Impact of aircraft NOx and aerosol emissions on atmospheric composition : a model intercomparison
Authors: Cohen Yann , Hauglustaine Didier , Bellouin Nicolas , Eastham Sebastian , Lund Marianne Tronstadt , Matthes Sigrun , Skowron Agnieszka , Thor Robin 
Published: February 2023

Aircraft emissions consist of carbon dioxide (CO2), nitrogen oxides (NOx), sulfur dioxide (SO2) and particulate matter (black carbon, sulfate) and water vapour. The non-CO2 effects have been recently evaluated as twice the CO2 effects regarding their radiative forcing of climate in 2018 [1]. Among the non-CO2 effects, nitrogen oxides emissions impact several greenhouse gases concentrations. Increased tropospheric ozone production results in a positive radiative forcing (climate impact), but the subsequent increased OH concentrations enhance methane chemical destruction, thus decreasing stratospheric water vapour and the methane-linked background ozone levels in the troposphere. The net radiative forcing caused by the aircraft NOx emissions is evaluated as a net positive forcing but still shows important uncertainties.In order to investigate representation of key mechanisms involved for climate forcing, in the framework of the ACACIA (Advancing the Science for Aviation and Climate) EU project, six global chemistry-climate models have been used to reevaluate the climate effects of NOx and aerosol aircraft emissions on atmospheric composition following a common protocol. As a first step, the standard runs have been assessed regarding ozone, carbon monoxide (CO), water vapour and reactive nitrogen (NOy) against the IAGOS airborne measurements during 1994-2018, separately in the upper troposphere and in the lower stratosphere.As a second step, the models have been used to assess the impact of NOx and aerosol emissions on atmospheric composition. The subsonic aircraft perturbations are calculated based on the CEDS aircraft emission inventories [2] for the present-day conditions and based on different socioeconomic scenarios [3] for future (2050) conditions. Several sensitivity simulations will be presented in order to investigate the sensitivity of the results to background atmospheric conditions (present, future) and to lightning emissions. The changes in atmospheric composition will be presented and compared for the different models and scenarios.&#160;Acknowledgement:This study was supported by the European Union&#8217;s Horizon 2020 research and innovation programme under grant agreement No 875036 within the Aeronautics project ACACIA.&#160;References:[1] D.S. Lee, D.W. Fahey, A. Skowron, M.R. Allen, U. Burkhardt, Q. Chen, S.J. Doherty, S. Freeman, P.M. Forster, J. Fuglestvedt, A. Gettelman, R.R. De Le&#243;n, L.L. Lim, M. T. Lund, R.J. Millar, B. Owen, J.E. Penner, G. Pitari, M.J. Prather, R. Sausen, and L. J. Wilcox, Atmospheric Environment 244, 117834 (2021)[2] R. M. Hoesly, S. J. Smith, L. Feng, Z. Klimont, G. Janssens-Maenhout, T. Pitkanen, J. J. Seibert, L. Vu, R. J. Andres, R. M. Bolt, T. C. Bond, L. Dawidowski, N. Kholod, J. Kurokawa, M. Li, L. Liu, Z. Lu, M. C. P. Moura, P. R. O&#8217;Rourke, and Q. Zhang, Geosci. Model Develop. 11, 369-408 (2018)[3] M. J. Gidden, K. Riahi, S. J. Smith, S. Fujimori, G. Luderer, E. Kriegler, D. P. van Vuuren, M. van den Berg, L. Feng, D. Klein, K. Calvin, J. C. Doelman, S. Frank, O.Fricko, M. Harmsen, T. Hasegawa, P. Havlik, J. Hilaire, R. Hoesly, J. Horing, A. Popp, E. Stehfest, and K. Takahashi, Geosci. Model Develop. 12, 1443-1475 (2019)