Traffic-related air pollution is still one of the most pressing problems in urban areas. Evidence of the adverse health effects of fine particulate matter is continuously emerging and it is alarming that most of the traffic-related emissions are in the fine particulates range (< PM2.5). Human exposure to increased pollutant concentrations in densely populated urban areas is high. The improvement of air quality is therefore imperative. Air quality limit values, which are aimed at protecting public health, are frequently exceeded especially in streets and other urban hotspots.