Panagiota Dilara

Microplastics pollution is becoming a major environmental concern for air, soil, and water. The European Union (EU) Zero Pollution Action Plan targets to reduce microplastics release to the environment by 30% by 2030. Tyre wear is estimated to be the most important contributor to unintentionally released microplastics to the environment. For this reason, the new Euro 7 vehicle emission standard introduced placeholders for limiting tyre abrasion. In this study, we calculate the environmental pollution from tyres using as a basis a recent review on tyre wear emission factors. We also estimate the impact of reducing the average emission factors following the Euro 7 implementation dates. Additionally, we present the cost savings to the EU by such a reduction over a time horizon until 2050. Even though the final cost saving estimations come with some uncertainty due to lack of accurate and up-to-date emission factors, especially for heavy-duty vehicles, the introduction of tyre wear limits has a significant positive impact under all scenarios examined.

On-road real-driving emissions (RDE) tests with portable emissions measurement systems (PEMS) are part of the vehicle emissions regulations in the European Union (EU). For a given vehicle, the final emission results depend on the influence of the ambient conditions and the trip characteristics (including the driver’s behaviour) on the vehicle performance and the instrument measurement uncertainty. However, there are not many studies that have examined the emissions variability of a single vehicle following different routes. In this study, a 1.2 L gasoline direct injection (GDI) Euro 5b passenger car without a particulate filter and a PEMS was circulated in seven European laboratories. At their premises, the laboratories performed two to five repetitions of on-road trips compliant with the EU RDE regulation. The ambient temperature ranged between 7 °C and 23 °C. The average emission levels of the vehicle were 135 g/km for CO₂, 77 mg/km for CO, 55 mg/km for NO_x, and 9.2 × 10¹¹ #/km for particle number. The coefficient of variance in the emissions following the same route was 2.9% for CO₂, 23.8% for CO, 23.0% for NO_x, and 5.8% for particle number. The coefficient of variance in the emissions following different routes in Europe was 6.9% for CO₂, 9.1% for CO, 0.0% for NO_x, and 9.1% for particle number. The previous values include the specific vehicle emissions variability under the narrow test conditions of this study, but only partly the PEMS measurement uncertainty because the same instrument was used in all the trips. The results of this study can be used by laboratories conducting RDE tests to assess their uncertainty budget when testing or comparing vehicles of similar technology.

Particulate Matter (PM) air pollution has been linked to major adverse health effects. Road transport still contributes significantly to ambient PM concentrations, but mainly due to the non-exhaust emissions from vehicles. For the first time worldwide, limits for non-exhaust emissions have been proposed by the European Union for the upcoming Euro 7 step. For these reasons, interest in brake emissions has increased in the past few years. Realistic emission factors are necessary to accurately calculate the contribution of brake emissions to air pollution but also to estimate the emissions reduction potential of new or existing technologies and improved brake formulations. This paper reviews emission factors from light-duty vehicles reported in the literature, with a focus on those that followed the recently introduced Global Technical Regulation (GTR 24) methodology on brakes in light-duty vehicles. Reduction efficiencies of non-asbestos organic (NAO) pads, brake dust filters, ceramic discs, coated discs, and regenerative braking are also discussed. Finally, the emission factors are compared with roadside measurements of brake emissions and emission inventories worldwide. The findings of this study can be used as an input in emission inventories to estimate the contribution of brakes to air pollution.

Tyre particles are generated by shear forces between the tread and the road or by volatilisation. Tyre abrasion (wear) contributes from one-third to half of microplastics unintentionally released into the environment. The major part ends up in the soil, a considerable amount is released into the aquatic environment, and a small percentage becomes airborne. Nevertheless, tyre abrasion contributes to 5–30% of road transport particulate matter (PM) emissions. This corresponds to approximately 5% of total ambient PM emissions. The particle mass size distribution peak at around 20 to 100 μm, with a second peak in the 2–10 μm range. A nucleation mode has been reported in some studies. The absolute abrasion levels depend on the tyre, vehicle, and road characteristics, but also on environmental conditions and driving style. Most tyre particle emission factors in the literature are based on data prior to the year 2000. We aggregated recent studies and found a mean abrasion of 110 mg/km per vehicle or 68 mg/km/t for passenger cars (based on approximately 300 measurements). Based on a limited number of studies, the PM₁₀ emissions were 1.4–2.2 mg/km per tyre. On the other hand, the particle number emissions were in the order of 10¹⁰ #/km per tyre. The ratio of PM₁₀ to total abrasion was found to be 2.5% on average. Finally, the ratio of PM_2.5 to PM₁₀ was calculated to be around 40%. Various mitigation measures for tyre particle pollution could be envisaged; the most direct is the limitation of the tyre abrasion rate, as proposed by the European Commission for the Euro 7 regulation. Other regulatory initiatives are also discussed.

Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH₃, SO_x), or revision of fuel and lubricant specifications.

Vehicle emissions are a significant source of air pollution in cities. Particulate matter (PM) is a pollutant with adverse health effects. Regulations worldwide determine the PM exhaust emissions of vehicles by gravimetric quantification of the mass deposited on a filter over a test cycle. The introduction of particulate filters as vehicle exhaust gas aftertreatment devices led to low PM emissions. A particle number methodology (counting solid particles > 23 nm), complementary to the PM mass measurement, was developed by the PMP (Particle Measurement Programme) group of the GRPE (Working Party on Pollution and Energy) of the UNECE (United Nations Economic Commission for Europe) during the first decade of the 21st century. The methodology was then introduced in the EU (European Union) regulations for light-duty (2011), heavy-duty (2013), and non-road mobile machinery (2019). In parallel, during the last 15 years, UN (United Nations) regulations and GTRs (Global Technical Regulations) including this methodology were also developed. To address the on-road emissions, the EU introduced RDE (real-driving emissions) testing with PEMS (portable emissions measurement systems) in 2017. Other countries (e.g., China, India) have also started adopting the number methodology. The PMP group recently improved the current laboratory and on-board methodologies and also extended them to a lower particle size (counting solid particles > 10 nm). Due to the rapid evolution of the vehicle exhaust particle number regulations and the lack of a summary in the literature, this paper gives an overview of current and near future regulations. Emphasis is given on the technical specifications and the changes that have taken place over the years.

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.

With the introduction of gasoline particulate filters (GPFs), the particle number (PN) emissions of gasoline direct-injection (GDI) vehicles are below the European regulatory limit of 6 × 10¹¹ p/km under certification conditions. Nevertheless, concerns have been raised regarding emission levels at the boundaries of ambient and driving conditions of the real-driving emissions (RDE) regulation. A Euro 6d-Temp GDI vehicle with a GPF was tested on the road and in the laboratory with cycles simulating congested urban traffic, dynamic driving, and towing a trailer uphill at 85% of maximum payload. The ambient temperatures covered a range from −30 to 50 °C. The solid PN emissions were 10 times lower than the PN limit under most conditions and temperatures. Only dynamic driving that regenerated the filter passively, and for the next cycle resulted in relatively high emissions although they were still below the limit. The results of this study confirmed the effectiveness of GPFs in controlling PN emissions under a wide range of conditions.

Portable emissions measurement systems (PEMS) for gaseous pollutants were firstly introduced in the United States regulation to check the in-use compliance of heavy-duty engines, avoiding the high costs of removing the engine and testing it on a dynamometer in the laboratory. In Europe, the in-service conformity of heavy-duty engines has been checked with PEMS for gaseous pollutants since 2014. To strengthen emissions regulations with a view to minimise the differences between on-road and laboratory emission levels in some cases, PEMS testing, including solid particle number (SPN), was introduced for the type-approval of light-duty vehicles in Europe in 2017 and for in-service conformity in 2019. SPN-PEMS for heavy-duty engines will be introduced in 2021. This paper gives an overview of the studies for SPN-PEMS from early 2013 with the first prototypes until the latest testing and improvements in 2019. The first prototype diffusion charger (DC) based systems had high differences from the reference laboratory systems at the first light-duty vehicles campaign. Tightening of the technical requirements and improvements from the instrument manufacturers resulted in differences of around 50%. Similar differences were found in an inter-laboratory comparison exercise with the best performing DC- and CPC- (condensation particle counter) based system. The heavy-duty evaluation phase at a single lab and later at various European laboratories revealed higher differences due to the small size of the urea generated particles and their high charge at elevated temperatures. This issue, along with robustness at low ambient temperatures, was addressed by the instrument manufacturers bringing the measurement uncertainty to the 50% levels. This measurement uncertainty needs to be considered at the on-road emission results measured with PEMS.

The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the market due to their improved efficiency over port fuel injection (PFI) ones. However, the PM mass and number emissions of GDI vehicles were higher than their PFI counterparts and diesel ones equipped with DPFs. Stringent PM mass levels and the introduction of particle number limits for GDI vehicles in the European Union (EU) resulted in significant PM reductions. The EU requirement to fulfill the proposed limits on the road resulted to the introduction of gasoline particulate filters (GPFs) in EU GDI models. This review summarizes the evolution of PM mass emissions from gasoline vehicles placed in the market from early 1990s until 2019 in different parts of the world. The analysis then extends to total and nonvolatile particle number emissions. Care is given to reveal the impact of ambient temperature on emission levels. The discussion tries to provide scientific input to the following policy-relevant questions. Whether particle number limits should be extended to gasoline PFI vehicles, whether the lower limit of 23 nm for particle number measurements should be decreased to 10 nm, and whether low ambient temperature tests for PM should be included.