Understanding particle deposition onto rough surfaces is important for many engineering and environmental applications. An experimental system was designed for the study of aerosol deposition on regular arrays of uniform elements (in the form of discrete protrusions) in a turbulent ventilation duct flow using monodisperse tracer small particles, in the range 0.7-7.1 mum. The Reynolds number for the test conditions was 44,000 in the 150 mm square duct. The roughness elements were arranged at two different orientations with respect to the airflow direction and the aerosol deposition velocity and pressure drop were measured for both orientations. Compared to earlier measurements in the same duct system involving smooth or ribbed surfaces, a significant increase in deposition velocity onto the regular roughness elements is observed. In addition, the associated pressure loss penalty is lower than in the presence of the roughness elements than in the presence of the ribbed surfaces. This may be attributable to the small dimensionless roughness height of the elements, which results only in a moderate distortion of the how structure near the surfaces. (C) 2000 Elsevier Science Ltd. All rights reserved.