Towards zero pollution vehicles by advanced fuels and exhaust aftertreatment technologies

Vehicular emissions deteriorate air quality in urban areas notably. The aim of this study was to conduct an in-depth characterization of gaseous and particle emissions, and their potential to form secondary aerosol emissions, of the cars meeting the most recent emission Euro 6d standards, and to investigate the impact of fuel as well as engine and aftertreatment technologies on pollutants at warm and cold ambient temperatures. Studied vehicles were a diesel car with a diesel particulate filter (DPF), two gasoline cars (with and without a gasoline particulate filter (GPF)), and a car using compressed natural gas (CNG). The impact of fuel aromatic content was examined for the diesel car and the gasoline car without the GPF. The results showed that the utilization of exhaust particulate filter was important both in diesel and gasoline cars. The gasoline car without the GPF emitted relatively high concentrations of particles compared to the other technologies but the implementation of the GPF decreased particle emissions, and the potential to form secondary aerosols in atmospheric processes. The diesel car equipped with the DPF emitted low particle number concentrations except during the DPF regeneration events. Aromatic-free gasoline and diesel fuel efficiently reduced exhaust particles. Since the renewal of vehicle fleet is a relatively slow process, changing the fuel composition can be seen as a faster way to affect traffic emissions.Peer reviewe

Lung-depositing surface area (LDSA) of particles in office spaces around Europe : Size distributions, I/O-ratios and infiltration

Air pollution, and specifically particulate matter pollution, is one of the greatest dangers to human health. Outdoor air pollution ranks third in causes for premature death. Improving indoor air quality is of immense importance, as the time spent indoors is often much greater than the time spent outdoors. In this experimental study, we evaluate the levels of particle pollution in indoor air in four offices across Europe, compare the indoor particles to outdoor particles and assess where the particles originate from. The measurements were conducted with an Electrical Low-Pressure Impactor (ELPI+) for particles between 6 nm and 1 μm. The chosen metric, lung-deposited particle surface area (LDSA), targets the health impacts of particle pollution. Based on the measurements, we determined that most of the indoor air particles infiltrated from outdoor air, although two of the offices had very limited indoor activity during the measurement campaigns and may not represent typical use. The highest median indoor LDSA concentration during daytime hours was 27.2 μm2/cm3, whereas the lowest was 2.8 μm2/cm3. Indoor air in general had lower LDSA concentrations than outdoor air, the corresponding outdoor LDSA concentrations being 35.8 μm2/cm3 and 9.8 μm2/cm3. The particle size ranges which contributed to the highest concentrations were 50–100 nm and 300–500 nm. These size ranges correspond to soot mode and accumulation mode particles, which represent local and regional sources, respectively. Based on this study, limiting particle infiltration is the key factor in keeping indoor air in offices free of lung-depositing particles.Peer reviewe

Electrofuel Concept of Diesel and Oxygenate Fuels Reduces Engine-Out Emissions

Electrofuels produced from renewable hydrogen (H2) and captured carbon dioxide (CO2) can be sustainable and carbon-neutral. Paraffinic electrodiesel (e-diesel) can be produced via Fischer-Tropsch synthesis with fuel properties resembling hydrotreated vegetable oils. Electrofuels can be also oxygenated compounds, such as oxymethylene dimethyl ethers (OMEn), having different chain lengths. We studied emissions using paraffinic diesel mimicking e-diesel and its blend with 10% of OME3-5, which has diesel-type fuel properties, in comparison with normal EN590 diesel fuel. An intensive measurement campaign was performed with a modern diesel engine without exhaust aftertreatment to study the effect of fuel on the engine-out emissions. Measurements with the RMC-C1 cycle included detailed characterization of gaseous, particle and polyaromatic hydrocarbon (PAH) emissions having adverse effects on health and the environment. In these tests without a diesel particulate filter, the fuel containing the OME3-5 component reduced the black carbon (BC) emissions substantially in comparison with EN590. PM and PAH emissions, as well as the number of non-volatile particle numbers (nvPN), were lower for paraffinic fuel than for the EN590 fuel, and particularly for the OME3-5 blend. As regards gaseous emissions, paraffinic fuel showed lower engine-out NOx emissions than the EN590 fuel, however, OME3-5 oxygenate did not further increase this NOx reduction. Higher formaldehyde concentration in the exhaust was found for OME3-5 containing fuel than for the hydrocarbon-only fuels, which can be tackled with an inexpensive oxidation catalyst. In summary, e-diesel type paraffinic fuel reduced the engine-out exhaust emissions from a modern diesel engine substantially, and OME3-5 addition further reduced the most harmful emission species even at a 10% blending level

Immersion freezing ability of freshly emitted soot with various physico-chemical characteristics

The immersion freezing ability of soot particles has in previous studies been reported in the range of low/insignificant to very high. The aims of this study were to: (i) perform detailed physico-chemical characterisation of freshly produced soot particles with very different properties, (ii) investigate the immersion freezing ability of the same particles, and (iii) investigate the potential links between physico-chemical particle properties and ice-activity. A miniCAST soot generator was used to produce eight different soot samples representing a wide range of physico-chemical properties. A continuous flow diffusion chamber was used to study each sample online in immersion mode over the temperature (T) range from −41 to −32◦C, at a supersaturation of about 10% with respect to liquid water. All samples exhibited low to no heterogeneous immersion freezing. The most active sample reached ice-activated fractions (AF) of 10−3 and 10−4 at temperatures of 1.7 and 1.9 K, respectively, above the homogeneous freezing temperature. The samples were characterized online with respect to a wide range of physico-chemical properties including effective particle density, optical properties, particle surface oxidation and soot maturity. We did observe indications of increasing immersion freezing ice-activity with increasing effective particle density and increasing particulate PAH fraction . Hence, those properties, or other properties co-varying with those, could potentially enhance the immersion freezing ice-activity of the studied soot particle types. However, we found no significant correlation between the physico-chemical properties and the observed ice-nucleating ability when the particle ensemble was extended to include previously published results including more ice-active biomass combustion soot particles. We conclude that it does not appear possible in general and in any straightforward way to link observed soot particle physico-chemical properties to the ice-nucleating ability using the online instrumentation included in this study. Furthermore, our observations support that freshly produced soot particles with a wide range of physico-chemical properties have low to insignificant immersion freezing ice-nucleating ability

Exhaust emissions from a prototype non-road natural gas engine

Since gas engines are considered a future solution to improve air quality and to mitigate climate impacts, there is an urgent need to understand their emissions. The aim for this study was to understand the phenomena affecting the formation of particulate emissions of a non-road natural gas engine. To achieve this, the engine's exhaust emissions were characterized under different operating conditions. The regulated pollutants (gaseous CO, HC, and NOx; particulate matter (PM) and particle number (PN)) were determined experimentally and a detailed characterization of particulate pollutants over a wide particle size range (particles down to 1.2 nm) was conducted with state-of-the-art instrumentation considering both physical and chemical properties of the exhaust aerosol. The test engine was a prototype non-road spark-ignited natural gas engine, which was studied over the non-road steady test cycle (NRSC). The role of the three-way catalyst (TWC) was studied by sampling and characterizing the exhaust aerosol both with and without the TWC. The TWC was observed to efficiently remove the vast majority of the regulated gaseous (96% CO, 98% HC, 98% NOx) and particulate mass emissions (98%). In general, the measured particle number emission factors were highly dependent on the cut-off sizes of the condensation particle counters. Using CPCs with smaller cut-off sizes resulted in higher particle number emission factors. For black carbon (BC), the intermediate engine speed conditions (modes 5–7) led to lower BC emissions than the high speed conditions (modes 1–3). In contrast, highest BC emissions on a work basis were observed during idling. TWC did not influence BC levels. Without the TWC, PM was comprised mostly of organic compounds (70–100%). Downstream of the TWC, the majority of PM was, depending on the load, composed of organic compounds, sulfate, or black carbon. A statistical source apportionment based on mass spectra revealed that the PM1 was mostly related to unburned and burned lubricating oil, indicating a minor role of fuel in PM formation.publishedVersionPeer reviewe

Snapshots of wintertime urban aerosol characteristics : local sources emphasized in ultrafine particle number and lung deposited surface area

Urban air fine particles are a major health-relating problem. However, it is not well understood how the healthrelevant features of fine particles should be monitored. Limitations of PM2.5 (mass concentration of sub 2.5 μm particles), which is commonly used in the health effect estimations, have been recognized and, e.g., World Health Organization (WHO) has released good practice statements for particle number (PN) and black carbon (BC) concentrations (2021). In this study, a characterization of urban wintertime aerosol was done in three environments: a detached housing area with residential wood combustion, traffic-influenced streets in a city centre and near an airport. The particle characteristics varied significantly between the locations, resulting different average particle sizes causing lung deposited surface area (LDSA). Near the airport, departing planes had a major contribution on PN, and most particles were smaller than 10 nm, similarly as in the city centre. The high hourly mean PN (>20 000 1/cm3) stated in the WHO’s good practices was clearly exceeded near the airport and in the city centre, even though traffic rates were reduced due to a SARS-CoV-2-related partial lockdown. In the residential area, wood combustion increased both BC and PM2.5, but also PN of sub 10 and 23 nm particles. The high concentrations of sub 10 nm particles in all the locations show the importance of the chosen lower size limit of PN measurement, e.g., WHO states that the lower limit should be 10 nm or smaller. Furthermore, due to ultrafine particle emissions, LDSA per unit PM2.5 was 1.4 and 2.4 times higher near the airport than in the city centre and the residential area, respectively, indicating that health effects of PM2.5 depend on urban environment as well as conditions, and emphasizing the importance of PN monitoring in terms of health effects related to local pollution sources

Particle emissions from a modern heavy-duty diesel engine as ice nuclei in immersion freezing mode : A laboratory study on fossil and renewable fuels

We studied ice-nucleating abilities of particulate emissions from a modern heavy-duty diesel engine using three different types of fuel. The polydisperse particle emissions were sampled during engine operation and introduced to a continuous-flow diffusion chamber (CFDC) instrument at a constant relative humidity RHwater 110%, while the temperature was ramped between-43 and-32 C (T scan). The tested fuels were EN 590 compliant low-sulfur fossil diesel, hydrotreated vegetable oil (HVO), and rapeseed methyl ester (RME); all were tested without blending. Sampling was carried out at different stages in the engine exhaust aftertreatment system, with and without simulated atmospheric processing using an oxidation flow reactor. In addition to ice nucleation experiments, we used supportive instrumentation to characterize the emitted particles for their physicochemical properties and presented six parameters. We found that the studied emissions contained no significant concentrations of ice-nucleating particles likely to be of atmospheric relevance. The substitution of fossil diesel with renewable fuels, using different emission aftertreatment systems such as a diesel oxidation catalyst, and photochemical aging of total exhaust had only minor effect on their ice-nucleating abilities.publishedVersionPeer reviewe

Effects of fuel composition and vehicle operating temperature on in vitro toxicity of exhaust emissions

Traffic as an important part of the energy sector significantly contributes to global air pollution. To mitigate the hazardous components of traffic emissions regulations have been implemented resulting in technological solutions such as exhaust after-treatment systems. However, fuels also play a crucial role in emissions and components such as the aromatic compounds in fuel have been linked to increased exhaust emissions. Several current emissions regulations neglect environmental factors, such as cold operating temperatures, that can significantly increase emissions. Moreover, the effect of fuel aromatics and cold temperature on emissions toxicity has not been adequately studied. This study evaluates the impact of after-treatment systems, aromatic fuel content, and cold operating temperature on emission toxicity. To achieve this, four different light-duty vehicles were used in a temperature-controlled dynamometer room, with a co-culture of A549 and THP-1 cell lines exposed to online exhaust emissions using a thermophoresis-based air-liquid interface (ALI) system. The results demonstrate that the aromatic content of both diesel and gasoline fuels increases exhaust toxicity. The study additionally emphasises the potential of particulate filters as after-treatment systems to reduce the toxicity of emissions and highlights how cold running temperatures result in higher exhaust toxicity. The study also assessed the diesel particulate filter (DPF) active regeneration event, which leads to multi-fold emissions and higher toxicological responses. Overall, the study provides crucial novel results on how various factors affect the toxicity of exhaust emissions from modern light-duty vehicles, providing insights into decreasing the emissions from this energy sector.Peer reviewe