Fig. 4: Apparent ice emission indices (AEI) from contrail measurements.
From: Fuel sulfur content can modulate contrail ice crystal numbers
a Ice particle number per kg of fuel burned using ultra-low-sulfur HEFA-SPK (green), low-sulfur Jet A-1 (dark gray), and medium-sulfur blend fuel (blue). Measurements were performed in the far field in the 50–300 s old contrail at 9620–9730 m altitude and air temperatures 9–11 K below TSA. Measurements sequences are divided according to the relative humidity over ice of the ambient air. Boxes extend from the first quartile to the third quartile of the data, with a black line indicating the median and white boxes indicating mean values. The whiskers extend to the maximum and minimum data points. Due to the scatter caused by the varying measurement conditions, no statistically significant conclusion can be drawn from the comparison of Jet A-1 and HEFA-SPK. b Mean AEI from far-field (95% < RHi < 100%) vs nvPM emission indices from near-field measurements (squares), including uncertainty intervals. Differences in engine and combustor operating conditions between the near and far field can result in increased nvPM emissions in the far field (see the section “Particle and trace gas measurements”), as reflected by the extended error bars. Jet A-1 and HEFA-SPK test points from the earlier ECLIF3-1 campaign measured at supersaturated atmospheric conditions are shown as black and lightgreen pentagons, including uncertainty intervals according to Märk et al. and Dischl et al. 22,33. The dashed line represents the 1:1 relationship between AEI and nvPM EI.
