The main source to air pollution in densely built-up areas such as cities is the road traffic. Traffic is increasing and more people are being exposed to its air pollution emissions when urbanization is spreading. A densification is taking place in present settlement and the vicinity that is left to build on is often situated in close connection to roads with heavy traffic. The legislation purpose is to protect health and environment aiming on the most health hazardous air pollutants; particles (PM10) and ozone (O3). The main purpose of his thesis is to compare development in PM10- and NOx trends and contents on nine European streets and to discuss the differences in terms of meteorology, traffic and emissions. The purpose of the thesis is also to give a survey of health effects and current legislation on air pollution.