The influence of gasoline benzene and aromatics content on benzene exhaust emissions from non-catalyst and catalyst equipped cars. A study of European data

Report no. 96/51: An analysis of data on the effect of gasoline benzene and aromatics contents on exhaust benzene emissions has been conducted. It was based on data from CONCAWE member companies and an Italian industry programme, and included the results of emission tests on 21 conventional non-catalyst and 34 catalyst cars. Although none of these programmes was specifically aimed at investigating the combined effects of gasoline benzene and aromatics content on benzene exhaust emissions, the combination of data from the individual programmes allowed some insight into these relationships.

Earlier programmes conducted with non-catalyst cars - using the ECE-15 test cycle - demonstrated that the main effect on benzene exhaust emissions derived from the benzene content of the gasoline employed. However, higher aromatics also influenced benzene exhaust emissions, albeit to a lesser extent. The effect of benzene in those earlier programmes was about twelve times higher than that of higher aromatics. Analysis of new emissions data over the combined ECE15+EUDC test cycle indicated that similar relationships existed for both non-catalyst and catalyst cars.If benzene emissions are expressed as a percentage of total hydrocarbons emitted, then the effect of gasoline benzene content and other aromatics varies between vehicle type. More specifically, the influence of fuel benzene content was found to be over 18 times greater than that of non-benzene aromatics for non-catalyst cars.

For catalyst equipped cars, the effect of benzene content was 10 times greater than that of other aromatics. Moreover, benzene exhaust emissions from catalyst cars were substantially lower. On average, emissions were reduced by around 85%, demonstrating the efficient control provided by the catalysts employed.It has also been demonstrated that the regression equations developed predict the trends and magnitude of the benzene exhaust emissions observed over the modified ECE (11 s)+EUDC cycle, as used in the EPEFE programme and the 1994 CONCAWE gasoline study. This cycle employs a shorter idle period at the start of the test and collects exhaust emissions immediately from cranking the engine.