Portable Emission Measurement System Research Articles

Investigation of real-world emissions of China III and China IV buses in a high-altitude city: A case study of Lhasa

Limitations still remain among vehicle emissions standards and regulations about high-altitude areas at altitude over 2400 m. In view of high vehicle-use intensity for buses, on-road measurements were performed on four heavy-duty diesel vehicles by employing a portable emissions measurement system (PEMS) in Lhasa, with an average elevation of approximately 3650 m. The result indicated that under real-world driving conditions of Lhasa, compared with China III buses, China IV buses did not show excellent emission performance consistently. For example, carbon monoxide (CO) emission factor of China III-5.2L buses is 2.4 times of China IV-5.2L buses, while the nitrogen oxides (NOx) is only 36% of China IV-5.2L. Furthermore, an operating mode binning and a micro-trips method are used to link real-world emissions of each vehicle to driving conditions. For China III-5.2L and China IV-5.2L buses, we found strong correlations between relative emission factors of carbon dioxide (CO2) and NOx and average speed. However, these correlations for China IV-7.8L bus were less strong. This phenomenon proves that the role of traffic conditions in affecting road driving emissions would be mitigated when selective catalytic reduction (SCR) functioning properly. This study have potential implications for policymakers concerning vehicle emissions management and control strategies, such as promotion of alternative fuel with in-used buses, aimed at emissions reduction.

Liquified Petroleum Gas-Fuelled Vehicle CO2 Emission Modelling Based on Portable Emission Measurement System, On-Board Diagnostics Data, and Gradient-Boosting Machine Learning

One method to reduce CO2 emissions from vehicle exhaust is the use of liquified petroleum gas (LPG) fuel. The global use of this fuel is high in European countries such as Poland, Romania, and Italy. There are a small number of computational models for the purpose of estimating the emissions of LPG vehicles. This work is one of the first to present a methodology for developing microscale CO2 emission models for LPG vehicles. The developed model is based on data from road tests using the portable emission measurement system (PEMS) and on-board diagnostic (OBDII) interface. This model was created from a previous exploratory data analysis while using gradient-boosting machine learning methods. Vehicle velocity and engine RPM were chosen as the explanatory variables for CO2 prediction. The validation of the model indicates its good precision, while its use is possible for the analysis of continuous CO2 emissions and the creation of emission maps for environmental analyses in urban areas. The validation coefficients for the selected gradient-boosting method of modelling CO2 emissions for an LPG vehicle are the R2 test of 0.61 and the MSE test of 0.77.

Carbon-emission calculation method during operation period based on asphalt pavement performance

Current vehicle carbon emission models tend to ignore the influence of road roughness on driving speed selection, which may damage the carbon emission evaluation accuracy. In this study, first, based on the results obtained with a portable emissions measurement system (PEMS), an explicit model for user vehicle carbon emissions, driving speed, and pavement roughness is established. Second, the influence of road roughness on driver behavior choice is investigated, and an interrelationship model between roughness and driving speed choice is developed. Finally, a more realistic carbon emission calculation model during the operation period is proposed based on the pavement performance model, and the accuracy is verified in comparison with the traditional vehicle operating cost (VOC) model. It is found that there exists a carbon emission minimization point under free-flow conditions, and the corresponding driving speed is the optimal speed point of user vehicles, i.e. 63 km/h. In addition, a great linear correlation exists between the roughness and driving speed selection, which should be considered in the final calculation model. The vehicle carbon emission model developed in this research provides solid references for evaluating the life-cycle emission of asphalt pavement and guiding the selection of maintenance strategies for the pavement to lower carbon emissions.

Investigation of Heavy-Duty Vehicle Chassis Dynamometer Fuel Consumption and CO2 Emissions Based on a Binning-Reconstruction Model Using Real-Road Data

Global warming is directly related to heavy-duty vehicle fuel consumption and greenhouse gas (CO2 mainly) emissions, which, in China, are certified on the vehicle chassis dynamometer. Currently, vast amounts of vehicle real-road data from the portable emission measurement system (PEMS) and remote monitoring are being collected worldwide. In this study, a binning-reconstruction calculation model is proposed, to predict the chassis dynamometer fuel consumption and CO2 emissions with real-road data, regardless of operating conditions. The model is validated against chassis dynamometer and PEMS test results, and remote monitoring data. Furthermore, based on the proposed model, the fuel consumption levels of 1408 heavy-duty vehicles in China are analyzed, to evaluate the challenge to meet the upcoming China fourth stage fuel consumption limits. For accumulated fuel consumption based on the on-board diagnostic (OBD) data stream, a predictive relative error less than 5% is expected for the present model. For bag sampling results, the proposed model’s accuracy is expected to be within 10%. The average relative errors between the average fuel consumption and the China fourth stage limits are about 3%, 8%, and 0.7%, for current trucks, tractors, and dump trucks, respectively. The urban operating condition, with lower vehicle speeds, is the main challenge for fuel consumption optimization.

Measurement of Gaseous Exhaust Emissions of Light-Duty Vehicles in Preparation for Euro 7: A Comparison of Portable and Laboratory Instrumentation

The European Union’s ambition to reach climate neutrality and a toxic-free environment by 2050 entails, among other things, cleaner road vehicles. The European Commission’s proposal for the next regulatory emissions standard, Euro 7, requires the measurement of pollutants currently not regulated on the road. In this study we compared a prototype portable emissions measurement system (PEMS) measuring CO2, CO, NO, NO2, N2O, NH3, CH4, and HCHO based on infrared laser absorption modulation (IRLAM), and two Fourier transform infrared (FTIR) spectrometers with laboratory grade analyzers. To this end, one Euro 6d Diesel, one Euro 6d gasoline, and one Euro 4 gasoline vehicle were tested at −7 °C and 23 °C with various driving cycles covering traffic conditions to highway dynamic driving. The results demonstrated that the differences among the instruments were small: ±1 mg/km for HCHO, N2O, and CH4, ±2.5 mg/km for NH3, ±10–15 mg/km for NOx, ±50 mg/km or ±15% for CO (whichever was larger), and ±10–15 g/km for CO2. These values corresponded to <10–15% of the proposed Euro 7 limits or the emission levels of the tested vehicles. Our results confirm the feasibility of on-board systems to measure the conventional components including CO2 and the aforementioned additional pollutants.

REAL-TIME EMISSIONS OF GASEOUS POLLUTANTS FROM VEHICLES UNDER HETEROGENEOUS TRAFFIC CONDITIONS

Air quality problems in cities are often a cause for worry. The air quality index is increasing daily, leading to an increase in cancer and many respiratory problems. Road transport in an urban area is a significant cause of air pollution. The vehicles must meet Indian emission regulations for which the emissions are measured using legally mandated standard driving cycles that did not accurately reflect real-world driving emissions because of varying traffic conditions, meteorological conditions, driving behaviour, vehicle power, performance, etc. This study focuses on real-time emissions of gaseous pollutants hydrocarbon (HC), carbon dioxide (CO2), carbon monoxide (CO), and nitric oxide (NO) from vehicle exhaust pipes under heterogeneous traffic conditions. The emissions were measured using a Portable Emission Measurement System (PEMS). The PEMS used was an AVL MDS 450 analyser mounted on the vehicle, and on-road emissions were captured. The test sample consists of four passenger vehicles with varying engine sizes, manufacturers, and fuel. The test route comprises city and highway areas, and it was discovered that the emissions were reduced by 40 to 70% on highways compared to the city. In petrol BSIV and BSVI engines, the emission was reduced to 41.73% for CO, 46.90% for HC, and 64% for NO in the city area. Speed and emissions scatter graphs were plotted for the vehicles, and it was found that in the city area, the optimum speed for less emission is between 30-40 km/h, and on highways, the optimum speed is 80-90 km/h. The emissions were also sensitive to the rate and frequency of acceleration and decelerations. This type of study is very limited in India, and more such studies are required for the assessment of air quality in metropolitan areas and successful traffic management strategies, as well as for determining instantaneous projections of pollutant emissions.

Impacts on real-world extra cold start emissions: Fuel injection, powertrain, aftertreatment and ambient temperature

Vehicles emit substantial amounts of pollutants during start periods. Engine starts mainly occur in urban areas, causing serious harm to humans. To investigate the impacts on extra cold start emissions (ECSEs), eleven China 6 vehicles with various control technologies (fuel injection, powertrain, and aftertreatment) were monitored with a portable emission measurement system (PEMS) at different temperatures. For conventional internal combustion engine vehicles (ICEVs), the average ECSEs of CO2 increased by 24%, while the average ECSEs of NOx and particle number (PN) decreased by 38% and 39%, respectively, with air conditioning (AC) on. Gasoline direct injection (GDI) vehicles had 5% lower CO2 ECSEs, but 261% higher NOx ECSEs and 318% higher PN ECSEs than port fuel injection (PFI) vehicles at 23 °C. The average PN ECSEs were significantly reduced by gasoline particle filters (GPFs). The GPF filtration efficiency was higher in GDI than PFI vehicles due to particle size distribution. Hybrid electric vehicles (HEVs) generated excessive PN extra start emissions (ESEs), resulting in a 518% increase compared to ICEVs. The start times of the GDI-engine HEV accounted for 11% of the whole test time, but the proportion of PN ESEs relative to total emissions were 23%. Linear simulation based on the decrease in ECSEs with increasing temperature underestimated the PN ECSEs from PFI and GDI vehicles by 39% and 21%, respectively. For ICEVs, CO ECSEs varied with temperature in a U shape with a minimum at 27 °C; NOx ECSEs decreased as ambient temperature increased; PFI vehicles generated more PN ECSEs at 32 °C than GDI vehicles, stressing the significance of ECSEs at high temperature. These results are useful for improving emission models and assessing air pollution exposure in urban aeras.

Real-world emission for in-use non-road construction machinery in Wuhan, China.

Non-road construction machinery (NRCM) emissions pollutants significantly impact air quality. Six typical NRCM (2 excavators, 3 loaders, and 1 forklift) are analyzed based on a portable emission measurement system (PEMS) in Wuhan to estimate the real-world emission characteristics and chemical composition of PM2.5 of NRCM. The results show that the fuel-based average emission factors (EFs) of carbon monoxide (CO), hydrocarbon (HC), nitrogen oxides (NOx), and particulate matter (PM) are 19.4 ~ 35.7gkg-1 fuel, 2.9 ~ 7.9gkg-1 fuel, 57.5 ~ 95.3gkg-1 fuel, and 1.8 ~ 2.6gkg-1 fuel for the tested NRCM. The high NOx EF implies that the regulation of NOx emission in Wuhan should be strengthened. In addition, the PM2.5 chemical composition profiles for NRCM show that the PM2.5 emitted from NRCM is dominated by organic carbon and elemental carbon (56.11 ~ 73.85%), followed by water-soluble ions (WSIs, 1.47 ~ 3.46%), and elements (0.16 ~ 0.41%). The major WSIs species are Cl-, Na+ andNO3-, and the major elements are Ca, Na, and K, which are important markers for PM2.5 source analysis. The results of EFs and chemical composition emission characteristics of NRCM tailpipe pollutants obtained in the real-world can provide essential data support for accurately establish of emission inventory of non-road mobile sources in Wuhan.

Comparative Analysis of Emission Characteristics of In-Use China II–V Gasoline, Hybrid, Diesel-Fueled Vehicles

Increasingly stringent regulations regarding vehicle emissions have contributed to the diversification of vehicle technologies, resulting in the increasing complexity of typical vehicles that make up a fleet. In order to investigate the real gas emissions of different typical vehicles, tests were conducted using a portable emission measurement system (PEMS) in Beijing and emission studies were conducted on eight light-duty passenger vehicles (LDPVs, including light-duty gasoline passenger vehicles and hybrid electric vehicles), eight heavy-duty passenger vehicles (HDPVs), and four light-duty trucks (LDTs). The results show that the emissions of relevant pollutants from LDPV meet the emission standard limits. The emission factors of CO2, CO, NOX, and HC of China IV and China V hybrid electric vehicles (HEVs) are much smaller than the emission standard limits and the emission factors of other vehicles, which have better emission reduction effects. Among LDPV, heavy-duty passenger vehicles (HDPVs), and LDT, the emissions of HDPV and LDT are extremely high. Emission characteristics vary on different types of roads, with the highest emission factors generally occurring on secondary roads. The micro-trip method was used to explore the influence of speed on emission factors. HEV are less sensitive to speed changes and can still maintain a low emission level at low speeds. The average speed and emission factors of HDPV in micro-trip has a strong correlation.

Real-world emissions and ozone formation potential of carbonyl compounds originating from construction machinery based on a portable emission measurement system

Real-world emissions and ozone formation potential of carbonyl compounds originating from construction machinery based on a portable emission measurement system

Characterizing Operating Condition-Based Formaldehyde Emissions of Light-Duty Diesel Trucks in China Using a PEMS-HCHO System.

Formaldehyde (HCHO) plays a critical role in atmospheric photochemistry and public health. While existing studies have suggested that vehicular exhaust is an important source of HCHO, the operating condition-based diesel truck HCHO emission measurements remain severely limited due to the limited temporal resolution and accuracy of measurement techniques. In this study, we characterized the second-by-second HCHO emissions from 29 light-duty diesel trucks (LDDTs) in China over dynamometer and real-world driving tests using a portable online HCHO emission measurement system (PEMS-HCHO), considering various operating conditions. Our results suggested that the HCHO emissions from LDDTs might be underestimated by the widely used offline DNPH-HPLC method. The HCHO emissions at a 200 s cold start from China V LDDT can be up to 50 mg/start. Different driving conditions over dynamometer and real-world driving tests led to a 2-4 times difference in the HCHO emission factors (EFs). Under real-world hot-running conditions, the HCHO EFs of China III, IV, V, and VI LDDTs were 43.5 ± 35.7, 10.6 ± 14.2, 8.8 ± 5.1, and 3.2 ± 1.2 mg/km, respectively, which significantly exceeded the latest California low emission vehicle III HCHO emission standard (2.5 mg/km). These findings highlighted the significant impact of vehicle operating conditions on HCHO emissions and the urgency of regulating HCHO emissions from LDDTs in China.

Design and evaluation of a volatile particle remover combining hot dilution and a thermodenuder

Portable and efficient removal of volatile particles from motor vehicle exhaust is essential for the accurate measurement of involatile solid particle number concentration in on-board emission measurement systems. For this purpose, a volatile particle remover with a combination of hot dilution and a thermodenuder (referred to as VPR-TD) was designed. The flow and temperature fields of the VPR-TD were simulated and analyzed by COMSOL Multiphysics software by which experimental verification and system performance tests were performed. The simulation showed that the effective heating length and residence time of the VPR-TD increased by 6 cm and 25%, respectively, as the dilution ratio increased from 1 to 10 at a total flow of 0.6 L/min at 350 °C. In addition, the experimental results showed that the penetration efficiency of 100 nm sodium chloride (non-volatile particles) in the VPR-TD was higher than 70.4%, and the removal efficiency of 30 nm tetracontane (volatile particles) was higher than 99% at a total flow 0.6 L/min, heating temperature 350 °C, and dilution ratios of 5 and 10. In summary, when the dilution ratio was set to 10, the device met the requirements of the Light Duty Vehicle Emission Limits and Measurement Methods (CHINA 6) for a volatile particle remover. At dilution ratio of 5, VPR-TD may be used as a pre-conditioning unit in portable emissions measurement systems.

USE OF TEST CYCLES FOR STUDYING THE OPERATIONAL PROPERTIES OF TRANSPORT CONSTRUCTION MACHINERY

The article discusses the main test cycles that can be used to evaluate the operational properties of transport construction machines. In particular, with their help, it is possible to study the environmental safety and fuel efficiency of machines of various purposes, which are used in transport construction. The work presents the methods and procedures by which the operational properties of such machines are investigated. The considered test cycles of engines of agricultural machinery, road construction machines, excavators, ship, industrial and locomotive engines, provided by the international standard ISO 8178. This standard consists of 11 chapters, which describe in detail the test procedure and methods of measuring the content of harmful substances in exhaust gases of various types engines, fuel type requirements and analysis of the obtained results. ISO 8178 contains a series of engine bench test cycles designed for different classes of engines and equipment, each of which is a sequence of steady-state or transient modes with different load factors. In the event that conducting tests on a motor stand is difficult, this standard provides for measurement under operating conditions. In this case, the standard test cycles do not apply and the tests are carried out while the vehicle is operating in its normal operating mode. Emissions are measured using the Portable emissions measurement system (PEMS). Test cycles are one of the effective tools for evaluating the fuel economy and environmental performance of transport construction machines. They allow you to get a lot of useful information about various aspects of the machines, such as fuel consumption, emissions of harmful substances, noise level, engine efficiency, etc. One of the disadvantages of using test cycles is their limited versatility. Different types of machines have their own unique features, so in order to achieve the maximum efficiency of research, it is necessary to develop test cycles that correspond to the specifics of different types of machines.

Quantifying start emissions and impact of reducing cold and warm starts for gasoline and hybrid vehicles

In this study, a portable emissions measurement system (PEMS) was used to measure trip emissions of a gasoline vehicle (2020 Hyundai Tucson Preferred) and a hybrid vehicle (2020 Ford Fusion Hybrid Titanium) under various soak times (12 h–1 min) along two driving routes in Toronto, Canada (highway and city core). A new method was proposed to identify start emissions in a PEMS test, employing confidence intervals (CIs) of hot-running emission rates, and distributions of hot-running coolant and catalyst temperatures. In addition, GPS data reflecting one-week of travel for 82 drivers in Toronto were used to quantify the contributions of start emissions under realistic trip schedules and to estimate the benefits of reducing cold and warm starts. In Toronto, over 95% of the trips have a soak time over 1 h, and over 33% of the trips are within 5 km. Compared to the Tucson, the Fusion Hybrid generates approximately 43.4% less carbon dioxide (CO2) and 77.7% less nitrogen oxides (NOx), but 183.6% more carbon monoxide (CO) and 15.8% more ultrafine particles (measured in particle number, PN), on a representative Toronto drive schedule. For soak times greater than 12 h and trip distance less than 5 km, the contributions of starts to total trip emissions for CO2, CO, NOx, and PN are in the ranges of 13.4%–70.0%, 93.5%–99.9%, 22.3%–73.9%, and 80.3%–99.3%, respectively, for the Tucson. For the Fusion Hybrid, these contributions are in the ranges of 31.4%–95.6%, 25.1%–73.2%, 58.7%–95.9%, and 25.6%–87.7%. With engine and catalyst preheating, total trip emissions for CO2, CO, NOx, and PN decrease on average by 5.1%, 81.3%, 20.2%, and 48.1%, respectively, for the Tucson. For the Fusion Hybrid, these reductions are 10.4%, 16.3%, 40.8%, and 7.9%.

Contribution of Cold Starts to Real-World Trip Emissions for Light-Duty Gasoline Vehicles

For catalytic converter-equipped light-duty gasoline vehicles (LDGV), the hot-stabilized tailpipe emissions for pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) are well controlled. However, there are few reported real-world measurements of cold starts. Idling cold start and hot-stabilized trip exhaust emissions were measured for 37 LDGVs using a portable emissions measurement system (PEMS). Five vehicles were also measured for transient driving cold starts. On average, it took approximately 400, 150, 330, and 120 s to accumulate 90 percent of the idle cold start increments for fuel use, CO, HC, and NOx, respectively. Driving cold start increments were substantially higher than idling cold start increments, whereas cold start duration was typically shorter. For example, driving cold start contributed approximately 64%, 68%, 58%, and 4.5% of the trip total CO, HC, NOx, and carbon dioxide (CO2), respectively. This study is unique in quantifying the cold start contribution on a trip basis with real-world data. Although the cold start increment is sensitive to driving compared to idling, in either case, cold starts contribute substantially to total exhaust mass emissions. Furthermore, driver decisions regarding driving versus idle can substantially affect the contribution of cold starts, especially for CO and NOx.

Real Driving Emission from Vehicle Fuelled by Petrol and Liquefied Petroleum Gas (LPG)

In recent years, in addition to laboratory tests to determine emissions from road motor vehicles, tests in real driving conditions RDE (Real Driving Emissions) with the use of portable measuring equipment PEMS (Portable Emissions Measurement System) have been conducted. The paper presents the results of the emission research conducted on a vehicle Dacia Duster 1.0 TCe 100 ECO-G fuelled by petrol Eurosuper 95 and liquefied petroleum gas (LPG). The aim of the research was to determine the emissions of harmful substances and carbon dioxide, i.e. fuel consumption, in accordance with the prescribed RDE procedure and their comparison for the two types of motor vehicle fuel. Results clearly showed that the method used can differentiate between fuel types. The results correspond to the RDE emissions public data, which secures that the methodology used is in accordance with the procedure for measuring emissions in real driving conditions.

Characteristics of Real-World Gaseous Emissions from Construction Machinery

In Korea’s air pollutant inventory, construction machinery is a major emission source in the non-road sector. Since 2004, the Korean government has introduced and reinforced emission regulations to reduce the air pollutants emitted from their diesel engines. Since the engine dynamometer test method used in emission regulations has limitations in reflecting emission characteristics under the diverse working conditions of construction machinery, it is necessary to examine the effectiveness of emission regulations and the validity of the emission factors applied as inputs to the air pollutants inventory. This could be done by evaluating engine operation and emission characteristics under real-world working conditions. In this study, 14 units were selected among the excavators, wheel loaders, and forklifts that represent approximately 90% of the registered construction machines in Korea. They were equipped with a portable emission measurement system (PEMS) to measure gaseous emissions and collect engine data under various real-world working conditions. With the reinforcement of emission regulations for the construction machinery from K-tier3 to K-tier4 in Korea, exhaust after-treatment technologies, such as selective catalytic reduction and diesel oxidation catalyst, were applied. Real world NOx was reduced by approximately 83%, and THC 77% and CO by 73%, respectively. Real world NOx + THC of the K-tier3 machines exceeded the laboratory emission limit, but the K-tier4 machines considerably improved, 20% for excavator (124 kW), 61% for excavator (90 kW), 90% for wheel loader (202 kW) and 21% for Fork-lift (55 kW), despite some differences. The emission factors applied to the air pollutant inventory have been developed using the engine dynamometer test method, but they were considerably underestimated compared with emissions under real-world working conditions. The difference was even larger for the K-tier4 machines. In this study, the possibility of developing emission factor equations that use the engine load factor as a parameter was confirmed by using the engine work 1 g/kW·h segment moving averaging window (MAW) method.

Influence of Driving Cycles on Emission Parameters of Vehicles

The vehicle emissions tests, which are performed using the Portable Emissions Measurement Systems (PEMS), indicate that the diesel cars produce several times more NOx emissions on the road than during certification realised according to the methodology New European Driving Cycle (NEDC). This fact initiated the infamous "dieselgate" affair. It is a well-known reality that the current emission limits are very strict and therefore a serious problem arises for the motor car producers to meet the demanding emission requirements. The main task of the presented research work was testing of 10 passenger cars with regard to true values of their exhaust gas emissions. These cars were equipped with the diesel engines and gasoline engines that officially meet the Euro 4-6 standards. Based on the measured results it was found that the real NOx emissions of the diesel engines significantly exceed the values measured by NEDC. The results obtained using the NEDC cycle also contradict the findings from two alternative driving cycles: CADC (Common Artemis Driving Cycle; Artemis - Assessment and Reliability of Transport Emission Models and Inventory Systems) and WLTC (Worldwide harmonized Light vehicles Test Cycle).

Real driving emissions of Euro 6 electric/gasoline hybrid and natural gas vehicles

Electric hybrid powertrain and natural gas fuel for spark-ignition engines are among the much promising technologies to reduce the fossil fuel use for road transportation and the emissions of harmful and greenhouse gases. This paper investigated gas and particulate real emissions of hybrid and natural gas passenger cars. On road testing were carried out along urban, rural and motorway routes in Napoli (Italy), by using portable emissions measurement systems. Hybrid vehicle has the main advantage of fuel saving in urban environment due to large use of pure electric mode operation at low speed and load. On the other hand, continuous engine restarting causes peak emissions due to a longer light-off time of aftertreatment systems. By analysing the Vehicle Specific Power, it was observed that at same positive values of power, natural gas vehicle is characterized by lower emission and fuel/energy consumption rates compared to the hybrid vehicle.

Real-Time Measurement of NOx Emissions from Modern Diesel Vehicles Using On-Board Sensors

In this work, the performance of on-board vehicle exhaust emission sensors is investigated and compared to reference laboratory and on-road instrumentation for two modern diesel light-duty commercial vehicles, type-approved as Euro 6d-TEMP-EVAP-ISC and Euro 6d-ISC-FCM. The first step of the analysis was to perform emissions tests in the laboratory and compare the NOx concentrations registered by the vehicle sensors available at the engine-out and tailpipe positions with those recorded by reference laboratory instrumentation. In a second step, tests were also conducted on road, comparing the performance of on-board sensors with those of Portable Emission Measurement System (PEMS) analysers, which were taken as references. The uncertainty related to exhaust flow measurements was also addressed. In particular, emissions factors calculated using the flow rates measured either in the laboratory or on-road were compared to those obtained by computing exhaust flows with on-board recorded data available from the vehicle electronic control unit. Results showed maximum deviations on the order of 34% in laboratory tests and of 21% during on-road measurements. Finally, measurements were also carried out during a diesel particulate filter regeneration event, showing the good performance of the on-board sensors even when high NOx concentrations were present. These conditions can be similar to those experienced in the case of an after-treatment system malfunction or of a high-emitting event, and can thus be of interest for real-time malfunction identification and monitoring.