In Situ Observations of Ice Particle Losses in a Young Persistent Contrail

We describe results of in situ observations of a 1‐ to 2‐min‐old contrail in the vortex phase generated from soot‐rich exhaust (>10 15 emitted soot particles per kilogram of fuel burned). Simultaneous measurements of soot (EI soot ) and apparent ice (AEI ice ) particle number emission indices show a pronounced anticorrelation in the vertical contrail profile. AEI ice decrease by about 75% with increasing distance below the contrail‐producing aircraft, while EI soot increase by an equivalent relative fraction, therefore strongly suggesting ice particle formation to be soot‐controlled and losses to be caused by sublimation. Quantifying these losses in measurements helps to validate and improve contrail parameterizations used to estimate the climate impact of contrails and contrail cirrus. Our study further demonstrates the challenges in the performance and interpretation of particle measurements in young contrails and lends itself to suggestions for improving contrail data evaluation.