Velocity-dependent emission factors of benzene, toluene and C2-benzenes of a passenger car equipped with and without a regulated 3-way catalyst

Time-resolved chemical ionization mass spectrometry (CI-MS) has been used to investigate the velocity-dependent emission factors for benzene, toluene, the C2-benzenes (xylenes and ethyl benzene) and nitrogen monoxide of a gasoline-driven passenger car (1.4 l, model year 1995) driven with or without catalytic exhaust gas treatment. A set of seven different driving cycles – including the European Driving Cycle (EDC), the US Urban (FTP 75) and the Highway driving cycles – with a total driving time of 12,000 s have been studied. From the obtained emission data, two sets of 15,300 and 17,200 data points which represent transient driving in the velocity range of 0–150 km h−1 and in an acceleration window of −2–3 m s−2 were explored to gain velocity-dependent emission factors. The passenger car, equipped with a regulated rhodium–platinum based three-way catalyst, showed optimal conversion efficiency (>95%) for benzene in the velocity range of 60–120 km h−1. The conversion of benzene was reduced (<80%) when driving below 50 km h−1 and the BTXE emissions significantly increased when driven at higher speed and engine load (>130 km h−1). Whereas the conversion efficiency for the class of C2-benzenes was reduced to 10%, no net conversion could be found for toluene and benzene when driven above 130 km h−1. In contrast, the benzene and toluene emissions exceeded those of the untreated exhaust gas in the velocity range of 130–150 km h−1 by 50–92% and by 10–34%, respectively. Thus, benzene and toluene were formed across the examined three-way catalyst if the engine is operated for an extended time in a fuel-rich mode (lambda<1).