could include new technological advances, more efficient operational procedures, market-based options, or regulatory intervention). Nonetheless, it is critical to balance the economic benefits of air travel with environmental concerns associated with this projected aviation growth.
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We have performed new calculations of the radiative forcing due to changes in the concentrations of the most important well mixed greenhouse gases (WMGG) since pre-industrial time. Three radiative transfer models are used. The radiative forcing due to CO2, including shortwave absorption, is 15% lower than the previous IPCC estimate. The radiative forcing due to all the WMGG is calculated to 2.25 Wm−2, which we estimate to be accurate to within about 5%. The importance of the CFCs is increased by about 20% relative to the total effect of all WMGG compared to previous estimates. We present updates to simple forcing-concentration relationships previously used by IPCC.
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A structurally highly simplified, globally integrated coupled climate-economic costs model SIAM (Structural Integrated Assessment Model) is used to compute optimal paths of global CO2 emissions that minimize the net sum of climate damage and mitigation costs. The model is used to study the sensitivity of the computed optimal emission paths with respect to various critical input assumptions. The climate module is represented by a linearized impulse-response model calibrated against a coupled ocean-atmosphere general circulation climate model and a three-dimensional global carbon-cycle model. The cost terms are represented by strongly simplified expressions designed for maximal transparency with respect to sensitive input assumptions. These include the discount rates for mitigation and damage costs, the inertia of the socio-economic system, and the dependence of climate damages on the change in temperature and the rate of change of temperature. Different assumptions regarding these parameters are believed to be the cause of the marked divergences of existing cost-benefit analyses based on more sophisticated economic models. The long memory of the climate system implies that very long time horizons of several hundred years need to be considered to optimize CO2 emissions on time scales relevant for a policy of sustainable development. Cost-benefit analyses over shorter time scales of a century or two can
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The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow the changes in the tropospheric distributions of the two major radiatively-active trace gases, methane and tropospheric ozone, following the emission of pulses of the short-lived tropospheric ozone precursor species, methane, carbon monoxide, NOx and hydrogen. The radiative impacts of NOx emissionswere dependent on the location chosen for the emission pulse, whether at the surface or in the upper troposphere or whether in the northern or southern hemispheres. Global warming potentials were derived for each of the short-lived tropospheric ozone precursor species by integrating the methane and tropospheric ozone responses over a 100 year time horizon. Indirect radiative forcing due to methane and tropospheric ozone changes appear to be significant for all of the tropospheric ozone precursor species studied. Whereas the radiative forcing from methane changes is likely to be dominated by methane emissions, that from tropospheric ozone changes is controlled by all the tropospheric ozone precursor gases, particularly NOxemissions. The indirect radiative forcing impacts of tropospheric ozone changes may be large enough such that ozone precursors should be considered in the basket of trace gases through which policy-makers aim to combat global climate change.
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The global impact of shipping on atmospheric chemistry and radiative forcing, as well as the associated uncertainties, have been quantified using an ensemble of ten state-of-the-art atmospheric chemistry models and a pre-defined set of emission data. The analysis is performed for present-day conditions (year 2000) and for two future ship emission scenarios. In one scenario ship emissions stabilize at 2000 levels; in the other ship emissions increase with a constant annual growth rate of 2.2% up to 2030 (termed the "Constant Growth Scenario" (CGS)). Most other anthropogenic emissions follow the IPCC (Intergovernmental Panel on Climate Change) SRES (Special Report on Emission Scenarios) A2 scenario, while biomass burning and natural emissions remain at year 2000 levels. An intercomparison of the model results with observations over the Northern Hemisphere (25°–60° N) oceanic regions in the lower troposphere showed that the models are capable to reproduce ozone (OH<sub>3</sub>) and nitrogen oxides (NOx=NO+NOH<sub>2</sub>) reasonably well, whereas sulphur dioxide (SOH<sub>2</sub>) in the marine boundary layer is significantly underestimated. The most pronounced changes in annual mean tropospheric NOH<sub>2</sub> and sulphate columns are simulated over the Baltic and North Seas. Other significant changes occur over the North Atlantic, the Gulf of Mexico and along the main shipping lane from Europe to Asia, across the Red and Arabian Seas. Maximum contributions from shipping to annual mean near-surface OH<sub>3</sub> are found over the North Atlantic (5–6 ppbv in 2000; up to 8 ppbv in 2030). Ship contributions to tropospheric OH<sub>3</sub> columns over the North Atlantic and Indian Oceans reach 1 DU in 2000 and up to 1.8 DU in 2030. Tropospheric O<sub>3</sub> forcings due to shipping are 9.8±2.0 mW/m<sup>2</sup> in 2000 and 13.6±2.3 mW/m<sup>2</sup> in 2030. Whilst increasing OH<sub>3</sub>, ship NOx simultaneously enhances hydroxyl radicals over the remote ocean, reducing the global methane lifetime by 0.13 yr in 2000, and by up to 0.17 yr in 2030, introducing a negative radiative forcing. The models show future increases in NOx and OH<sub>3</sub> burden which scale almost linearly with increases in NOx emission totals. Increasing emissions from shipping would significantly counteract the benefits derived from reducing SOH<sub>2</sub> emissions from all other anthropogenic sources under the A2 scenario over the continents, for example in Europe. Globally, shipping contributes 3% to increases in OH<sub>3</sub> burden between 2000 and 2030, and 4.5% to increases in sulphate under A2/CGS. However, if future ground based emissions follow a more stringent scenario, the relative importance of ship emissions will increase. Inter-model differences in the simulated OH<sub>3</sub> contributions from ships are significantly smaller than estimated uncertainties stemming from the ship emission inventory, mainly the ship emission totals, the distribution of the emissions over the globe, and the neglect of ship plume dispersion.
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Simplified climate models can be used to calculate and to compare temperature response contributions from small forcings without the need for considerable computer resources. A linear climate response model using Green’s functions has been formulated to calculate radiative forcing (RF) and the global mean temperature response from aviation. The model, LinClim, can calculate aviation RF for CO2, O3, CH4, water vapour, contrails, sulphate and black carbon aerosols. From these RFs, temperature responses may be calculated for individual effects in order to determine their relative importance by applying preliminary values for efficacies. The LinClim model is tuned to reproduce the dominant mode of its parent coupled atmosphere-ocean GCM, ECHAM4/OPYC3. LinClim is able to reproduce the IPCC (1999) 2050 aviation-related forcings. The model is shown through some example application analyses to be a useful tool for exploring the effects of aviation on RF and temperature response.
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