The residence time of a particle within a spatial domain is the total time it spends within this domain. We study the residence time of small dense particles in a spreading line vortex. Trajectories have been calculated for small dense particles released near a spreading line vortex. The results show that particles released far away from the vortex center will not be trapped by it, but particles released close to it will remain there for a considerable time. This residence time is shown to be a function of the particle inertia &tgr;p, its fall velocity VT, and the vortex's Reynolds number Re&ggr;. The results of simulations also show that there is an optimum vortex Reynolds number such that the residence time of the particle is maximized within this simulated spreading line vortex. These findings are expected to be applicable to the coupling between the small-scale turbulent flow structures and the motion of the suspended particles. ¿ 2000 American Geophysical Union