06 Nov 2023
 | 06 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Soot aerosol from commercial aviation engines are poor ice nucleating particles at cirrus cloud temperatures

Baptiste Testa, Lukas Durdina, Peter A. Alpert, Fabian Mahrt, Christopher H. Dreimol, Jacinta Edebeli, Curdin Spirig, Zachary C. J. Decker, Julien Anet, and Zamin A. Kanji

Abstract. Ice nucleating particles catalyse ice formation in clouds, affecting climate through radiative forcing from aerosol-cloud interactions. Aviation directly emits particles into the upper troposphere where ice formation conditions are favourable. Previous studies have used proxies of aviation soot to estimate their ice nucleation activity, however the investigations with commercial aircraft soot from modern in-use aircraft engine have not been quantified. In this work, we sample aviation soot particles at ground level from different commercial aircraft engines to test their ice nucleation ability at temperatures ≤ 228 K, as a function of engine thrust and soot particle size. Additionally soot particles were catalytically stripped to reveal the impact of mixing state on their ice nucleation ability. Particle physical and chemical properties were further characterised and related to the ice nucleation properties. The results show that aviation soot nucleates ice at or above relative humidity conditions required for homogeneous freezing of solution droplets (RHhom).We attribute this to a mesopore paucity inhibiting pore condensation and the sulfur content which suppresses freezing. Only large soot aggregates (400 nm) emitted under 30–100 % thrust conditions for a subset of engines (2/10) nucleate ice via pore condensation and freezing. For those specific engines, the presence of hydrophilic chemical groups facilitates the nucleation. Aviation soot emitted at thrust ≥100 % (sea level thrust) nucleates ice at or above RHhom. Overall our results suggest that aviation soot will not contribute to natural cirrus formation and can be used in models to update impacts of soot-cirrus clouds.

Baptiste Testa et al.

Status: open (until 24 Dec 2023)

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  • RC1: 'Comment on egusphere-2023-2441', Anonymous Referee #1, 07 Dec 2023 reply

Baptiste Testa et al.

Baptiste Testa et al.


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Short summary
Laboratory experiments on the ice nucleation of real commercial aviation soot particles are investigated for their cirrus cloud formation potential. Our results show that aircraft emitted soot in the upper troposphere will be poor ice nucleating particles. Measuring the soot particle morphology and modifying their mixing state allows us to elucidate why these particles are ineffective at forming ice, in contrast to previously used soot surrogates.