Airborne particle measurements during NASA project SUCCESS have shown that particle concentration profiles serve as good indicators of aircraft exhaust plume encounters. During exhaust plume penetrations there is a strong anticorrelation between the ratio of nonvolatile/total particulates and Nitrogen Oxide (NO) concentrations. An increase in fuel sulfur content was found to increase the total particle emission index, while the nonvolatile emission index remained unchanged. The EI's increased by a factor of 2.6 as the fuel sulfur increased from 70--700 ppm. The large particle size distribution (200--400 nm) was seen as a good long term indicator of an aircraft exhaust plume. ¿ 1998 American Geophysical Union