AMBIENT AIR CONCENTRATIONS OF POLLUTANTS AT TRAFFIC-RELATED SITES IN URBAN AREAS OF NORTH-RHINE-WESTPHALIA, GERMANY

The North Rhine-Westphalia State Centre for Air Quality Control and No ise Abatement (LIS) operates one of the largest and most extensive mon itoring networks for air quality control in Europe. It comprises the t elemetric air pollution monitoring network TEMES, with seventy-six sta tionary stations and eight mobile monitoring stations. Many of these s tations are affected by automobile traffic on highways and in urban st reets. At present, automated measurements are taken of sulfur dioxide, nitric oxide, nitrogen dioxide, carbon monoxide, suspended particulat es, ozone and seven meteorological parameters. At the same sites, susp ended particulates are collected with semi-automated instruments and a nalysed for heavy metals and polycyclic aromatic hydrocarbons. About t hirty-five different volatile hydrocarbons and chlorinated hydrocarbon s are determined in random samples taken at the TEMES stations. In rec ent years diesel exhaust has become more and more important since it w as included in the list of carcinogenic substances in Germany. Consequ ently, the LIS been measurements of diesel soot, mostly at sites expos ed to traffic. For some air pollutants, such as nitrogen oxides, carbo n monoxide and hydrocarbons, road traffic is the most important emissi on source. This was confirmed by extensive monitoring performed by the LIS, which revealed that the ambient air concentrations of these comp ounds at sites exposed to traffic are considerably higher than at othe r urban measuring points. For example, at a very busy junction in Duss eldorf, the mean concentrations of carbon monoxide and nitrogen oxide are more than three and rive times higher than the averages computed f rom data from all other stations in the urban, industrialised and dens ely populated Rhine-Ruhr area that are not directly affected by road t raffic. For lead and polycyclic aromatic hydrocarbons the differences are less significant but still discernible. The annual mean concentrat ion of carcinogenic benzene at the Dusseldorf station (reaching 30 mug /m3) is six times higher than the overall level in the Rhine-Ruhr area . The carcinogenic risk at sites exposed to traffic, however, is prima rily caused by diesel engine emissions (diesel soot).