Time-resolved Chemical Ionisation Mass Spectrometry (CI-MS) has been used to investigate the benzene emission profiles in automotive exhaust during transient engine operation with a time resolution of one second. Representative gasoline driven passenger cars and light duty vehicles with model years 1991 to 1996 have been selected from the Swiss car fleet and were measured on the chassis dynamometer at the Swiss Federal Laboratories for Materials Testing and Research (EMPA). The benzene emission characteristics of a fleet of 20 passenger cars (1.3 -5.2 l), 8 light duty vehicles (2.0-2.4 l) and one conventional vehicle (1.4 l) have been determined. A set of seven different driving cycles, including the European Driving Cycle (ECD), the US Urban (FTP 75), the Highway and four additional driving cycles, with a total driving time of 12.000 seconds have been investigated by CI-MS. Velocity dependent emission factors for the individual vehicles as well as for the different vehicle classes were determined by a statistical analysis of the corresponding emission data. From such reference data sets weighted benzene emission factors for car fleets with variable proportions of the studied vehicle categories can be derived. (A)
Abstract