Dry deposition of particles to building surfaces and soiling

A separated turbulent flow around a cube with slightly rough surfaces of 3 x 3 cm area was produced to simulate particle deposition on edges or other small scale structures of building walls. Polydisperse soot particles with a mass mean diameter of 0.8 mu m produced by atomising a suspension of Indi a ink and monodisperse fluorescent 0.6 mu m latex spheres were used. The de position velocity of the soot particles was determined by measuring the cha nge in reflectance of the surrogate surfaces and the light absorption coeff icient of the aerosol. The deposited fluorescent spheres were counted by me ans of a fluorescence microscope. Deposition velocities of the fluorescent spheres used in outdoor experiments were equal to deposition velocities of the soot particles used in a small wind tunnel. The density of the deposit was different on each side of the cube and also inhomogeneously distributed on each individual surface. The highest deposition was always found on the edges of the cube. This peculiar deposition pattern could be explained by the characteristics of the turbulent flow field around the surfaces which w as measured by laser Doppler anemometry. Modelled soiling constants calcula ted with the help of the measured deposition velocities were up to a factor of 10 higher than values obtained for a flat plate in a simple boundary la yer flow. (C) 1999 Elsevier Science B.V. All rights reserved.