Revisiting Contrail Ice Formation: Impact of Primary Soot Particle Sizes and Contribution of Volatile Particles

Area of Science:

• Atmospheric Science
• Climate Science
• Aviation Emissions

Background:

• Aircraft contrails significantly contribute to aviation's non-CO2 climate impact.
• Contrail formation is primarily linked to soot particles emitted from aircraft engines.
• Previous studies assumed aggregate soot size determined particle activation.

Purpose of the Study:

• To investigate the role of primary soot particle size versus aggregate size in contrail formation.
• To explain observed fractions of soot particles forming contrail ice particles during ECLIF campaigns.
• To assess the impact of changing soot properties on contrail ice particle number and climate effects.

Main Methods:

• Analysis of soot particle activation during contrail formation.
• Comparison of primary soot particle sizes with aggregate sizes.
• Modeling of contrail plume supersaturation and volatile particle contribution.

Main Results:

• Primary soot particle size, not aggregate size, governs nonvolatile particle activation in contrails.
• Smaller primary soot sizes delay ice formation onset and increase plume supersaturation.
• This leads to a higher probability of volatile particles contributing to contrail ice.
• The conditions favoring volatile particle contribution are broader than previously assumed.

Conclusions:

• Contrail formation dynamics are critically influenced by primary soot particle characteristics.
• Future reductions in soot primary size from sustainable aviation fuels may widen volatile particle influence.
• Further research is needed to understand the climate implications of evolving soot properties and contrail formation.