Particle-Size-Dependent Analysis of the Impact of Temperature, Humidity, and Tilt Angle on Soiling

Natural soiling—the deposition of dust onto surfaces—is a very complex problem and influenced by different factors, such as weather conditions, dust type, or surface properties. To investigate the individual impact of various factors and parameters, laboratory and outdoor soiling tests were performed for uncoated glass samples and glass samples with an antisoiling coating. For this, an advanced experimental setup was used operating at controlled environmental conditions. A detailed microscopic investigation with particle size analysis was performed to better understand the underlying physics of soiling effects and its influencing parameters, including relative humidity, surface temperature, tilt angle, and properties of the sample surface (i.e., glass coatings). Various effects were identified, which must not be neglected for correct interpretation of soiling test results. The article shows that particle rebound, natural convection, thermophoresis, capillary condensation, and adhesion properties of the surface have a substantial impact on soiling.