ULTRAFINE AEROSOL-PARTICLES IN AIRCRAFT PLUMES - IN-SITU OBSERVATIONS

Measurements of ultrafine particles in the near field of the DLR resea rch aircraft ATTAS using low (0.02g/kg fuel) and high (2.7g/kg) fuel s ulfur contents (FSCs) are presented. Soot emissions of similar to 10(1 5)/kg show no significant dependence on FSC. Strong evidence is found that similar to 1/3 of the soot particles must be involved in ice nucl eation in contrails, in addition to freezing of newly formed volatile particles. In the absence of contrails, numbers of volatile particles with diameters D > 5 nm reach similar to 10(17)/kg for high FSC, and s till reach similar to 10(16)/kg for low FSC. A clear contribution of H 2SO4 to volatile particle growth is observed. If growth is exclusively linked to H2SO4, the S to H2SO4 conversion efficiency increases with decreasing FSC. Depletion of ultrafine particles is observed in contra ils, very likely due to scavenging by contrail ice crystals.