Chemistry transport models play a crucial role in the evaluation of the effect of anthropogenic emissions on the atmosphere and climate, but they come with high computational costs and require specialized know-how. This renders them impractical for applications in multidisciplinary optimisation, or regulatory and operational decision-making processes where environmental effects are to be considered. Such applications require computationally efficient surrogate models of the complex chemistry transport models. Here we investigate the use of data-driven discovery and reduced-order modelling methods for this purpose. Specifically, we examine the dynamic mode decomposition (DMD) and proper orthogonal decomposition coupled with the sparse identification of non-linear dynamics (POD-SINDy). We evaluate their ability to reconstruct and forecast changes in the distribution of ozone in response to the introduction of supersonic aircraft as modelled by the GEOS-Chem chemistry transport model. Of the tested methods, we find that optimized DMD and bagging optimized DMD with constrained eigenvalues perform best. These methods can reconstruct and forecast full-atmospheric ozone responses for up to several years without losing stability, at smaller errors than estimates using the spatio-temporal mean of the data. On average, the constrained optimized DMD method reduces the reconstruction error by 63.5 % and that of forecasting by 25.8 % compared to the spatio-temporal mean. For the constrained bagging optimized DMD these reductions are 45.0 % and 23.1 %, respectively. The resulting change in global ozone column, calculated from the reconstructed atmospheres, has an error smaller than 10 %. This is achieved while reducing the computational and storage requirements by several orders of magnitude, which may be a worthwhile tradeoff for some applications.

With renewed interest in the development of civil supersonic aircraft, their return in the future is becoming more ever more likely. The environmental impact of emissions in the stratosphere on climate and the ozone layer therefore needs to be explored. The stratospheric ozone levels determine the amount of harmful ultraviolet radiation reaching the Earth's surface and thus the level of risk to human health and ecosystems. Ozone response is complex, varying with emission altitude and latitude and we are currently reliant on computationally expensive chemistry-transport models to calculate chemical species concentration changes resulting from supersonic aviation emissions. This paper takes a novel approach to reduce the dependency on these models, creating data-driven dynamical systems that model the global spatiotemporal atmospheric ozone response for different emission scenarios. The dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) methods are applied to atmospheric ozone data obtained from the GEOS-Chem model, and the evolution of the dominant POD spatial modes are modelled using sparse identification of nonlinear dynamics algorithm (SINDy). We show that DMD models can reconstruct monthly global column ozone changes with root mean square errors less than 0.05 Dobson unit (DU) for a period of three years. Predicting the global mean column ozone changes for the years beyond the period used to construct the models, results in errors less than 0.12 DU. Independent DMD models at two different altitudes can be interpolated to produce estimates for ozone response at an intermediate altitude. These methods can serve as a basis for low dimensional surrogate models that can be used to evaluate chemical species concentrations changes as a result of supersonic aviation emissions.

The increasing demand for sustainable aircraft solutions has encouraged the development of non-CO􁊼 emitting aircraft designs. Currently, a number of theoretically successful designs have been created by parties such as the Massachusetts Institute of Technology, National Aeronautics and Space Administration, and The Technical University of Delft. Unfortunately, these radical aircraft redesigns are too risky to conceive, requiring massive amounts of investment and research. Since growth of the global aviation industry will only persist if aircraft greenhouse gas emissions are reduced, airlines have been looking for more fuel efficient aircraft, and the demand for green solutions has skyrocketed1. Thus, in this study the A320appu is proposed in an effort to significantly decrease the environmental footprint of aviation while limiting the risks and cost that accompany novel designs. This is done trough a conversion of the A320neo to use a hybrid, multi-fuel power and propulsion system. By replacing the traditional kerosene Auxiliary Power Unit (APU) with a hydrogen engine and an aft mounted, boundary layer ingesting propulsor, the design will enter the narrow-body market as an intermediate step between current generation kerosene-powered aircraft and more distant radical redesigns, like the Flying V2 or the Aurora D8 3. The APU is thus adapted into an Auxiliary Power and Propulsion Unit (APPU). This single aisle, short-medium haul airliner was specifically chosen for this conversion because aircraft of this class are expected to comprise 80% of all aircraft sales by 2038. The reconfigured A320neo, coined the A320appu, shall provide an economically feasible and green alternative. It shall be the first advance towards normalising hydrogen within the aviation industry.

The challenges of designing the A320appu are to maintain low development costs, integrating the cutting edge subsystem and reassessing aircraft parameters such as the stability and controllability or range. Moreover the Operating Empty Weight (OEW) increases because of the added subsystems, and as the A320appu is designed for the same Maximum Take-off Weight (MTOW), the available payload decreases. The A320appu is designed such that the increase of the OEW is minimised, while maximising the integrability by limiting the amount of changes to the A320neo. Furthermore, significant reduction of the 𝐶𝑂􁊼 emissions and local pollution have to be ensured, while providing similar performance to the A320neo. To achieve the aforementioned points, four main changes to the A320neo are proposed below and thereafter discussed in more detail.