Dust deposition and the soiling of glossy surfaces

Measurements of changes in reflectance caused by dust deposits on a glossy surface using a standard gloss-meter are described. A microscope slide exposed at a roadside and a rooftop site in central London was used as a convenient collector surface to simulate the soiling by dust of such glossy surfaces as glass, polished metal and plastic, automotive finishes and gloss paint. Measured reductions in gloss made over a number of weeks showed mean values between 1.4% and 1.9% per 6 h. Measurements made at the roadside showed an approximately linear relationship between gloss and percentage area of the slide covered by dust, as measured by a Magiscan II image analyser set up to measure particles greater than 5 microm in diameter. No such relationship was observed for measurements made at the rooftop site.