Observation on tropospheric aerosol particles was carried out on 27 April 1991 over Tsukuba, Japan. Aerosol particles collected in the upper troposphere at 7.5 km altitude were studied by electron microscopy. Soot-containing particles were collected in a large number fraction (0.53) of the submicron particles. Such a high proportion of soot particles in the upper troposphere has not been reported in previous research. From the X-ray analysis, Vanadium was also detected in some of the particles, indicating the origin of oil combustion. The oil-well fires in Kuwait are likely to be the origin of these soot particles. Calculated trajectories of the air suggested that these particles over Japan had circled the globe. ¿ American Geophysical Union 1992