A review on morphology, nanostructure, chemical composition, and number concentration of diesel particulate emissions

Insight into the mechanism of solution organic fractions on soot oxidation activity enhancement

The particulate matter and soluble organic fraction emitted by diesel engine are hazardous to environment and human health. Exploring the effect mechanism of soluble organic fraction on soot oxidation is beneficial for reducing the emissions. In this study, the effects of four different types of soluble organic fractions on the soot oxidation activity and physicochemical properties are investigated. The results show that the attachment of oxygen-containing soluble organic fractions enhances the soot oxidation and reduces the peak characteristic temperature. However, the low volatility soluble organic fractions without oxygen element inhibit soot oxidation. Additionally, the high volatility soluble organic fractions without oxygen element elicit limited effects on soot oxidation. the contents of aliphatic C-H functional groups, carbonyl CO functional groups, and carboxylic acid O-CO functional groups significantly increase after adding oxygen-containing soluble organic fractions, while the limited increase in functional groups is observed in soluble organic fractions without oxygen element. Solid soluble organic fractions adhere to soot particles in the form of small particles, leading a reduction in the initial particle size distribution, while liquid soluble organic fractions exhibit block and chain shapes around the soot particles, which makes the initial particle size distribution increasing. Moreover, the attachment of all soluble organic fractions disrupts the surface order of soot particle, leading to a decrease in soot graphitization. This study is beneficial for revealing the interaction mechanism between soot and soluble organic fractions.

Chemical characteristics of fine tire wear particles generated on a tire simulator

Tire wear is one of the major sources of traffic-related particle emissions, however, laboratory data on the components of tire wear particles (TWPs) is scarce. In this study, ten brands of tires, including two types and four-speed grades, were chosen for wear tests using a tire simulator in a closed chamber. The chemical components of PM2.5 were characterized in detail, including inorganic elements, water-soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), and polycyclic aromatic hydrocarbons (PAHs). Inorganic elements, WSIs, OC, and EC accounted for 8.7 ± 2.1%, 3.1 ± 0.7%, 44.0 ± 0.9%, and 9.6 ± 2.3% of the mass of PM2.5, respectively. The OC/EC ratio ranged from 2.8 to 7.6. The inorganic elements were dominated by Si and Zn. The primary ions were SO42- and NO3-, and TWPs were proven to be acidic by applying an ionic balance. The total PAHs content was 113 ± 45.0 μg g-1, with pyrene being dominant. In addition, the relationship between the chemical components and tire parameters was analyzed. Inorganic elements and WSIs in TWPs were more abundant in all-season tires than those in winter tires, whereas the content of PAHs was the opposite. The mass fractions of OC, Si, and Al in the TWPs all showed increasing trends with increasing tire speed grade, but the PAHs levels showed a decreasing trend. Ultimately, to provide more data for further research, a TWPs source profile was constructed considering the tire weighting factor.

Urban dust particles disrupt mitotic progression by dysregulating Aurora kinase B-related functions

Particulate matter (PM), a major component of outdoor air pollution, damages DNA and increases the risk of cancer. Although the harmful effects of PM at the genomic level are known, the detailed mechanism by which PM affects chromosomal stability remains unclear. In this study, we investigated the novel effects of PM on mitotic progression and identified the underlying mechanisms. Gene set enrichment analysis of lung cancer patients residing in countries with high PM concentrations revealed the downregulation of genes associated with mitosis and mitotic structures. We also showed that exposure of lung cancer cells in vitro to urban dust particles (UDPs) inhibits cell proliferation through a prolonged M phase. The mitotic spindles in UDP-treated cells were hyperstabilized, and the number of centrioles increased. The rate of ingression of the cleavage furrow and actin clearance from the polar cortex was reduced significantly. The defects in mitotic progression were attributed to inactivation of Aurora B at kinetochore during early mitosis, and spindle midzone and midbody during late mitosis. While previous studies demonstrated possible links between PM and mitosis, they did not specifically identify the dysregulation of spatiotemporal dynamics of mitotic proteins and structures (e.g., microtubules, centrosomes, cleavage furrow, and equatorial and polar cortex), which results in the accumulation of chromosomal instability, ultimately contributing to carcinogenicity. The data highlight the novel scientific problem of PM-induced mitotic disruption. Additionally, we introduce a practical visual method for assessing the genotoxic outcomes of airborne pollutants, which has implications for future environmental and public health research.

Effect of regeneration method and ash deposition on diesel particulate filter performance: a review

As countries around the world pay more attention to environmental protection, the corresponding emission regulations have become more stringent. Exhaust pollutants cause great harm to the environment and people, and diesel engines are one of the most important sources of pollution. Diesel particulate filter (DPF) technology has proven to be the most effective way to control and treat soot. In this paper, we review the latest research progress on DPF regeneration and ash. Passive regeneration, active regeneration, non-thermal plasma-assisted DPF regeneration and regeneration mechanism, DPF regeneration control assisted by engine management, and uncontrolled DPF regeneration and its control strategy are mainly introduced. In addition, the source, composition, and deposition of ash are described in detail, as well as the effect of ash on the DPF pressure drop and catalytic performance. Finally, the issues that need to be further addressed in DPF regeneration research are presented, along with challenges and future work in ash research. Over all, composite regeneration is still the mainstream regeneration method. The formation of ash is complex and there are still many unanswered questions that require further in-depth research.

Chemical characterization of combustion engine exhaust and assessment of helicopter deck operator occupational exposures on an offshore frigate class ship

Diesel engine exhaust (DE) consists of a complex mixture of gases and aerosols, originating from sources such as engines, turbines, and power generators. It is composed of a wide range of toxic compounds ranging from constituents that are irritating to those that are carcinogenic. The purposes of this work were to characterize DE originating from different engine types on a ship operating offshore and to quantify the potential exposure of workers on the ship's helicopter deck to select DE compounds. Sampling was conducted on a Norwegian Nansen-class frigate that included helicopter operations. Frigate engines and generators were fueled by marine diesel oil, while the helicopter engine was fueled by high flash point kerosene-type aviation fuel. Exhaust samples were collected directly from the stack of the diesel engine and one of the diesel generator exhaust stacks, inside a gas turbine exhaust stack, and at the exhaust outlet of the helicopter. To characterize the different exhaust sources, non-targeted screening of volatile and semi-volatile organic compounds was performed for multiple chemical classes. Some of the compounds detected at the sources are known irritants, such as phthalic anhydride, 2,5-dyphenyl-p-benzoquinone, styrene, cinnoline, and phenyl maleic anhydride. The exhaust from the diesel engine and diesel generator was found to contain the highest amounts of particulate matter and gaseous compounds, while the gas turbine had the lowest emissions. Personal exposure samples were collected outdoors in the breathing zone of a helicopter deck operator over nine working shifts, simultaneously with stationary measurements on the helicopter deck. Elemental carbon, nitrogen dioxide, and several volatile organic compounds are known to be present in DE, such as formaldehyde, acrolein, and phenol were specifically targeted. Measured DE exposures of the crew on the helicopter deck were variable, but less than the current European occupational exposure limits for all compounds, except elemental carbon, in which concentration varied between 0.5 and 37 µg/m³ over nine work shifts. These findings are among the first published for this type of working environment.

Role of Secondary Organic Matter on Soot Particle Toxicity in Reconstituted Human Bronchial Epithelia Exposed at the Air-Liquid Interface

Secondary organic matter (SOM) formed from gaseous precursors constitutes a major mass fraction of fine particulate matter. However, there is only limited evidence on its toxicological impact. In this study, air-liquid interface cultures of human bronchial epithelia were exposed to different series of fresh and aged soot particles generated by a miniCAST burner combined with a micro smog chamber (MSC). Soot cores with geometric mean mobility diameters of 30 and 90 nm were coated with increasing amounts of SOM, generated from the photo-oxidation of mesitylene and ozonolysis of α-pinene. At 24 h after exposure, the release of lactate dehydrogenase (LDH), indicating cell membrane damage, was measured and proteome analysis, i.e. the release of 102 cytokines and chemokines to assess the inflammatory response, was performed. The data indicate that the presence of the SOM coating and its bioavailability play an important role in cytotoxicity. In particular, LDH release increased with increasing SOM mass/total particle mass ratio, but only when SOM had condensed on the outer surface of the soot cores. Proteome analysis provided further evidence for substantial interference of coated particles with essential properties of the respiratory epithelium as a barrier as well as affecting cell remodeling and inflammatory activity.

Dissociation characteristics and anthropogenic emissions from the combustion of double gas hydrates

Gas hydrates are an alternative and environmentally friendly energy source increasingly in the focus of scientific attention. The physicochemical processes behind gas hydrate combustion are studied experimentally and numerically with a view to improving the combustion efficiency and reducing gas emissions. It is important to estimate the pollutant emission concentrations in the context of combustion conditions. The research deals with the dissociation and combustion behavior of double gas hydrates in a tubular muffle furnace. Gas hydrates of different composition are considered: methane, methane-ethane, methane-propane and methane-isopropanol. Double gas hydrates are characterized by more stable combustion compared to methane hydrate. It is also shown that the double gas hydrate dissociation rate increases by 15-30% with increasing temperature. Dissociation and combustion processes were also modeled as part of the research, accounting for phase transitions in a gas hydrate layer. According to the simulation results, the total dissociation rate of gas hydrate increases by 3 times with an about 2.5-times increase in the powder layer thickness. Our experiments also focused on the impact of furnace temperature and gas hydrate composition on concentrations of anthropogenic gas emissions. We have found that the presence of heavy hydrocarbons such as ethane, propane and isopropanol in double gas hydrates reduce unburned CH₄ emissions by 60%. Also, an increase in the combustion efficiency of double gas hydrates, accompanied by a decrease in the concentrations of unburned CH₄ and CO, affects the yield of CO₂, which increased by 13-35%. When we increased the temperature in the furnace from 750 °C to 1050 °C, concentrations of nitrogen oxides and carbon dioxide increased by up to five times. Thus, the resulting correlations between the key parameters of these processes and a set of the main inputs illustrate the possibility to predict the optimal conditions for the combustion of gas hydrates.