Use of portable emissions measurement system (PEMS) for the development and validation of passenger car emission factors

This paper discusses the development and validation of passenger car emission factors, using real world operation data. In total, six passenger cars of different technologies were studied. The tested vehicles were operated under various driving conditions and over two different routes in the region of Lombardia, Italy. These routes were specifically defined in order to provide a range of driving conditions, including urban, rural and highway driving. Tailpipe emissions and exhaust gas flows were measured on-board the vehicle, using a portable emissions measurement system (PEMS). In addition, all vehicles were tested over the European type-approval driving cycle (NEDC) with the same PEMS equipment. The testing of gasoline vehicles showed that emissions are well below the emission standards and do not raise any concern. However, the testing of diesel vehicles both under real-world driving conditions and over the NEDC brought to the surface important concerns regarding the actual NO_x emissions of modern diesel vehicles, since they seem to comply with the corresponding emission standard over the type-approval cycle, but they constantly exceed the specified limit when tested under real-world driving conditions. Results from real-world operation revealed that there is a significant deviation from the NO_x emission standard limit (especially for the newly introduced Euro 5 technology). These observations raise concerns regarding the actual NO_x emissions of modern vehicles and their impact on urban air-quality. The emission factors originally measured on the road are also compared to the corresponding COPERT average speed emission factors. In general, emissions of CO₂, THC and CO correlate fairly well with COPERT, for all vehicles. In the case of NO_x emissions, emission levels of the two tested Euro 5 diesel passenger cars are consistently higher in urban, rural, and highway driving compared to the corresponding COPERT emission factor. Thus, leading to the conclusion that more experimental data are necessary, especially for post-Euro 4 compliant diesel vehicles of different engine capacities particularly when it comes to NO_x emissions from diesel vehicles.