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 C-2-benzenes (xylenes and ethyl benzene) and nitrogen monoxide of a gasoline-driven passenger car (1.41, 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 C-2-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). (C) 2000 Elsevier Science Ltd. All rights reserved.