Airborne Measurements of Ice Particle Concentrations in Contrails

At present, contrail cirrus contribute the largest single component to the climate impact from aviation, even surpassing the radiative forcing from its CO ₂ emissions. One pathway to mitigate the warming by contrail cirrus might be the reduction of ice number concentrations in contrails. In this context, observations of the relation between particle emissions from the aircraft's engine and ice crystals nucleating in contrails are needed. This research also helps to quantify the effects of sustainable alternative jet fuels on contrails.

To investigate biofuel effects on aviation emission and contrail formation, the NDMAX/ECLIF II in-situ measurement campaign took place in Ramstein, Germany in January and February 2018. During the aircraft campaign, the NASA DC-8 chased the DLR A320 ATRA, fueled with biofuel blends with varying aromatic content. The reference fuel was Jet A1 with 19.5% aromatic content, blended with the biofuel HEFA (hydro-processed esters and fatty acids) in compositions of 30:70 and 50:50. Eight science flights were performed over northern Germany, during which the DC-8 regularly crossed the A320 plume at distances between 2.7 and 20 NM. An FFSSP-300 (Fast Forward Scattering Spectrometer Probe) positioned next to a CO ₂ inlet, was optimized to measure the ice particle concentrations in the contrails. The instrument calibration and new data analysis including particle-by-particle data will be presented.

A statistical set of 170 contrail encounters was evaluated and the dependence of the apparent ice emission indices AEI _ice on ambient conditions like altitude, humidity and temperature, in addition to engine settings like fuel flow and Mach number, will be analysed. In summary, the campaign provides an extensive data set to investigate sustainable alternative fuel effects on contrails.