Besides regulated components VW's research program in the field of characterization of diesel emissions comprises a detailed analysis of the particulates and a comprehensive study of a number of unregulated gaseous compounds. The following chemical compounds and classes of compounds are measured: particulates, traces of metals, major elements, sulfates, sulfur dioxide, hydrogen sulfide, hydrogen cyanide, aldehydes, ammonia phenols, individual hydrocarbons, and odor (DOAS). The test fleet of this investigation included a number of VW and Audi cars equipped with 4-, and 5-cylinder diesel engines (naturally aspirated and turbocharged). All measurements were performed on a chassis dynamometer in accordance with the specification of the known US-test-procedures: Federal Test Procedure, Sulfate Emission Test, Fuel Economy Test. For sampling, in principle, the dilution tunnel technique was used combined with an automatically working collection system. This micro-processor controlled system involves 13 individual sample lines, 8 for gaseous and 5 for particulate components.For mileage accumulation effects one vehicle was operated over 50,000 mi under normal in-use conditions. In order to study influences of malfunction two abnormal engine conditions were selected.Estimation of a relative importance of the data was carried out using the threshold limit values as the criteria.