Ambient air concentrations of pollutants at traffic-related sites in urban areas of North Rhine-Westphalia, Germany

Abstract

The North Rhine-Westphalia State Centre for Air Quality Control and Noise Abatement (LIS) operates one of the largest and most extensive monitoring networks for air quality control in Europe. It comprises the telemetric air pollution monitoring network TEMES, with seventy-six stationary stations and eight mobile monitoring stations. Many of these stations are affected by automobile traffic on highways and in urban streets. At present, automated measurements are taken of sulfur dioxide, nitric oxide, nitrogen dioxide, carbon monoxide, suspended particulates, ozone and seven meteorological parameters. At the same sites, suspended particulates are collected with semi-automated instruments and analysed for heavy metals and polycyclic aromatic hydrocarbons. About thirty-five different volatile hydrocarbons and chlorinated hydrocarbons are determined in random samples taken at the TEMES stations. In recent years diesel exhaust has become more and more important since it was included in the list of carcinogenic substances in Germany. Consequently, the LIS began measurements of diesel soot, mostly at sites exposed to traffic. For some air pollutants, such as nitrogen oxides, carbon monoxide and hydrocarbons, road traffic is the most important emission source. This was confirmed by extensive monitoring performed by the LIS, which revealed that the ambient air concentrations of these compounds at sites exposed to traffic are considerably higher than at other urban measuring points. For example, at a very busy junction in Düsseldorf, the mean concentrations of carbon monoxide and nitrogen oxide are more than three and five times higher than the averages computed from data from all other stations in the urban, industrialised and densely populated Rhine-Ruhr area that are not directly affected by road traffic. For lead and polycyclic aromatic hydrocarbons the differences are less significant but still discernible. The annual mean concentration of carcinogenic benzene at the Düsseldorf station (reaching 30 μg/m 3) is six times higher than the overall level in the Rhine-Ruhr area. The carcinogenic risk at sites exposed to traffic, however, is primarily caused by diesel engine emissions (diesel soot).