Particle and deposit characteristics were studied with a new laboratory-scale deposition-corrosion apparatus designed to simulate the particle formation and deposition in large-scale diesel engines. Synthetic ash particles containing V, Ni, and Na are generated with an ultrasonic nebuliser. Total particle mass concentrations varied from 463 to 1739 mg/N m(3) and highest concentrations were reached with SO2(g) feed and cold dilution. Mass size distributions at the size range of 0.01-15 mum (aerodynamic size) were unimodal at 1.4 mum. Particle morphology changed dramatically from 1 to 5 mum sized solid particles without SO2(g) feed into flat wet "pools" with SO2(g) feed. It seemed that condensing sulphuric acid had dissolved the particles. Small 70-90 nm spherical particles were also observed with SO2(g) feed. On the other hand, hardly any S was found in the deposits, which indicated that S as SO2(g)/SO3(g) was transported through the deposit pile into the base material. (C) 2004 Elsevier B.V. All rights reserved.