Regulated and Non-Regulated Emissions from Euro 6 Diesel, Gasoline and CNG Vehicles under Real-World Driving Conditions

Regulated and unregulated emissions from Euro VI Diesel and CNG heavy-duty vehicles

This study compares emissions from Euro VI-D Diesel and CNG buses across temperatures from -7 °C to 35 °C. Pollutants including NOx, THC, CH4, CO, NH3, N2O, HCHO, Solid Particle Number larger than 23 nm (SPN23) and larger than 10 nm (SPN10) were measured. Both buses complied with Euro VI-D but exceeded European Commission's proposed Euro 7 limits, notably for NOx and SPN10. The CNG bus also surpassed NH3, CO, and CH4 limits, while the Diesel exceeded N2O limits. High NH3 emissions were observed from CNG (up to 0.320 g/kWh), with Diesel reporting lower levels (up to 0.021 g/kWh). HCHO emission from both vehicles were very low. SPN23 was under limits, but SPN10 exceeded Euro 7 limits at cold start tests. CNG's CH4 and N2O emissions constituted up to 4.6% and 3.5% of CO2 equivalent, respectively. Diesel bus showed negligible CH4 but N2O emissions represented up to 37% of CO2 equivalent.

Forecasting CO2 emissions of fuel vehicles for an ecological world using ensemble learning, machine learning, and deep learning models

Background

The continuous increase in carbon dioxide (CO2) emissions from fuel vehicles generates a greenhouse effect in the atmosphere, which has a negative impact on global warming and climate change and raises serious concerns about environmental sustainability. Therefore, research on estimating and reducing vehicle CO2 emissions is crucial in promoting environmental sustainability and reducing greenhouse gas emissions in the atmosphere.

Methods

This study performed a comparative regression analysis using 18 different regression algorithms based on machine learning, ensemble learning, and deep learning paradigms to evaluate and predict CO2 emissions from fuel vehicles. The performance of each algorithm was evaluated using metrics including R2, Adjusted R2, root mean square error (RMSE), and runtime.

Results

The findings revealed that ensemble learning methods have higher prediction accuracy and lower error rates. Ensemble learning algorithms that included Extreme Gradient Boosting (XGB), Random Forest, and Light Gradient-Boosting Machine (LGBM) demonstrated high R2 and low RMSE values. As a result, these ensemble learning-based algorithms were discovered to be the most effective methods of predicting CO2 emissions. Although deep learning models with complex structures, such as the convolutional neural network (CNN), deep neural network (DNN) and gated recurrent unit (GRU), achieved high R2 values, it was discovered that they take longer to train and require more computational resources. The methodology and findings of our research provide a number of important implications for the different stakeholders striving for environmental sustainability and an ecological world.

Influencing factors on ammonia emissions from gasoline vehicles: A systematic review and meta-analysis

Ammonia, a significant precursor for secondary inorganic aerosols, plays a pivotal role in new particle formation. Inventories and source apportionment studies have identified vehicular exhaust as a primary source of atmospheric ammonia in urban regions. Existing research on the factors influencing ammonia emissions from gasoline vehicles exhibits substantial inconsistencies in both test results and analyses. The lack of a uniform pattern in ammonia emissions across different standard vehicles and the significant overlap in test results across diverse operational conditions highlight the complexities in this field of study. While individual results can be interpreted through a mechanistic lens, disparate studies often lack a common explanatory framework. To address this gap, our study leverages the robust and comprehensive approach of meta-analysis to reconcile these inconsistencies and provide a more precise understanding of the factors influencing ammonia emissions from gasoline vehicles. A large number (N = 537) of ammonia emission factors were extracted after screening >1628 publications. The combined ammonia emission factor was 23.57 ± 24.94 mg/km. Emission standards, engine type, ambient temperatures, mileage, vehicle speed, and engine displacement have a significant impact on ammonia emission factors, explaining the ammonia emission factor by up to 50.63 %, with speed being the most significant factor. All these factors are attributed to the interplay of catalyst properties, lambda, and residence time (space velocity). In the current fleet, ammonia emission control is relatively insufficient under low-speed and ultra-high speed, low temperature, and ultra-high mileage conditions. Since ammonia emission factors do not monotonically decrease with the upgrading of motor vehicle emission standards, it is called for the addition of ammonia emission factors indicators in motor vehicle emission standards, and stipulation of targeted testing procedures and testing instruments.

Vehicular Ammonia Emissions Significantly Contribute to Urban PM2.5 Pollution in Two Chinese Megacities

Ammonia (NH₃) plays a vital role in the formation of fine particulate matter (PM_2.5). Prior studies have primarily focused on the control of agricultural NH₃ emissions, the dominant source of anthropogenic NH₃ emissions. The air quality impact from vehicular NH₃ emissions, which could be particularly important in urban areas, has not been adequately evaluated. We developed high-resolution vehicular NH₃ emission inventories for Beijing and Shanghai based on detailed link-level traffic profiles and conducted atmospheric simulations of ambient PM_2.5 concentrations contributed by vehicular NH₃ emissions. We found that vehicular NH₃ emissions shared high proportions among total anthropogenic NH₃ emissions in the urban areas of Beijing (86%) and Shanghai (45%), where vehicular NH₃ was primarily emitted by gasoline vehicles. Local vehicular NH₃ emissions could be responsible for approximately 3% of urban PM_2.5 concentrations during wintertime, and the contributions could be much higher during polluted periods (∼3 μg m^-3). We also showed that controlling vehicular NH₃ emissions will be effective and feasible to alleviate urban PM_2.5 pollution for megacities in the near future.

Sources identification of ammonium in PM2.5 during monsoon season in Dhaka, Bangladesh

Ammonia (NH₃) is taken up by fine particulate matter (PM_2.5), and there are concerns about its impact on the environment and health. The source of NH₃, which was thought to be of agricultural sources, has recently been suspected to be non-agricultural sources in urban areas. Here, we collected PM_2.5 during the monsoon season in Dhaka, Bangladesh, the most polluted city in the world, and analyzed the δ¹⁵N-NH₄⁺ in PM_2.5. As the result, the δ¹⁵N-NH₄⁺ ranged from 9.2 ‰ to 34.4 ‰ (average: 20.7 ± 4.8 ‰), the highest of any of the averaged values annual reported in previous researches. In order to perform source analysis, the NH₃ concentrations were estimated using the thermodynamic model ISORROPIA-II. The estimated concentration of NH₃ gas averaged 40.8 μg/m³ (3.0-154.6 μg/m³). The contributions calculated with the mixing model to the δ¹⁵N-NH₄⁺ values in PM_2.5 in Dhaka, Bangladesh averaged 25.3 ± 14 %, 22.8 ± 10 %, 26.5 ± 15 %, and 25.4 ± 10 % for waste, fertilizer, NH₃ slip, and fossil fuel combustion, respectively. Non-agricultural sources (NH₃ slip, and fossil fuel combustion) accounted for almost half (51.9 %) of the contributions. In addition, the several validation tests of the isotope mixing model were also performed. For validating the uncorrected and corrected source data for δ¹⁵N-NH₃, the contribution of non-agricultural sources with uncorrected source data would have been very high (>80 %), much higher than the corrected source data.

Investigation of the evolution of Pd-Pt supported on ceria for dry and wet methane oxidation

Efficiently treating methane emissions in transportation remains a challenge. Here, we investigate palladium and platinum mono- and bimetallic ceria-supported catalysts synthesized by mechanical milling and by traditional impregnation for methane total oxidation under dry and wet conditions, reproducing those present in the exhaust of natural gas vehicles. By applying a toolkit of in situ synchrotron techniques (X-ray diffraction, X-ray absorption and ambient pressure photoelectron spectroscopies), together with transmission electron microscopy, we show that the synthesis method greatly influences the interaction and structure at the nanoscale. Our results reveal that the components of milled catalysts have a higher ability to transform metallic Pd into Pd oxide species strongly interacting with the support, and achieve a modulated PdO/Pd ratio than traditionally-synthesized catalysts. We demonstrate that the unique structures attained by milling are key for the catalytic activity and correlate with higher methane conversion and longer stability in the wet feed.

Road Traffic and Its Influence on Urban Ammonia Concentrations (France)

Ammonia (NH3) is an unregulated atmospheric gaseous pollutant in ambient air, involved in the formation of fine particles. Ammonia is therefore a major precursor of particulate matter (PM), the health effects of which have been widely demonstrated. NH3 emissions are clearly dominated by the agricultural sector (livestock and fertilizers), but other sources may also be important and less studied, such as road traffic with the increased use of catalytic converters in vehicles. This study is based on a long-term real-time measurements campaign (December 2019–September 2021) on two urban sites: a background site and a roadside site in the same agglomeration in France. The study of historical measurements at the background site clearly demonstrated the dominance of agriculture on the ammonia concentrations. This influence was also observed at both sites during the measurement campaign. The annual and monthly averages obtained in the study were similar to previous ones, with concentrations between 1–10 µg/m3 at both sites, indicating lower levels than previous studies for the roadside site. The ammonia levels measured during the campaign at the traffic site were significantly higher than those measured at the background site, highlighting the road traffic influence on ammonia in urban area. The biomass burning influence also seemed to be observed during this long measurement campaign at the agglomeration scale. The influences of road traffic and biomass burning on ammonia concentration remain small compared to agriculture.

Emissions of Euro 6 Mono- and Bi-Fuel Gas Vehicles

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives in Europe. Most studies on emissions factors are based on old technology CNG and LPG fueled vehicles. Furthermore, there are not many data at low ambient temperatures, on-road driving, or unregulated pollutants, such as ammonia (NH3). In this study we measured the emissions of one Euro 6b CNG light commercial vehicle, one Euro 6b and one Euro 6d-Temp bi-fuel LPG passenger car, one Euro 6d-Temp bi-fuel CNG passenger car, and four Euro 6d-Temp CNG passenger cars. Tests included on-road testing and worldwide harmonized light vehicles test cycles (WLTC) in the laboratory with cold and hot engine, at 23 °C and −7 °C. The results showed 10–23% CO2 savings in gas modality compared to gasoline, lower CO and particle number emissions, and relatively similar total and non-methane hydrocarbons and NOx emissions. The ammonia emissions were high for all vehicles and fuels; higher than gasoline and diesel vehicles. The results also showed that, following the introduction of the real-driving emissions regulation, even though not applicable to the examined vehicles, Euro 6d-Temp vehicles had lower emissions compared to the Euro 6b vehicles.

Assessment of On-Board and Laboratory Gas Measurement Systems for Future Heavy-Duty Emissions Regulations

Road transport contributes significantly to air pollution in cities. Regulations across the globe continuously reduce the limits that vehicles need to respect during their lifetimes. Furthermore, more pollutants are being subject to control with new regulations and, most important, testing tends to be done under real-world conditions on the road. In this study, various portable systems were compared with laboratory-grade equipment with a wide range of emissions, focusing on the lower end, where the measurement uncertainty of the instruments is crucial for the determination of emission limits. The engines were diesel- and compressed natural gas (CNG)-fueled. The results were promising, with relatively small differences between portable emissions measurement systems (PEMSs), portable Fourier transform infrared (FTIR) and quantum cascade laser infrared (QCL-IR) spectrometers, and the respective laboratory-grade analyzers based on chemiluminescence detection (CLD), non-dispersive infrared (NDIR), and FTIR principles. The results also highlighted the need for strict technical regulations regarding accuracy and drift for low emission limits in future.

Modelling the Impact of the Introduction of the EURO 6d-TEMP/6d Regulation for Light-Duty Vehicles on EU Air Quality

In this manuscript, we evaluated different emission scenarios for light-duty road transport to evaluate their impact on air quality in the EU, with a focus on a number of cities by means of the EMEP (European Monitoring and Evaluation Programme) modelling system. In addition to the reference case scenario, where exhaust emission factors from COPERT (Computer Programme to calculate Emissions from Road Transport) corresponding to the existing fleet were used, we also tested future potential scenarios considering: (a) all passenger cars and light commercial vehicles meet the EURO 6 emissions standard and EDGAR (Emission Database for Global Atmospheric research) EURO 6 emission factors; (b) all passenger cars and light commercial vehicles meet the EURO 6 emissions standard and real-world emission factors derived from actual Euro 6d-TEMP/6d vehicles. Results show how the replacement of old vehicles by newer ones with better emission control technologies can help improve air quality in the EU in terms of reductions in NO2 and PM2.5 concentrations. However, reduced NOx emissions in cities (as foreseen in the two scenarios analysed) will cause tropospheric O3 to increase.

Measuring Emissions from a Demonstrator Heavy-Duty Diesel Vehicle under Real-World Conditions—Moving Forward to Euro VII

The European Union (EU) has introduced since the early 1990s a series of progressively more stringent emission regulations to control air pollution from the transport sector, commonly known as Euro standards. Following this path, more recently, with the European Green Deal, the European Commission has indicated the intention to review the current air pollutant emissions standards. This study investigates the emission performance of an advanced demonstrator vehicle developed to meet the increasingly more stringent air pollution limits required. Emissions of currently regulated and unregulated components including NH3, N2O, and SPN10 (solid particle number), were studied in a very wide range of real-world operative conditions. The performance of two new generation portable instruments for the onboard measurement of N2O and NH3 were also evaluated in comparison with reference laboratory equipment. Similarly, the measurement accuracy of onboard NOx sensors was also compared to laboratory reference. The vehicle presented low emissions of NOx and NH3 and relatively low emissions of N2O, also compared to data currently available in the literature, in a broad range of operative conditions, which however resulted in a large variability in emissions.

A Computer Tool Using OpenModelica for Modelling CO2 Emissions in Driving Tests

The transport sector is one of the main barriers to achieving the European Union’s climate protection objectives. Therefore, more and more restrictive legal regulations are being introduced, setting out permissible limits for the emission of toxic substances emitted into the atmosphere, promoted biofuels and electromobility. The manuscript presents a computer tool to model the total energy consumption and carbon dioxide emissions of vehicles with an internal combustion engine of a 2018 Toyota Camry LE. The calculation tool is designed in the OpenModelica environment. Libraries were used for this purpose to build models of vehicles in motion: VehicleInterfaces, EMOTH (E-Mobility Library of OTH Regensburg). The tool developed on the basis of actual driving test data for the selected vehicle provides quantitative models for the instantaneous value of the fuel stream, the model of the instantaneous value of the carbon dioxide emission stream as a function of speed and the torque generated by the engine. In the manuscript, the tests were conducted for selected driving cycles tests: UDDS (EPA Urban Dynamometer Driving Schedule), HWFET (Highway Fuel Economy Driving Schedule), EPA US06 (Environmental Protection Agency; Supplemental Federal Test Procedure (SFTP)), LA-92 (Los Angeles 1992 driving schedule), NEDC (New European Driving Cycle), and WLTP (Worldwide Harmonized Light-Duty Vehicle Test Procedure). Using the developed computer tool, the impact on CO2 emissions was analyzed in the context of driving tests with four types of fuels: petrol 95, ethanol, methanol, DME (dimethyl ether), CNG (compressed natural gas), and LPG (liquefied petroleum gas).

Environmental and human health impact of different powertrain passenger cars in a life cycle perspective. A focus on health risk and oxidative potential of particulate matter components

Different powertrains passenger cars, homologate in compliance with Euro 6 standard, were compared in a life cycle perspective for assessing both environmental and human health impacts. For this latter aspect, some correlation between the emission of heavy metals, elemental carbon, organic carbon, the oxidative potential of particulate matter and the adverse effect on human health were also analyzed and discussed. Battery electric vehicle (BEV) showed the lower greenhouse gases emissions, from 0.1 kgCO_2eq/km to 0.2 kgCO_2eq/km but were charged by the higher emissions of freshwater eutrophication and freshwater ecotoxicity, about 6 × 10^-6 kgP_eq/km and 4 CTUe/km, respectively. Lower resource depletion was detected for cars powered by internal combustion and hybrid powertrains. Amount of particulate matter (PM) emitted resulted lower for petrol-hybrid electric vehicles (Petrol-HEV), of about 5 × 10^-5 kgPM_2.5eq/km. BEV were charged by the higher values of human toxicity cancer, from about 2 × 10^-5 CTU_h/km to about 5 × 10^-5 CTU_h/km whereas Petrol-HEV were credited by the lower impact on human health (DALY/km). The large contribution to PM emission from all the analyzed cars was from tyre and brake wear. Main PM components were elemental (ElC) and organic carbon (OC) compounds. ElC is also a specific marker of PM emitted from traffic. Both ElC and OC were characterized by a strong correlation with the oxidative potential of PM, indicating a threat for human respiratory tract only marginally decreased by the transition from conventional to electric poweretrains vehicles.

NH3 and N2O Real World Emissions Measurement from a CNG Heavy Duty Vehicle Using On-Board Measurement Systems

The development and utilization of a series of after-treatment devices in modern vehicles has led to an increase in emissions of NH3 and/or N2O with respect to the past. N2O is a long-lived greenhouse gas and an ozone-depleting substance, while NH3 is a precursor of secondary aerosols in the atmosphere. Certain regions, e.g., the EU and the USA, have introduced limits to the emissions of NH3 or N2O for vehicles tested in the laboratory. However, due to the lack of on-board systems that allow for the measurement of these compounds when the regulations were developed, these vehicles’ real-world emissions have not been regulated. This work evaluates on-board systems that could allow measuring real-world emissions of NH3 and N2O from heavy-duty vehicles. In particular, emissions of NH3 or N2O from a Euro VI Step D urban/interurban bus fueled with Compressed Natural Gas were measured using the HORIBA’s OBS-ONE-XL, which is based on a specifically developed technique called Infrared Laser Absorption Modulation, and uses a Quantum Cascade Laser as a light source. They were also measured using the PEMS-LAB, which is a more conventional FTIR-based system. Emissions were measured under real-world driving conditions on the road and in a climatic test cell at different ambient temperatures. For most of the conditions tested, the on-board systems correlated well with a laboratory-grade FTIR used as reference. In addition, a good correlation with R2 > 0.9 was found for the N2O concentrations measured by OBS-ONE-XL and PEMS-LAB during on-road testing.

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO)

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH3-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH3) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH3 emissions is proposed, NH3 emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH3 oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH3 conversion, high selectivity to N2O and NOx as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.

Fourier Transform Infrared (FTIR) Spectroscopy for Measurements of Vehicle Exhaust Emissions: A Review

Pollution from vehicles is a serious concern for the environment and human health. Vehicle emission regulations worldwide have limits for pollutants such as hydrocarbons, CO, and NOx. The measurements are typically conducted at engine dynamometers (heavy-duty engines) sampling from the tailpipe or at chassis dynamometers (light-duty vehicles) sampling from the dilution tunnel. The latest regulations focused on the actual emissions of the vehicles on the road. Greenhouse gases (GHG) (such as CO2, CH4, N2O), and NH3 have also been the subject of some regulations. One instrument that can measure many gaseous compounds simultaneously is the Fourier transform infrared (FTIR) spectrometer. In this review the studies that assessed FTIRs since the 1980s are summarized. Studies with calibration gases or vehicle exhaust gas in comparison with well-established techniques were included. The main conclusion is that FTIRs, even when used at the tailpipe and not at the dilution tunnel, provide comparable results with other well-established techniques for CO2, CO, NOx, while for hydrocarbons, higher deviations were noticed. The introduction of FTIRs in the regulation needs a careful description of the technical requirements, especially interference tests. Although the limited results of prototype portable FTIRs for on-road measurement are promising, their performance at the wide range of environmental conditions (temperature, pressure, vibrations) needs further studies.

Effect of Extreme Temperatures and Driving Conditions on Gaseous Pollutants of a Euro 6d-Temp Gasoline Vehicle

Gaseous emissions of modern Euro 6d vehicles, when tested within real driving emissions (RDE) boundaries, are, in most cases, at low levels. There are concerns, though, about their emission performance when tested at or above the boundaries of ambient and driving conditions requirements of RDE regulations. In this study, a Euro 6d-Temp gasoline direct injection (GDI) vehicle with three-way catalyst and gasoline particulate filter was tested on the road and in a laboratory at temperatures ranging between −30 °C and 50 °C, with cycles simulating urban congested traffic, uphill driving while towing a trailer at 85% of the vehicle’s maximum payload, and dynamic driving. The vehicle respected the Euro 6 emission limits, even though they were not applicable to the specific cycles, which were outside of the RDE environmental and trip boundary conditions. Most of the emissions were produced during cold starts and at low ambient temperatures. Heavy traffic, dynamic driving, and high payload were found to increase emissions depending on the pollutant. Even though this car was one of the lowest emitting cars found in the literature, the proposed future Euro 7 limits will require a further decrease in cold start emissions in order to ensure low emission levels under most ambient and driving conditions, particularly in urban environments. Nevertheless, motorway emissions will also have to be controlled well.

Structural Evolution of Bimetallic PtPd/CeO2 Methane Oxidation Catalysts Prepared by Dry Milling

Bimetallic Pt-Pd catalysts supported on ceria have been prepared by mechanochemical synthesis and tested for lean methane oxidation in dry and wet atmosphere. Results show that the addition of platinum has a negative effect on transient light-off activity, but for Pd/Pt molar ratios between 1:1 and 8:1 an improvement during time-on-stream experiments in wet conditions is observed. The bimetallic samples undergo a complex restructuring during operation, starting from the alloying of Pt and Pd and resulting in the formation of unprecedented "mushroom-like" structures consisting of PdO bases with Pt heads as revealed by high-resolution transmission electron microscopy (HRTEM) analysis. On milled samples, these structures are well-defined and observed at the interface between palladium and ceria, whereas those on the impregnated catalyst appear less ordered and are located randomly on the surface of ceria and of large PdPt clusters. The milled catalyst prepared by first milling Pd metal and ceria followed by the addition of Pt shows better performances compared to a conventional impregnated sample and also to a sample obtained by inverting the Pd-Pt milling order. This has been ascribed to the intimate contact between Pd and CeO₂ generated at the nanoscale during the milling process.

Emission factors of ammonia for on-road vehicles in urban areas from a tunnel study in south China with laser-absorption based measurements

Vehicle emission is an important source of ammonia (NH₃) in urban areas. To better address the role of vehicle emission in urban NH₃ sources, the emission factor of NH₃ (NH₃-EF) from vehicles running on roads under real-world conditions (on-road vehicles) needs to update accordingly with the increasingly tightened vehicle emission standards. In this study, laser-absorption based measurements of NH₃ were conducted during a six-day campaign in 2019 at a busy urban tunnel with a daily traffic flow of nearly 40,000 vehicles in south China's Pearl River Delta (PRD) region. The NH₃-EF was measured to be 16.6 ± 6.3 mg km^-1 for the on-road vehicle fleets and 19.0 ± 7.2 mg km^-1 for non-electric vehicles, with an NH₃ to CO₂ ratio of 0.27 ± 0.09 ppbv ppmv^-1. Multiple linear regression revealed that the average NH₃-EFs for gasoline vehicles (GVs), liquefied petroleum gas vehicles, and heavy-duty diesel vehicles (HDVs) were 18.8, 15.6, and 44.2 mg km^-1, respectively. While NH₃ emissions from GVs were greatly reduced with enhanced performance of engines and catalytic devices to meet stricter emission standards, the application of urea selective catalytic reduction (SCR) in HDVs makes their NH₃ emission an emerging concern. Based on results from this study, HDVs may contribute over 11% of the vehicular NH₃ emissions, although they only share ∼4% by vehicle numbers in China. With the updated NH₃-EFs, NH₃ emission from on-road vehicles was estimated to be 9 Gg yr^-1 in the PRD region in 2019, contributing only 5% of total NH₃ emissions in the region, but still might be a dominant NH₃ source in the urban centers with little agricultural activity.

Real Driving Emission Calibration—Review of Current Validation Methods against the Background of Future Emission Legislation

Reducing air pollution caused by emissions from road traffic, especially in urban areas, is an important goal of legislators and the automotive industry. The introduction of so-called “Real Driving Emission” (RDE) tests for the homologation of vehicles with internal combustion engines according to the EU6d legislation was a fundamental milestone for vehicle and powertrain development. Due to the introduction of non-reproducible on-road emission tests with “Portable Emission Measurement Systems” (PEMS) in addition to the standardized emission tests on chassis dynamometers, emission aftertreatment development and validation has become significantly more complex. For explicit proof of compliance with the emission and fuel consumption regulations, the legislators continue to require the “Worldwide Harmonized Light Duty Vehicle Test Cycle” (WLTC) on a chassis dynamometer. For calibration purposes, also various RDE profiles are conducted on the chassis dynamometer. However, the combination of precisely defined driving profiles on the chassis dynamometer and the dynamics-limiting boundary conditions in PEMS tests on the road still lead to discrepancies between the certified test results and the real vehicle behavior. The expected future emissions standards to replace EU6d will therefore force even more realistic RDE tests. This is to be achieved by significantly extending the permissible RDE test boundary conditions, such as giving more weight to the urban section of an RDE test. In addition, the introduction of limit values for previously unregulated pollutants such as nitrogen dioxide (NO2), nitrous oxide (N2O), ammonia (NH3) and formaldehyde (CH2O) is being considered. Furthermore, the particle number (for diameters of solid particles > 10 nm: PN10), the methane (CH4) emissions and emissions of non-methane organic gases (NMOG) shall be limited and must be tested. To simplify the test procedure in the long term, the abandonment of predefined chassis dyno emission tests to determine the pollutant emission behavior is under discussion. Against this background, current testing, validation, and development methods are reviewed in this paper. New challenges and necessary adaptations of current approaches are discussed and presented to illustrate the need to consider future regulatory requirements in today’s approaches. Conclusions are drawn and suggestions for a robust RDE validation procedure are formulated.

Role of Vehicular Catalytic Converter Temperature in Emission of Pollutants: An Assessment Based on Isotopic Analysis of CO2 and N2O

Vehicular catalytic converters are used to regulate, reduce, and convert toxic and environmentally unfriendly compounds in exhaust gases into relatively inert and less harmful chemical species. The efficiency, however, is largely affected by the operating temperature of the converter which is set by the hot exhaust gas released from the combustion chamber. A major gas released during combustion is CO₂, and its multiply substituted isotopocule, namely, ¹³C¹⁶O¹⁸O, provides a window of opportunity to probe directly the effective temperature of the converter in operation. Here, we report multiple isotopic measurements in exhaust CO₂ (δ¹³C, δ¹⁷O, δ¹⁸O, and Δ₄₇) of diesel (trucks and buses) and gasoline (sedans, trucks, and two-wheel motorcycles)-powered vehicles. For investigating the efficiency of a converter in reducing toxic compounds, we studied NO_x processes through isotopic analysis of the exhaust N₂O. We found that the degree of N₂O reduction to N₂ in gasoline-powered vehicles is high when the temperature is above 200 °C (inferred by Δ₄₇). In contrast, diesel-powered vehicles produce N₂O in abundance, probably a consequence of selective catalytic reduction of NO_x, and the reduction efficiency depends on the converter temperature. In other words, the catalytic converters act as sinks and sources of N₂O to the atmosphere in gasoline- and diesel-operated vehicles, respectively. We also report a new set of field data by measuring the isotopic compositions of CO₂ and N₂O in the Hsuehshan tunnel, a ∼13 km long highway tunnel in Taiwan. Elevated N₂O concentrations inside the tunnel indicate that the emission of N₂O by heavy-duty diesel vehicles is much higher compared to the reduction by gasoline-operated passenger cars, making the vehicular exhausts a net source of N₂O to the atmosphere. The combined study of clumped isotopes and N₂O concentration in exhaust gases suggests that it is useful to probe the operational temperature of catalytic converters and monitor the pollution level in operation, thus providing an opportunity for manufacturers to optimize the catalytic efficiency to reduce the level of toxic pollutants to the environment.

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH3 and N2O. The NOx, N2O, and NH3 emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH3 and N2O is observed in both Diesel and gasoline light-duty vehicles, whereby NH3 emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH3 emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N2O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles.

Assessment of Petrol and Natural Gas Vehicle Carbon Oxides Emissions in the Laboratory and On-Road Tests

The problem of global warming and the related climate change requires solutions to reduce greenhouse gas emissions, in particular CO2. As a result, newly manufactured cars consume less fuel and emit lower amounts of CO2. In terms of exhaust emissions and fuel consumption, old cars are significantly inferior to the more recent models. In Poland, for instance, the average age of passenger cars is approximately 13 years. Therefore, apart from developing new solutions in the cars produced today, it is important to focus on measures that enable the reduction in CO2 emissions in older vehicles. These methods include the adaptation of used cars to run on gaseous fuels. Natural gas is a hydrocarbon fuel that is particularly preferred in terms of CO2 emissions. The article presents the results of research of carbon oxides emission (CO, CO2) in the exhaust gas of a passenger car fueled by petrol and natural gas. The emissions were measured under the conditions of the New European Driving Cycle (NEDC) test and in real road tests. The test results confirm that compared to petrol, a CNG vehicle allows for a significant reduction in CO2 and CO emissions in a car that is several years old, especially in urban traffic conditions.

A Computer Tool for Modelling CO2 Emissions in Driving Cycles for Spark Ignition Engines Powered by Biofuels

A driving cycle is a record intended to reflect the regular use of a given type of vehicle, presented as a speed profile recorded over a certain period of time. It is used for the assessment of engine pollutant emissions, fuel consumption analysis and environmental certification procedures. Different driving cycles are used, depending on the region of the world. In addition, drive cycles are used by car manufacturers to optimize vehicle drivelines. The basis of the work presented in the manuscript was a developed computer tool using tests on the Toyota Camry LE 2018 chassis dynamometer, the results of the optimization process of neural network structures and the properties of fuels and biofuels. As a result of the work of the computer tool, the consumption of petrol 95, ethanol, methanol, DME, CNG, LPG and CO2 emissions for the vehicle in question were analyzed in the following driving tests: Environmental Protection Agency (EPA US06 and EPA USSC03); Supplemental Federal Test Procedure (SFTP); Highway Fuel Economy Driving Schedule (HWFET); Federal Test Procedure (FTP-75–EPA); New European Driving Cycle (NEDC); Random Cycle Low (×05); Random Cycle High (×95); Mobile Air Conditioning Test Procedure (MAC TP); Common Artemis Driving Cycles (CADC–Artemis); Worldwide Harmonized Light-Duty Vehicle Test Procedure (WLTP).

Non-Volatile Particle Number Emission Measurements with Catalytic Strippers: A Review

Vehicle regulations include limits for non-volatile particle number emissions with sizes larger than 23 nm. The measurements are conducted with systems that remove the volatile particles by means of dilution and heating. Recently, the option of measuring from 10 nm was included in the Global Technical Regulation (GTR 15) as an additional option to the current >23 nm methodology. In order to avoid artefacts, i.e., measuring volatile particles that have nucleated downstream of the evaporation tube, a heated oxidation catalyst (i.e., catalytic stripper) is required. This review summarizes the studies with laboratory aerosols that assessed the volatile removal efficiency of evaporation tube and catalytic stripper-based systems using hydrocarbons, sulfuric acid, mixture of them, and ammonium sulfate. Special emphasis was given to distinguish between artefacts that happened in the 10–23 nm range or below. Furthermore, studies with vehicles’ aerosols that reported artefacts were collected to estimate critical concentration levels of volatiles. Maximum expected levels of volatiles for mopeds, motorcycles, light-duty and heavy-duty vehicles were also summarized. Both laboratory and vehicle studies confirmed the superiority of catalytic strippers in avoiding artefacts. Open issues that need attention are the sulfur storage capacity and the standardization of technical requirements for catalytic strippers.

Assessment of Gaseous and Particulate Emissions of a Euro 6d-Temp Diesel Vehicle Driven >1300 km Including Six Diesel Particulate Filter Regenerations

Diesel-fueled vehicles have classically had high particulate and NOx emissions. The introduction of Diesel Particulate Filters (DPFs) and Selective Catalytic Reduction for NOx (SCR) systems have decreased the Particle Number (PN) and NOx emissions, respectively, to very low levels. However, there are concerns regarding the emissions released during the periodic DPF regenerations, which are necessary to clean the filters. The absolute emission levels and the frequency of the regenerations determine the contribution of regenerations, but where they happen (city or highway) is also important due to different contributions to human exposure. In this study, we measured regulated and non-regulated emissions of a Euro 6d-temp vehicle both in the laboratory and on the road. PN and NOx emissions were similar in the laboratory and on-the road, ranging around 1010 p/km and 50 mg/km, respectively. Six regeneration events took place during the 1300 km driven, with an average distance between regeneration events of only 200 km. During regeneration events, the laboratory limits for PN and NOx, although not applicable, were exceeded in one of the two measured events. However, the on-road emissions were below the applicable not-to-exceed limits when regenerations occurred. The weighted PN and NOx emissions over the regeneration distance were approximately two times below the applicable limits. The N2O emissions were <14 mg/km and NH3 at instrument background level (<1 ppm), reaching 8 ppm only during regeneration. The results of this study indicate that due to the short interval between regenerations, studies of diesel vehicles should report the emissions during regeneration events.