The impact of flight altitude on short-term NOx-O3 climate effects – a global multi-method assessment

Abstract

Aside from the climate impacts from carbon dioxide (CO2) emissions, civil aircraft currently in operation also emit nitrogen oxides (NOx), water vapor (H2O) and other non-CO2 pollutants whose combined primary and secondary effects account for almost 70% of aviation's net contribution towards anthropogenic global warming. NOx emissions, in the short-run, actuate the second largest aviation warming effect via indirect ozone (O3) formation [1], and, unlike CO2, the altitude, geographic location and time of emission are all significant drivers of their resulting climate impact. Past studies [2] have shown a positive correlation between emission altitude and warming from NOx emitted within the troposphere, but such analyses are frequently limited by emission inventories that largely focus on flights across the North Atlantic Flight Corridor (NAFC), thereby disregarding future shifts and alternate patterns in civil aviation traffic. We bridge this gap via global, Lagrangian and Eulerian simulations using the EMAC model wherein equal amounts of NO are released across five regions during two seasons, as was done in [3], but now for two additional flight levels that together cover typical subsonic cruise ranges of 10–12 km. The NOx-induced O3 production was calculated using two modelling methods, tagging and perturbation, as both are vastly used for climate effects estimations. The former is used to compute the contribution of a source to a whole while the latter is useful, for instance, in quantifying the total impact from variations in the strength of a source. We therefore characterize the relation between emission altitude and warming from short-term O3 on a global scale. These results and analyses then form an integral part of the development of next-generation surrogate models that will make climate-optimal routing a reality [4].

References
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[4] Rao, P., Dwight, R., Singh, D., Maruhashi, J., Dedoussi, I., Grewe, V., and Frömming, C.: Towards a new surrogate model for predicting short-term NOx-O3 effects from aviation using Gaussian processes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4337, https://doi.org/10.5194/egusphere-egu23-4337, 2023.

Acknowledgements
This research is part of the ACACIA (Advancing the Science for Aviation and Climate; http://www.acacia-project.eu) project, which is funded by the European Commission, Horizon 2020 Framework program under the grant agreement no. 875036.
This study used the Dutch national e-infrastructure with the support of the SURF Cooperative (grant nos. EINF-441 and EINF-2734).