Soiling by Atmospheric Aerosols in an Urban Industrial Area

The gradual and progressive soiling of structures exposed to the atmosphere is commonplace. Wooden homes require painting every few years for aesthetic purposes as well as for preservation, while public buildings, houses of worship, and statuary require occasional exterior cleaning because of gradual soiling. Material soiling results from the deposition of atmospheric aerosols. Both wet and dry deposition occurs. Dry deposition mechanisms include gravitational settling, impaction, interception, diffusion, thermophoresis, and electrophoresis. The particle size and the orientation, exposure and roughness of the surface determine the dominant deposition mechanisms.