The role of volatile particulate matter in simulated contrail AEI ice compared to the Boeing ecoDemonstrator campaign

Preliminary data analyses from the 2023 joint NASA and Boeing ecoDemonstrator campaign indicate that volatile particulate matter (vPM) contributed significantly to the measured ice emissions indices (AEI ice) as non-volatile PM (i.e., soot) emissions were very low for the particular engine studied. Similarly, as the fuel sulfur contents of the two primary fuels tested during the campaign were also very low, it is likely that lubrication oil vented from the engine into the core flow of the exhaust made up a large portion of the vPM; however, there is very little measurement data to verify this claim. Widely available modelling tools are now starting to include simplified vPM activation parameterizations in their contrail ice formation schemes, without the necessary data for evaluation. This may overstate the climate impacts of the simulated contrails, which has broader implications on contrail mitigation strategies.

In this study, the pycontrails model was adapted to include the properties of the fuels used during the ecoDemonstrator campaign. The current vPM activation scheme in the model follows a competition-based, temperature-dependent approach for ice formation, where a constant vPM concentration competes for available water vapor with emitted soot particles (non-volatile PM) and ambient aerosol particles. Temperature values are sourced from meteorological input data to the model that is subject to some uncertainty. To test the temperature sensitivity of the vPM activation scheme on the predicted AEI ice, this study will compare model output between meteorological initializations using ERA5 reanalysis data and similar parameters measured during the 2023 ecoDemonstrator campaign. Comparisons are also made with measured AEI ice values.

This study will provide insights into how simple treatments of particle activation are likely to be highly influenced by the input assumptions of the model. The findings will help to determine future campaign goals that aim to make measurements of vPM more thoroughly as well as identify key sensitivities to test in future contrail modeling intercomparison projects.