An increasingly important property of fuels is sooting tendency. Soot emissions from combustion devices contribute to ambient fine particulates, which cause millions of deaths worldwide each year , and they are the dominant source of black carbon, which is the second largest cause of global warming . The impact of soot on climate change is particularly pronounced in aviation: not only is the radiative forcing (RF) from aviation-generated black carbon almost one-third that of aviationemitted CO2 (9.5 vs. 35 mW/m 2 ), but soot particles are the primary nucleation source for aviation-induced cirrus (AIC), which has the largest RF due to aviation (50 mW/m 2 ). Experiments with aircraft flying in tandem have demonstrated that contrail formation from the lead plane is reduced if it is burning sustainable aviation fuels (SAFs) with low aromatics content .