Elemental composition and morphology of ice-crystal residual particles in cirrus clouds and contrails

Aircraft sampling of residual particles from evaporated ice crystals was performed using a Counterflow Virtual Impactor. Samples of crystals taken in both contrails and cirrus clouds were compared with interstitial aerosols found in natural cirrus. The samples were analyzed with a scanning electron microscope which was equipped with a windowless energy-dispersive X-ray detector (SEM/EDX). In the contrail and cirrus cases black carbon (BC) particles dominated the residual size spectra for particles smaller than 1 μm. The coarse residual particle mode (Dp≥1.5 μm) in contrails consisted almost completely of mechanically generated metallic particles which contributed only about 1% to residual particle number but approximately 50% to residual particle volume. Observed particle number concentrations and BC mass concentration of the residual particles were 0.2 cm−3 and 16 ng m−3 inside the contrail and 0.02 cm−3 and <2 ng m−3 inside the cirrus. The fraction of BC particles (0.1 μm<Dp<0.8 μm) in the interstitial aerosol samples increased with altitude from <70% at 8 km to 95% at 11 km near the air-traffic corridors with number concentrations of ≈0.1 cm−3.