Aerosol and contrail particles in a young exhaust plume of an Airbus A310-300 were characterized with respect to size distribution and refractive index at plume ages ≤2 sec. The instrumentation included standard particle spectrometers (PCASP-100X, FSSP-300) and a new instrument (Multiangle Aerosol Spectrometer Probe, MASP) for simultaneous measurement of particle size and refractive index. The particle size distributions as measured with the standard FSSP-300 and the new MASP showed good agreement. The observed refractive indices indicated a mixture of pure ice particles, black carbon aerosol, and an internal mixture of these components in the contrail, while black carbon and sulfate-containing compounds dominated the upper tropospheric background aerosol. ¿ 1998 American Geophysical Union