A computer-automated optical microscope combined with a line-sensing camera was used to capture the entire range of a particle deposit downstream of an individual acceleration nozzle in a hi-volume Andersen sampler. To investigate the particle bounce and reentrainment, particles collected on collocated greased and non-greased Teflon plates on the inlet stage (d(a) > 7 mum) were observed by an automated particle counting, locating and sizing method. The result confirmed reproducible collection characteristics among nozzles even though application of the grease increased collection efficiency and altered the size distribution of collected particles to the larger side. In these experiments, assuming spherical particles with uniform density, approximately 65% of particle mass and 50% by number were lost from non-greased plates at 54% RH, while 45% by mass and 25% by number were underestimated at 84% RH. The spatial investigation showed that particles were densely deposited around the center of deposition on greased plates while on non-greased plates they were dispersedly distributed. Particle dispersions on the smooth impaction plate were due to bounce and/or reentrainment of small particles especially with d(PA) < 10 mum. (C) 2002 Elsevier Science Ltd. All rights reserved.