The development of diesel particle size distributions in an enclosed chamber is investigated for particles with midpoint diameters ranging from 15.9 to 673.2 nm. All measurements were carried out in a 0.2 m(3) chamber under ambient pressure and ambient temperature. The particle concentration decreases steadily over time, while the geometric mean diameter shifts towards larger diameters. (C) 2004 Elsevier Ltd. All rights reserved.