Hydrocarbons, CO, NOx, NH3, N2O, CO2 and particulate matter emissions affect air quality, global warming and human health. Transport sector is an important source of these pollutants and high pollution episodes are often experienced during the cold season. However, EU vehicle emissions regulation at cold ambient temperature only addresses hydrocarbons and CO vehicular emissions. For that reason, we have studied the impact that cold ambient temperatures have on Euro 6 diesel and spark ignition (including: gasoline, ethanol flex-fuel and hybrid vehicles) vehicle emissions using the World-harmonized Light-duty Test Cycle (WLTC) at -7 °C and 23 °C. Results indicate that when facing the WLTC at 23 °C the tested vehicles present emissions below the values set for type approval of Euro 6 vehicles (still using NEDC), with the exception of NOx emissions from diesel vehicles that were 2.3-6 times higher than Euro 6 standards. However, emissions disproportionally increased when vehicles were tested at cold ambient temperature (-7 °C). High solid particle number (SPN) emissions (>1 × 1011 # km-1) were measured from gasoline direct injection (GDI) vehicles and gasoline port fuel injection vehicles. However, only diesel and GDI SPN emissions are currently regulated. Results show the need for a new, technology independent, procedure that enables the authorities to assess pollutant emissions from vehicles at cold ambient temperatures. Harmful pollutant emissions from spark ignition and diesel vehicles are strongly and negatively affected by cold ambient temperatures. Only hydrocarbon, CO emissions are currently regulated at cold temperature. Therefore, it is of great importance to revise current EU winter vehicle emissions regulation.

Passenger cars are an important source of air pollution, especially in urban areas. Recently, real-driving emissions (RDE) test procedures have been introduced in the EU aiming to evaluate nitrogen oxides (NOx) and particulate number (PN) emissions from passenger cars during on-road operation. Although RDE accounts for a large variety of real-world driving, it excludes certain driving situations by setting boundary conditions (e.g., in relation to altitude, temperature or dynamic driving). The present work investigates the on-road emissions of NOx, NO2, CO, particle number (PN) and CO2 from a fleet of 19 Euro 6b, 6c and 6d-TEMP vehicles, including diesel, gasoline (GDI and PFI) and compressed natural gas (CNG) vehicles. The vehicles were tested under different on-road driving conditions outside boundaries. These included 'baseline' tests, but also testing conditions beyond the RDE boundary conditions to investigate the performance of the emissions control devices in demanding situations. Consistently low average emission rates of PN and CO were measured from all diesel vehicles tested under most conditions. Moreover, the tested Euro 6d-TEMP and Euro 6c diesel vehicles met the NOx emission limits applicable to Euro 6d-TEMP diesel vehicles during RDE tests (168 mg/km). The Euro 6b GDI vehicle equipped with a gasoline particulate filter (GPF) presented PN emissions < 6 × 1011 #/km. These results, in contrast with previous on-road measurements from earlier Euro 6 vehicles, indicate more efficient emission control technologies are currently being used in diesel and gasoline vehicles. At the same time, the results suggest that particular attention should be given to CO and PN emissions of certain types of vehicles when driven under dynamic conditions, and possibly additional work is necessary. In particular, the emissions of CO (measured in this study during the regulated RDE test, but without an emission limit associated to it) or PN from PFI vehicles (presently not covered by the Euro 6 standard) showed elevated results in some occasions. Emissions of CO were up to 7.5 times higher when the more dynamic tests were conducted and the highest PN emissions were measured from a PFI gasoline vehicle during dynamic driving. Although based on a limited sample of cars, our work points to the relevance of a technology- and fuel-neutral approach to vehicle emission standards, whereby all vehicles must comply with the same emission limits for all pollutants.

Background: Road transport is an important contributor to the European Union’s total greenhouse gas emissions. This study aims at summarizing methane (CH₄) and nitrous oxide (N₂O) exhaust emissions from L-category, light-duty and heavy-duty vehicles in the European Union. The assessment is based on measurements carried out in the Vehicle Emission Laboratory of the Joint Research Centre between 2009 and 2019. The exhaust chemical composition from a fleet of 38 L-category vehicles Euro 1 to Euro 4 (2- and 3-wheelers, small quadricycles such as quads and minicars), 63 light-duty vehicles from Euro 5b to Euro 6d-TEMP (passenger cars, including hybrid vehicles), and 27 light commercial and heavy-duty vehicles from pre-Euro I to Euro VI (including lorries, buses and garbage trucks) was analyzed by Fourier-transform infrared spectroscopy. Results: CH₄ emission factors monitored were from 1 to 234 mg/km for L-category vehicles (mean: 39 mg/km), from 0.1 to 40 mg/km for light-duty vehicles (mean: 7 mg/km), and from non-detectable to 320 mg/km for heavy-duty vehicles (mean: 19 mg/km). N₂O emission factors monitored were from non-detectable to 5 mg/km for L-category vehicles (mean: 1 mg/km), from non-detectable to 40 mg/km for light-duty vehicles (mean: 7 mg/km), and from non-detectable to 118 mg/km for heavy-duty vehicles (mean: 19 mg/km). According to the 100-year Global Warming Potential of these greenhouse gases, these emissions corresponded to a range from negligible up to 9 g/km of CO₂-equivalent for CH₄ and from negligible up to 32 g/km of CO₂-equivalent for N₂O. Conclusions: The higher contributors of CH₄ were the two-stroke mopeds included in the L-category vehicles, while the higher emissions of N₂O were found in the modern (Euro 5–6 or Euro V–VI) diesel light- and heavy-duty vehicles. Among them, vehicles complying with Euro 6 and Euro VI standard were associated to higher N₂O emissions compared to those associated to Euro 5 and pre-Euro IV standards, which could be attributed to the introduction of the after-treatment systems designed to fulfill more stringent NOx standards. These updated emission factors and unique on its kind database represent a source of information for legislators and modelers to better assess the greenhouse gas emission reduction in the EU transport sector.

The transport sector is one of the main sources air pollutants. Different exhaust after-treatment systems have been implemented over the years to control the emissions of criteria pollutants. However, while reducing the emissions of the target compounds these systems can lead to the emissions of other pollutants and/or greenhouse gases such as NH₃ or N₂O. Following the implementation of the Real Driving Emissions (RDE) test procedure in the EU, vehicles have been equipped with more complex after-treatment configurations. The impact that these technologies may have on the emissions of non-regulated pollutants during real-world driving have not been evaluated until now. In the current study we present the on-road emissions of a series of non-regulated pollutants, including NH₃, N₂O, CH₄ and HCHO, measured with a portable FTIR from a series of Euro 6d, Euro 6c and Euro 6d-TEMP, gasoline diesel and compressed natural gas (CNG) vehicles during real-world testing. The obtained results show that it is possible to measure N₂O, NH₃, CH₄ and HCHO during on-road operation. The results also highlight the importance of the measurement of the emissions of these pollutants during real-world driving, as the emissions of NH₃ (a particulate matter precursor) and those of N₂O and CH₄ (green-house gases) can be high from some vehicle technologies. NH₃ emissions were up to 49 mg/km for gasoline passenger cars, up to 69 mg/km for the CNG light-commercial vehicle and up to 17 mg/km a diesel passenger car equipped with a selective catalytic reduction system (SCR). On the other hand, N₂O and CH₄ emissions accounted for up to 9.8 g CO₂ eqv/km for a diesel passenger car equipped with a combination of diesel oxidation catalysts (DOC), lean NO_x traps (LNT), SCR and possibly an ammonia slip catalyst ASC.

Tailpipe emissions of a pool of 13 Euro 6b light-duty vehicles (eight diesel and five gasoline-powered) were measured over an extensive experimental campaign that included laboratory (chassis dynamometer), and on-road tests (using a portable emissions measurement system). The New European Driving Cycle (NEDC) and the Worldwide harmonised Light-duty vehicles Test Cycle (WLTC) were driven in the laboratory following standard and extended testing procedures (such as low temperatures, use of auxiliaries, modified speed trace). On-road tests were conducted in real traffic conditions, within and outside the boundary conditions of the regulated European Real-Driving Emissions (RDE) test. Nitrogen oxides (NO_X), particle number (PN), carbon monoxide (CO), total hydrocarbons (HC), and carbon dioxide (CO₂) emission factors were developed considering the whole cycles, their sub-cycles, and the first 300 s of each test to assess the cold start effect. Despite complying with the NEDC type approval NO_X limit, diesel vehicles emitted, on average, over the WLTC and the RDE 2.1 and 6.7 times more than the standard limit, respectively. Diesel vehicles equipped with only a Lean NO_X trap (LNT) averaged six and two times more emissions over the WLTC and the RDE, respectively, than diesel vehicles equipped with a selective catalytic reduction (SCR) catalyst. Gasoline vehicles with direct injection (GDI) emitted eight times more NO_X than those with port fuel injection (PFI) on RDE tests. Large NO_X emissions on the urban section were also recorded for GDIs (122 mg/km). Diesel particle filters were mounted on all diesel vehicles, resulting in low particle number emission (~10¹⁰ #/km) over all testing conditions including low temperature and high dynamicity. GDIs (~10¹² #/km) and PFIs (~10¹¹ #/km) had PN emissions that were, on average, two and one order of magnitude higher than for diesel vehicles, respectively, with significant contribution from the cold start. PFIs yielded high CO emission factors under high load operation reaching on average 2.2 g/km and 3.8 g/km on WLTC extra-high and RDE motorway, respectively. The average on-road CO₂ emissions were ~33% and 41% higher than the declared CO₂ emissions at type-approval for diesel and gasoline vehicles, respectively. The use of auxiliaries (AC and lights on) over the NEDC led to an increase of ~20% of CO₂ emissions for both diesel and gasoline vehicles. Results for NO_X, CO and CO₂ were used to derive average on-road emission factors that are in good agreement with the emission factors proposed by the EMEP/EEA guidebook.

Plug-in hybrid electrical vehicles (PHEVs) are generally considered to be a cleaner alternative to conventional passenger cars. However, there is still very limited information available regarding criteria pollutant emissions from these vehicles. This paper shows, for the first time, the emissions of criteria pollutants, unregulated pollutants, and CO₂ and also electric range from two very different PHEVs, one Euro 6 parallel plug-in hybrid and one range-extended battery electric vehicle (BEVx), applying the new world harmonized light-duty test procedure at ambient temperatures equal to 23 and −7 °C. The impact of using a cabin air heating system on vehicle electric range and emissions at cold temperature has also been studied. Cold ambient temperatures and, to a larger extent, the use of heating systems have been shown to lead to a pronounced negative impact on emissions and shorter electric ranges. Results also show that modern PHEVs can emit similar, or even higher, levels of pollutants (e.g., particle number) as Euro 6 conventional gasoline and diesel vehicles.