EGU24-17410, updated on 11 Mar 2024
https://doi.org/10.5194/egusphere-egu24-17410
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Towards an improved treatment of (semi) volatile particle activation in contrail models

Joel Ponsonby, Roger Teoh, and Marc Stettler
Joel Ponsonby et al.
  • Department of Civil and Environmental Engineering, Imperial College London, London, SW7 2AZ, United Kingdom

Contrails are estimated to account for the majority of the present-day warming by the aviation industry. Their formation relies on the availability of aerosol in the exhaust plume, upon which water vapour can condense and subsequently freeze to form contrail ice crystals Most modern aircraft operate in the soot-rich regime, releasing soot particles with a number emission index (EIn) of between 1014 and1016 (kg-fuel)-1. Under these conditions, the number concentration of soot particles and contrail ice crystals scales linearly. For this reason, existing global contrail simulations typically assume that the number concentration of ice crystals and soot particles are equivalent. However, the use of alternative fuels such as sustainable aviation fuel (SAF) and liquid hydrogen, and the adoption of cleaner lean-burn combustors in the existing fleet are likely to drive the soot EIn into the soot-poor regime < 1013 (kg-fuel)-1. Here, (semi) volatile material and entrained ambient particles can compete with soot for plume supersaturation and the relationship between the number concentration of soot particles and contrail ice crystals is non-linear. These effects are not currently accounted for in existing contrail models used to simulate regional and global contrail climate forcing.  

In this work, we extend the parcel model proposed by Kärcher et al. [1] to account for the activation of volatile particulate matter (vPM) in the soot-poor regime and integrate this into the contrail cirrus prediction model (CoCiP) [2]. We explore the relationship between the soot EIn and the apparent ice emissions index (AEI) in the soot-rich and soot-poor regimes, evaluating the model’s sensitivity to different aerosol properties, including particle hygroscopicity and characteristics of the particle size distribution. Preliminary results show a linear relationship between the soot EIn and AEI in the soot-rich regime, consistent with previous work [1]. However, in the soot-poor regime, the AEI: (i) could be up to two orders of magnitude larger than the soot EIn; (ii) increases with decreasing ambient temperatures and (iii) depends on the assumed particle properties of the (semi) volatile and ambient particle modes. These results suggest that existing global contrail simulations may underestimate the contrail climate forcing for a small subset of flights with soot EIn < 1014 (kg-fuel)-1.

The model developed in this work will be implemented in a global contrail simulation, incorporating activation of vPM. A sensitivity analysis will also be performed, and the results validated with in-situ measurements from the recent Emissions and Climate Impact of Alternative Fuels (ECLIF) III experimental campaign [3].

References

[1] Bernd Kärcher et al., Journal of Geophysical Research: Atmospheres, 2015, 120, 7893–7927.

[2] Ulrich Schumann, Geoscientific Model Development, 2012, 5, 43–580.

[3] Raphael Märkl et al., [EGUsphere preprint].

How to cite: Ponsonby, J., Teoh, R., and Stettler, M.: Towards an improved treatment of (semi) volatile particle activation in contrail models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17410, https://doi.org/10.5194/egusphere-egu24-17410, 2024.