Impact on flight trajectory characteristics when avoiding the formation of persistent contrails for transatlantic flights

This paper studies the impacts on flight trajectories, such as lateral and vertical changes, when avoiding the formation of persistent contrails for transatlantic flights. A sophisticated Earth-System Model (EMAC) coupled with a flight routing submodel (AirTraf) and a contrail submodel (CONTRAIL) is used to optimize flight trajectories concerning the flight time and the flight distance through contrail forming regions (contrail distance). All the trajectories are calculated taking into account the effects of the actual and local meteorological parameters, e.g., wind, temperature, relative humidity, etc. A full-year simulation has been conducted based on a daily flight schedule of 103 transatlantic flights. The trade-off between the flight time and contrail distance shows a large daily variability, meaning for the same increase in flight time, the reduction in contrail distance varies from 20% to 80% depending on the daily meteorological situation. The results confirm that the overall changes in flight trajectories follow a seasonal cycle corresponding to the nature of the potential contrail coverage. In non-summer seasons, the southward and upward shifts of the trajectories are favorable to avoid the contrail formation. In summer, the northward and upward shifts are preferred. A partial mitigation strategy for up to 40% reduction in contrail distance can be achieved throughout all the seasons with a negligible increase in flight time (less than 2%), which represents a reasonable trade-off between flight time increase and contrail avoidance.Aircraft Noise and Climate Effect

Cost-Benefit Assessment of Climate and Weather Optimized Trajectories for Different North Atlantic Weather Patterns

Besides CO2, the climate impact of commercial aviation is strongly influenced by non-CO2 effects, which are highly sensitive to meteorological conditions and their spatial variations. To assess the cost-benefit potential (climate impact mitigation vs. cost increase) of climate and weather optimized flight trajectories in the North Atlantic flight corridor, optimal control techniques are applied. However, the execution of multi-criteria route optimizations for an intercontinental route network and various weather patterns is computationally highly intensive. Since computational resources are limited, a reduced surrogate route network is generated and evaluated first with regard to the computational effort, the coverage in terms of available seat kilometers, as well as the accuracy of reproducing the original route network with regard to climate impact. The proposed reduced route network consists of 40 routes (original network: 1,359) and is able to reproduce the climate impact of the original route network with reasonable climate impact deviations of 2.5%. The evaluation of climate and weather optimized trajectories is performed for the top route of the surrogate network. The maximum climate impact reduction potential is differing strongly from 9% up to 60% for varying North Atlantic weather patterns. Averaged over the weather patterns, a maximum climate impact mitigation potential of about 32%, going along with a cost increase of about 8% has been estimated. However, at a cost penalty of 1%, a potential climate impact reduction of 24% has been observedAircraft Noise and Climate Effect

Transport Patterns of Global Aviation NOx and their Short-term O3 Radiative Forcing: A Machine Learning Approach

Aviation produces a net climate warming contribution that comprises multiple forcing terms of mixed sign. Aircraft NOx emissions are associated with both warming and cooling terms, with the short-term increase in O3 induced by NOx emissions being the dominant warming effect. The uncertainty associated with the magnitude of this climate forcer is amongst the highest out of all contributors from aviation and is owed to the non-linearity of the NOx–O3 chemistry and the large dependency of the response on space and time, i.e., on the meteorological condition and background atmospheric composition. This study addresses how transport patterns of emitted NOx and their climate effects vary with respect to regions (North America, South America, Africa, Eurasia and Australasia) and seasons (January–March and July–September in 2014) by employing global-scale simulations. We quantify the climate effects from NOx emissions released at 250 hPa (~ 10 400 m) in terms of radiative forcing resulting from their induced short-term contributions to O3. The emitted NOx is transported with Lagrangian air parcels within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. To identify the main global transport patterns and associated climate impacts of the 14 000 simulated air parcel trajectories, the unsupervised QuickBundles clustering approach is adapted and applied. Results reveal a strong seasonal dependence of the contribution of NOx emissions to O3. For most regions, a negative correlation is found between an air parcel’s downward transport and its mean contribution to O3. NOx emitted in the Northern regions (North America and Eurasia) experiences the longest residence times in upper midlatitudes (40–45 % of their lifetime), while those beginning in the South (South America, Africa and Australasia) remain mostly in the Tropics (45–50 % of their lifetime). Due to elevated O3 sensitivities, emissions in Australasia induce the highest overall radiative forcing, attaining values that are larger by factors of 2.7 and 1.2 relative to Eurasia during January and July, respectively. The location of the emissions does not necessarily correspond to the region that will be most affected – for instance, NOx over North America in July will induce the largest radiative forcing in Europe. Overall, this study highlights the spatially and temporally heterogeneous nature of the NOx–O3 chemistry from a global perspective, which needs to be accounted for in efforts to minimize aviation’s climate impact, given the sector’s resilient growth.Aircraft Noise and Climate Effect

A Lagrangian study of globally emitted aviation NOx and associated short-term O3 radiative forcing effects

The resilient growth of air travel demands a comprehensive understanding of the climate effects from aviation emissions. The current level of knowledge of the environmental repercussions of CO2 emissions is considerably higher than that of non-CO2 emissions, which includes nitrogen oxides (NOx), sulfur oxides (SOx), other aerosols like black carbon (BC), water vapor and contrails. Aircraft NOx emissions not only possess a high degree of uncertainty because of the non-linearity of the NOx – O3 chemistry, but are also responsible for producing the second strongest net warming effect out of all non-CO2 climate forcers from aviation, right after contrails [1]. This study employs global-scale simulations to characterize the transport patterns of nitrogen oxides and assess their climate effects across several regions (North America, South America, Africa, Eurasia and Australasia) from January to March and July to September in 2014. Radiative forcing effects from the short-term increase in O3, which are triggered by NOx emissions, are estimated. These emissions, which are introduced at a typical cruising altitude, are modelled as Lagrangian air parcels that are transported within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model [2]. In order to summarize the dynamical and radiative forcing characteristics of more than 10,000 simulated trajectories, a clustering approach with an adapted distance metric is applied. The method itself is an unsupervised machine learning algorithm, called QuickBundles [3], that is most commonly used in the field of neuroscience. A strong seasonal dependence is found for the contribution of NOx emissions to O3. In terms of residence times, NOx emitted in Northern regions resides mainly in the upper mid-latitudes while those initiated in the South remain mostly in the Tropics. Due to pronounced zonal jets, the location of emission does not necessarily correspond to the region that will be most affected, i.e., an emission starting in N. America in July will induce the greatest warming in Europe.[1] Lee, D.S., Fahey, D.W., Skowron, A., Allen, M.R., Burkhardt, U., Chen, Q., Doherty, S.J., Freeman, S., Forster, P.M., Fuglestvedt, J., Gettelman, A., De León, R.R., Lim, L.L., Lund, M.T., Millar, R.J., Owen, B., Penner, J.E., Pitari, G., Prather, M.J., Sausen, R., Wilcox, L.J.: The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018, Atmospheric Environment, Volume 244, 2021, 117834, ISSN 1352-2310, https://doi.org/10.1016/j.atmosenv.2020.117834.[2] Jöckel, P., Kerkweg, A., Pozzer, A., Sander, R., Tost, H., Riede, H., Baumgaertner, A., Gromov, S., Kern, B., Development cycle 2 of the Modular Earth Submodel System (MESSy2), Geoscientific Model Development, 3, 717-752, doi: 10.5194/gmd-3-717-2010, 2010.[3] Garyfallidis, E., Brett, M., Correia, M. M., Williams, G. B., Nimmo-Smith, I. QuickBundles, a Method for Tractography Simplification. Frontiers in neuroscience, 6, 175. https://doi.org/10.3389/fnins.2012.00175, 2012.Aircraft Noise and Climate Effect

The analysis of the climate mitigation potential in terms of O3-Radiative Forcing from aviation NOx using O3 algorithmic climate change functions

Aviation contributes to 3.5% of anthropogenic climate change in terms of Effective Radiative Forcing (ERF) and 5% in terms of temperature change. Aviation climate impact is expected to increase rapidly due to the growth of air transport sector in most regions of the world and the effects of the COVID-19 pandemic are expected to only have a temporary effect on this growth. While efforts have been made to curb CO2 emissions, non-CO2 effects that are at least equally significant according to recent research, require more attention. The EU Horizon 2020 project ClimOp considers a comprehensive approach to tackling the climate impact of aviation using novel operational measures. One such measure is climate-optimised flight planning, where small deviations can be made in aircraft trajectories to minimise their overall climate impact. Algorithmic Climate Change Functions (aCCFs) are used to estimate the climate impact of local non-CO2 effects such as nitrogen oxide (NOx) emissions (via ozone (O3) formation and methane (CH4) depletion), aviation water vapour (H2O) and contrails using weather variables directly as inputs. By using these functions in an air traffic optimisation module, climate sensitive regions are detected and avoided leading to climate-optimised trajectories. Here, we focus specifically on evaluating the effectiveness of reducing the aviation NOx induced climate impact via O3 formation, using only O3 aCCFs for the optimisation strategy. This is achieved using the chemistry climate model EMAC (ECHAM5/MESSy) and various submodels. A summer and winter day, characterised by high spatial variability of O3 aCCFs are selected, following which, air traffic over the European airspace is optimised with respect to climate as well as operating cost. The air traffic is laterally and vertically optimised separately to enable an evaluation of the horizontal and vertical pattern of O3 aCCFs. It is shown that despite the significant impact of the synoptic situation on the transport of emitted NOx, the climate-optimised flights lead to lower O3 Radiative Forcing (RF) compared to the cost-optimised flights. The study finds that while O3 aCCFs can reduce the climate impact, there are certain discrepancies in the prediction of O3 impact from aviation NOx emissions, as seen for the selected summer day. Although the aCCFs concept is a rough simplification in predicting future pathways of emissions and subsequent climate impact, we could show that it enables a reasonable first estimate. Further research is required to better describe the aCCFs allowing an improved estimate in O3-RF reduction for optimisation approaches.Aircraft Noise and Climate Effect

Analysis of aircraft routing strategies for north atlantic flights by using airtraf 2.0

Climate-optimized routing is an operational measure to effectively reduce the climate impact of aviation with a slight increase in aircraft operating costs. This study examined variations in the flight characteristics among five aircraft routing strategies and discusses several characteristics of those routing strategies concerning typical weather conditions over the North Atlantic. The daily variability in the North Atlantic weather patterns was analyzed by using the European Center Hamburg general circulation model (ECHAM) and the Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model in the specified dynamics mode from December 2008 to August 2018. All days of the ten complete winters and summers in the simulations were classified into five weather types for winter and into three types for summer. The obtained frequency for each of the weather types was in good agreement with the literature data; and then representative days for each weather type were selected. Moreover, a total of 103 North Atlantic flights of an Airbus A330 aircraft were simulated with five aircraft routing strategies for each representative day by using the EMAC model with the air traffic simulation submodel AirTraf. For every weather type, climate-optimized routing shows the lowest climate impact, at which a trade-off exists between the operating costs and the climate impact. Cost-optimized routing lies between the time-and fuel-optimized routings and achieves the lowest operating costs by taking the best compromise between flight time and fuel use. The aircraft routing for contrail avoidance shows the second lowest climate impact; however, this routing causes extra operating costs. Our methodology could be extended to statistical analysis based on long-term simulations to clarify the relationship between the aircraft routing characteristics and weather conditions.Aircraft Noise and Climate Effect

Case Study for Testing the Validity of NOx-Ozone Algorithmic Climate Change Functions for Optimising Flight Trajectories

One possibility to reduce the climate impact of aviation is the avoidance of climate-sensitive regions, which is synonymous with climate-optimised flight planning. Those regions can be identified by algorithmic Climate Change Functions (aCCFs) for nitrogen oxides (NOx), water vapour (H2O) as well as contrail cirrus, which provide a measure of climate effects associated with corresponding emissions. In this study, we evaluate the effectiveness of reducing the aviation-induced climate impact via ozone (O3) formation (resulting from NOx emissions), when solely using O3 aCCFs for the aircraft trajectory optimisation strategy. The effectiveness of such a strategy and the associated potential mitigation of climate effects is explored by using the chemistry–climate model EMAC (ECHAM5/MESSy) with various submodels. A summer and winter day, characterised by a large spatial variability of the O3 aCCFs, are selected. A one-day air traffic simulation is performed in the European airspace on those selected days to obtain both cost-optimised and climate-optimised aircraft trajectories, which more specifically minimised a NOx-induced climate effect of O3 (O3 aCCFs). The air traffic is laterally and vertically re-routed separately to enable an evaluation of the influences of the horizontal and vertical pattern of O3 aCCFs. The resulting aviation NOx emissions are then released in an atmospheric chemistry–climate simulation to simulate the contribution of these NOx emissions to atmospheric O3 and the resulting O3 change. Within this study, we use O3-RF as a proxy for climate impact. The results confirm that the climate-optimised flights lead to lower O3-RF compared to the cost-optimised flights, although the aCCFs cannot reproduce all aspects of the significant impact of the synoptic situation on the transport of emitted NOx. Overall, the climate impact is higher for the selected summer day than for the selected winter day. Lateral re-routing shows a greater potential to reduce climate impact compared to vertical re-routing for the chosen flight altitude. We find that while applying the O3 aCCFs in trajectory optimisation can reduce the climate impact, there are certain discrepancies in the prediction of O3 impact from aviation NOx emissions, as seen for the summer day. Although the O3 aCCFs concept is a rough simplification in estimating the climate impact of a local NOx emission, it enables a reasonable first estimate. Further research is required to better describe the O3 aCCFs allowing an improved estimate in the Average Temperature Response (ATR) of O3 from aviation NOx emissions. A general improvement in the scientific understanding of non-CO2 aviation effects could make climate-optimised flight planning practically feasibleAircraft Noise and Climate Effect

Newly developed aircraft routing options for air traffic simulation in the chemistry–climate model EMAC 2.53: AirTraf 2.0

Aviation contributes to climate change, and the climate impact of aviation is expected to increase further. Adaptations of aircraft routings in order to reduce the climate impact are an important climate change mitigation measure. The air traffic simulator AirTraf, as a submodel of the European Center HAMburg general circulation model (ECHAM) and Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model, enables the evaluation of such measures. For the first version of the submodel AirTraf, we concentrated on the general setup of the model, including departure and arrival, performance and emissions, and technical aspects such as the parallelization of the aircraft trajectory calculation with only a limited set of optimization possibilities (time and distance). Here, in the second version of AirTraf, we focus on enlarging the objective functions by seven new options to enable assessing operational improvements in many more aspects including economic costs, contrail occurrence, and climate impact. We verify that the AirTraf setup, e.g., in terms of number and choice of design variables for the genetic algorithm, allows us to find solutions even with highly structured fields such as contrail occurrence. This is shown by example simulations of the new routing options, including around 100 North Atlantic flights of an Airbus A330 aircraft for a typical winter day. The results clearly show that AirTraf 2.0 can find the different families of optimum flight trajectories (three-dimensional) for specific routing options; those trajectories minimize the corresponding objective functions successfully. The minimum cost option lies between the minimum time and the minimum fuel options. Thus, aircraft operating costs are minimized by taking the best compromise between flight time and fuel use. The aircraft routings for contrail avoidance and minimum climate impact reduce the potential climate impact which is estimated by using algorithmic climate change functions, whereas these two routings increase the aircraft operating costs. A trade-off between the aircraft operating costs and the climate impact is confirmed. The simulation results are compared with literature data, and the consistency of the submodel AirTraf 2.0 is verified.Aircraft Noise and Climate Effect