Contrail processed aviation soot aerosol are poor ice nucleating particles at cirrus temperatures

Aviation soot surrogates processed in contrails are believed to become potent ice nuclei at cirrus temperature. This is not verified for real aviation soot, that can have vastly different physico-chemical properties. Here, we sampled soot particles from in-use commercial aircraft engines and quantified the effect of contrail processing on their ice nucleation ability at T < 228 K. We show that aviation soot becomes compacted upon contrail processing but this does not change their ice nucleation ability in contrast to other soot types. The presence of H ₂SO ₄ condensed in soot pores, the highly fused nature of the soot primary particles and their arrangement limit the volume of pores generated upon contrail processing, limiting sites for ice nucleation. Furthermore, we hypothesized that contrail processed aviation soot particles emitted from alternative jet fuel would also be poor ice nucleating particles if their emission sizes remain small (< 150 nm).