Factors affecting Dirt Pick up of Traffic Paints in Areas with Different Characteristics: Tehran Roads as a Case Study

In recent years, the dirt pick up problem and loss quality of brightness of traffic marking paints have widely attracted municipal authorities’ attention. Reflective traffic paints and road marking are some of the most technologically advanced pieces of safety and traffic signs that should be there to have safe streets [1-5]. The most important problem regarding with today’s traffic marking paints is their low resistance to dirt pickup. The dirt pick up can occur in two ways: migration of the stains from bottom substrate to paint surface and pollutant deposition on paint surfaces [6]. In the first case of the dirt type, low quality of asphalt make dirt migrate to the surface of the paint but the later happens when thousands of different solid and liquid particles suspended in the atmosphere is settled on the surface by dry or wet atmospheric deposition. The surficial dirt is made up of many components, including elemental or black carbon (BC) and organic carbon (OC) compounds, sulfate (SO4), nitrate (NO3-), trace metals, crustal material (i.e. soil particles) and sea salt [7]. Dirt with amphiphilic characteristics adheres abnormally to painted surfaces (Figure 1). Pollutants emitted from different sources comes in a wide range of sizes and includes particulate matter with diameter less than or equal to 10 μm (PM10), fine particulate matter with diameter less than or equal to 2.5 μm (PM2.5), ultrafine particulate matter with diameter less than or equal to 0.1 μm (PM0.1), and lastly nanoparticles pollutants with diameter less than or equal to 0.05 μm (PM0.05).