Contents lists available at ScienceDirect Transportation Research Part D journal homepage: www.elsevier.com/locate/trd Real driving emissions of a scooter and a passenger car in Naples city Fabio Murena a , Maria Vittoria Prati b , Maria Antonietta Costagliola b, ⁎ a Department of Chemical, Materials and Production Engineering, University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy b Istituto Motori, National Research Council of Italy, Viale Marconi 4, 80125 Naples, Italy ARTICLE INFO Keywords: Real driving emissions Vehicle specific power Road gradient ABSTRACT The aim of the study was to investigate the real driving emissions of two vehicles widely used as private means of transport in Italian cities: a Euro 4 gasoline passenger car and a Euro 3 scooter. Exhaust emissions of two and four wheel vehicles were characterised over three urban routes in Naples. On-board measurement of CO, NOx, CO 2 and fuel consumption of the car was made with a Portable Emissions Measurement System (PEMS); exhaust emissions of NOx and fuel con- sumption of the scooter were measured in the laboratory, reproducing speed profiles acquired on the road on a chassis-dynamometer. In both cases, vehicle spatial position was acquired by Global Positioning System (GPS) at a frequency of 10 Hz. Real vehicle speed and acceleration together with road gradient were used to evaluate the specific power of the vehicle (VSP) and the results were modelled so as to correlate emissions with driving activities. Specific emissions and fuel consumption were also analysed as a function of road gradient. The most critical results for the car concerned NOx emissions which greatly exceeded the type-approval limit, and real driving of the scooter involved a significant increase in fuel consumption. For both vehicles, positive road gradient greatly influenced fuel demand, while NOx and CO emissions were considerably re- duced on downhill stretches. 1. Introduction Road transport is responsible for the emission of large quantities of pollutants and greenhouse gases (GHG). Recent studies of the European Environmental Agency estimate that in 2016 the road transport sector contributed almost 20% to total EU-28 CO 2 emissions, almost 10% to PM10, 39% to NOx and 19% to GHG (EEA 2018a, 2018b). These emissions have negative effects on local and global scales. Pollutants contribute significantly to health risks, especially in urban areas, while greenhouse gases contribute to climate change on a planetary scale. Since 1992, European legislation for vehicle type-approval stated standard limits for emission factors measured in the laboratory on vehicles under standard driving cycles. Although these limits become more and more stringent from Euro 1 to Euro 6 (coming into force in 2017), the discrepancies of laboratory measurements with real conditions can be significant, especially for species such as NOx and CO 2 (Zacharof et al., 2016; Kumar Pathak et al., 2016). Khan and Frey (2018) demonstrated that the differences between real-world emission rates and certification values of NOx and NMOG (Non Methane Organic Gas) depend on driving cycle, pollutant and vehicle group. On average, the real-world emission rates are 43% higher than type-approval limits. As of 1st September 2017, the European Commission introduced the Real Driving Emissions test procedure (RDE) for light-duty https://doi.org/10.1016/j.trd.2019.06.002 ⁎ Corresponding author. E-mail addresses: murena@unina.it (F. Murena), m.v.prati@im.cnr.it (M.V. Prati), m.a.costagliola@im.cnr.it (M.A. Costagliola). Transportation Research Part D 73 (2019) 46–55 1361-9209/ © 2019 Elsevier Ltd. All rights reserved. T