EU H2020 Research and Innovation Action


Advancing the Science for Aviation and Climate

1 January 2020 to 30 June 2023

ACACIA, a Horizon 2020 Research and Innovation Action coordinated by the DLR-Institute of Atmospheric Physics, started in January 2020 with a kick-off event in Oberpfaffenhofen. In total, 11 participants from 7 European countries cooperate in ACACIA.
ACACIA will organise the next conference on transport and climate TAC-5 2022 end of June 2022 in South Germany. Abstract submission is open until 28 February 2022.

New Paper within ACACIA:
The uncertain impact of aviation soot particles on natural cirrus clouds

Righi et al. 2021 "Exploring the uncertainties in the aviation soot-cirrus effect"

Aviation soot particles emitted by aircraft have the potential to act as ice nucleating particles, competing with other ice formation processes in natural cirrus clouds and thus modifying their radiative properties. The quantifications of the resulting climate impact are, however, still affected by considerable uncertainties and large disagreement exists among the various modelling studies. In a recent study by Righi et al. 2021, a newly-developed configuration of the global aerosol-climate model EMAC-MADE3 has been applied to explore the uncertainties of the impact of aviation-soot on natural cirrus clouds. A large number of numerical simulations has been performed to assess the sensitivity of the aviation soot-cirrus effect on the ice nucleation abilities of aviation soot and to the model’s representation of the vertical updrafts which lead to cirrus cloud formation.
With this method, a radiative forcing from the aviation soot-cirrus effect in the range of −35 to +13 mW m−2 has been quantified, but with a confidence level below 95% in several cases. To further explore the sensitivity of this estimate to model dynamics, simple idealized experiments with prescribed constant vertical velocities have been performed. They show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about ±1.7 of further uncertainty to the model estimates of the aviation soot-cirrus radiative forcing.
Currently ongoing international collaboration in the framework of the ACACIA European Horizon 2020 project will provide additional insights on the ice nucleation abilities of aviation soot by means of laboratory measurements and will contribute to refine the assessment on this effect in follow-up studies.


Righi, M., Hendricks, J., and Beer, C. G.: Exploring the uncertainties in the aviation sootcirrus effect, Atmos. Chem. Phys., 21, 17267-17289,, 2021.

Requests and inquiries: ACACIA Project Office

This Project is funded by the EU under Grant Agreement No 875036.