In situ observations of particles in jet aircraft exhausts and contrails for different sulfur containing fuels

The impact of sulfur oxides on particle formation and contrails is investigated in the exhaust plume of a twin-engine jet aircraft. Different fuels were used with sulfur mass fractions of 170 and 5500 ppm in the fuel, one lower than average, the other above the specification limit of standard Jet-A1 fuel. During various phases of the same flight, the two engines burnt either high or low sulfur fuel or different fuels in the two engines. Besides visual, photo and video observations from close distance, in situ measurements were made within the plumes at plume ages of 20 to 30 s, at altitudes between 9 and 9.5 km, and temperatures between -49 and -55 C. The data include particle number densities for particles larger than 7 nm, 18 nm, 120 nm, and 1 #mu#m in diameter, together with wind, temperature and humidity measurements. The observations show visible and measurable differences between contrails caused by the different sulfur levels. At ambient temperatures 5 K below the threshold temperature for contrail onset, the plume became visible about 10 m after the engine exit for high sulfur content, but 15 m after the engine exit for low sulfur content. The higher sulfur emission caused a larger optical thickness of the contrail shortly after onset, with slightly brown colored contrail when observed with the sun in the back, and more contrast when viewed against the sun. The high-sulfur contrail grew more quickly but also evaporated earlier than the low-sulfur contrail. (orig./KW)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman