Soot Particles Research Articles

Characterization of soot and crystalline atmospheric ultrafine particles.

The extraction and characterization of atmospheric ultrafine particles (UFPs) is critical to understanding environmental health and climate dynamics. This study uses an aqueous extraction method to characterize the size distribution, shape, and composition of atmospheric UFPs. We propose a combined use of techniques rarely implemented in air quality analysis, such as atomic force microscopy (AFM), with more conventional methods, such as Transmission Electron microscopy (TEM) and Dynamic Light Scattering (DLS). DLS results indicate a hydrodynamic diameter range from 117 to 1069 nm and a polydispersity index of 0.3 to 0.79. The high polydispersity reflects the complexity of UFPs agglomeration processes. AFM identified NPs ranging from 10 to 25 nm; topographic images show soot and crystalline structures. High-resolution TEM analysis measured the interplanar distances of crystalline UFPs, showing the presence of calcium carbonates. TEM-EDS identified soot and crystalline particles with variable composition, from Si-enriched NPs to Ca-F-Cl-Na-Si, carbonates, chlorides, and Zn-Ti-enriched nanosilica. These findings provide valuable insights into the physicochemical properties of atmospheric dust, contributing to our knowledge and the potential implications for human health and the environment.

Thermodynamic evaluation of contrail formation from a conventional jet fuel and an ammonia-based aviation propulsion system.

Condensation trail (contrail) formation in an airplane's wake requires thermodynamics supersaturation and ice nucleation to form visible ice crystals. Here, using a thermodynamic analysis, we evaluate the potential for forming contrails in a carbon-free, ammonia-powered propulsion system compared to conventional planes powered by jet fuel. The analysis calculates the moisture released by fuel into the atmosphere for each one-degree increase in air temperature due to exhaust gas. It then determines if this moisture can saturate the initially undersaturated atmosphere, maintain saturation as temperature rises, and result in supersaturation with respect to ice while leaving enough moisture for a visible cloud to form. With ammonia increases the critical temperature required for supersaturation. Although ammonia does not generate soot particles in the exhaust gas, various aerosols exist in the atmosphere through other sources that can facilitate heterogeneous ice nucleation. Hence, while ammonia's contrails might not be as dense, they can form at lower altitudes where the air is warmer and endure longer due to the increased water content, which preserves supersaturation for longer as fresh air dilutes the contrail.

Formation mechanism of soot in pyrolysis of 2-methylfuran under high temperature based on ReaxFF molecular dynamics simulation

In this study, the detailed mechanism of soot formation under high temperature pyrolysis of 2-methylfuran (2-MF) has been investigated by using Reactive force field molecular dynamics (ReaxFF MD) simulation. The MD analysis shows that 2-MF undergoes ring cleavage and the removal of CO/HCO/CH2CO/CH3CO, which results in the production of the C2-C4 species, promoting the formation of the initial ring molecules. The clustering of hydrocarbons by radical-chain reaction (CHRCR) mechanism plays a significant role in the mass growth of both polycyclic aromatic hydrocarbons (PAHs) and initial soot particles. The main contributors to this process are C2H2 and resonance-stabilized free radicals of C3 and C4. The H-abstraction-C2H2-addition (HACA) mechanism is important for the formation of surface active sites for PAHs and initial soot to some extent. In addition, the soot formation capacity of 2,5-dimethylfuran (25DMF) and 2-MF are compared. Under the same simulation conditions, 25DMF exhibits a higher capacity to form soot. Compared with 2-MF, 25DMF pyrolysis forms more ring-containing species at the initial stage, particularly cyclopentadiene and its derivatives. These compounds have the ability to promote the formation of PAHs, thus providing further support to the experimental-based theory.

Large eddy simulation of soot formation in a turbulent lifted flame with a discretized population balance and a reduced kinetic mechanism

This article presents simulations of a turbulent lifted flame using the large eddy simulation-transport probability density function-discretized population balance equation approach. This approach takes into account the interaction between turbulent reacting flow and soot particle formation. A reduced chemical kinetics mechanism including a series of polycyclic aromatic hydrocarbons (PAHs) species linked to soot formation is generated employing the approach of the directed relation graph error propagation and is tested on a perfectly stirred reactor under varying equivalent ratio conditions and premixed flames. The soot kinetics model includes the PAH-based nucleation and surface condensation, the hydrogen abstraction acetylene addition surface growth and oxidation mechanism, and the size-dependent aggregation. The soot morphology considers the surface area and other geometrical properties for both spherical primary particles and fractal aggregates. The simulation results show, in general, reasonably good agreement with experimental measurements in terms of lifted height, flame shape, flow-field velocity, the hydroxyl radical, and soot volume fraction. A discussion of micromixing and its modeling in the context of the Interaction by Exchange with the Mean model is also presented. To investigate the effect of the soot micromixing frequency factor on soot particles, an additional simulation is conducted where this factor is reduced by a factor of 10 for the soot particles. The maximum soot volume fraction is observed to increase slightly. However, compared with the impact of kinetics on soot modeling, this effect is a minor one.

Research on jet ignition phases and control parameters in an active pre-chamber optical engine under ultra-lean combustion conditions

The active pre-chamber (APC) jet ignition system is one of the primary technologies for achieving ultra-lean combustion and high thermal efficiency in engines. The impact of the jet process within the engine, as well as its control parameters, on emission pollutants (particularly soot particles) remains unclear. This study focuses on examining the effects of various low-flow injection control strategies on engine combustion and emissions by using optical experiments and numerical simulations. It also explores the impact of different ignition advance angles (ignition timings) based on a short pre-chamber mixing interval to observe ignition combustion, flame propagation, and emission characteristics under ultra-lean conditions (λ = 2.0). The main conclusions are as follows. Appropriately increasing the injection mass can enhance engine load. However, further increases in injection mass significantly raise particulate emissions, resulting in an increase in particle number by up to more than 37-fold, especially for small particles in the 5–––10 nm size range. The chemical reaction between the luminous jet flame and the bright incandescent wake jet flame, as captured by high-speed photography, effectively characterizes the various stages of jet ignition. To reduce particulate matter emissions, it is crucial to avoid the foreseeable wake jet flame caused by the enrichment of the jet mixture in the pre-chamber. The low-flow injection timing should neither be too early nor close to the ignition spark timing. The early injection causes fuel to accumulate at the top of the pre-chamber, hindering the jet flame’s propagation into the main combustion chamber. Late low-flow injection leads to fuel enrichment, resulting in uneven mixing and poor atomization and diffusion due to short mixing times. Ignition after a short mixing time interval tends to increase knocking, resulting in intense combustion and an advanced phase, which slightly reduces load and combustion stability. Regarding the heat release ratio, the total heat release from the two combustion stages in the pre-chamber should ideally account for about 5–6 % of the heat release in the main chamber.

Advancements in cobalt‐based oxide catalysts for soot oxidation: Enhancing catalytic performance through modification and morphology control

AbstractThe widespread use of diesel engines results in significant environmental contamination due to emitted pollutants, particularly soot particles. These pollutants are detrimental to public health. At present, one of the most effective ways to remove soot particles is the catalytic diesel particulate filter after‐treatment technology, which requires the catalyst to have superior low temperature activity. Compared with cerium oxide which is widely used, cobalt oxide in transition metal oxides has been widely studied in recent years because of its high redox ability and easy to control morphology. This paper elaborates on the influence of modification techniques such as doping, loading, and solid solution on the catalytic performance of cobalt‐based catalysts in soot oxidation. Along the same lines, it further reviews the research progress on cobalt‐based oxide catalysts with specific dimensional structures and morphologies in soot oxidation. Finally, it provides an outlook on the challenges faced by the theoretical basis and applied research of cobalt‐based catalysts in soot oxidation.

Virtual cleaning of sooty mural hyperspectral images using the LIME model and improved dark channel prior

Murals, as important carriers of cultural heritage and historical records, showcase artistic, aesthetic, social, and political significance. In ancient times, religious activities such as burning incense and candles in temples led to many murals being polluted by soot, causing them to darken, lose details, and, in severe cases, completely blacken. As a result, the development of efficient virtual cleaning methods has become a key strategy for addressing this issue. In this study, we use synthetic true colour and false colour images in different bands of the hyperspectral spectrum, and use a guided filter fusion technique to fuse these two images into a new image of the sooty mural. Through analyzing the histograms and colour distribution scatterplots of the synthetic sooty mural images, we observed significant similarities to low-luminance images. To enhance the synthesized murals, we applied the LIME model. In addition, comparisons of the histograms and colour distribution scatterplots of the enhanced sooty mural images with those of haze images revealed notable similarities. Therefore, we applied the dark channel prior algorithm to remove soot from the mural images. Considering that soot particles are larger than haze particles, we introduced guided filtering to refine the transmission map and created a nonlinear transformation function to enhance its details. In terms of both visual perception and quantitative analysis, the proposed method significantly outperforms previous methods in the virtual cleaning of sooty murals. This technology can not only restore the colours and details of murals but also provide new clues for subsequent mural studies, allowing people to once again appreciate the true beauty of the murals.

Coupling Effect of Elemental Carbon and Organic Carbon on the Changes of Optical Properties and Oxidative Potential of Soot Particles under Visible Light.

Soot particles, coming from the incomplete combustion of fossil or biomass fuels, feature a core-shell structure with inner elemental carbon (EC) and outer organic carbon (OC). Both EC and OC are known to be photoactive under solar radiation. However, research on their coupling effect during photochemical aging remains limited. This study examines how the optical properties and oxidative potential (OP) of wood, coal, and diesel soot particles with varying EC and OC levels are affected by exposure to visible light. Wood soot, which has the highest OC content, showed the most significant changes in both optical properties and OP, indicating its highest sensitivity to visible light aging. Molecular composition analysis revealed that the reduction of polycyclic aromatic hydrocarbons (PAHs) and methyl-PAHs primarily affects the optical properties, while oxygenated PAHs play a major role in OP. Combined with the results from reactive oxygen species detection, it is suggested that EC initiates photoreactions by generating superoxide anions, while OC undergoes compositional changes that result in subsequent atmospheric effects. These findings enhance our understanding of the photochemical aging process of soot particles and their implications for climate and health.

Controllable generation of engine exhaust similar soot particles using an inverted nitrogen-diluted flame burner for calibration purpose

The calibration of vehicle engine exhaust PN analyzers has been a challenge due to the significant difference in properties between calibration particles and measured particles. In this study, an inverted nitrogen-diluted flame burner was designed to generate engine exhaust similar soot particles and evaluated for calibration use. The burner can produce reference-unimodal soot particles at 61–311 nm and total number concentration up to 108 #/cm3 by adjusting the flow rate of ethylene, nitrogen and air. Excellent stability of 0.91 % enables it to generate a fairly stable calibration particle flow. Mixing nitrogen in ethylene makes burner have a high degree of variability in generating smaller particles. The properties of size distribution, morphology, effective density indicate that the generated soot particles can simulate well with engine exhaust particles. TOA results indicate that the soot have high TC mass concentration of over 559.26 mg/m3 and EC/TC fraction of over 90 %.

Investigating the formation of soot in CH4 pyrolysis reactor: A numerical, experimental, and characterization study

Methane pyrolysis is a promising method for eco-friendly hydrogen production, but soot formation and carbon interaction pose challenges for scaling up. Therefore, understanding the dynamics of soot formation and carbon deposition is crucial. This study delves into the intricacies of soot formation in methane pyrolysis under industrially relevant conditions, namely operations at atmospheric pressure, employing a H2:CH4 ratio of 2 and exploring a range of hot zone temperatures (1473 K, 1573 K, 1673 K, and 1773 K) with a 5 s residence time. Utilizing a detailed gas-phase kinetic model with direct carbon deposition reactions, the research adopts the method of moments coupled with a one-dimensional plug flow reactor model to simulate soot formation. The model is validated by characterizing soot particles that were produced in a pyrolysis reactor by means of transmission electron microscopy, Dynamic light scattering (DLS), and Raman spectroscopy. Results show that lower temperatures lead to nucleation-dominated growth, whereas higher temperatures significantly restrain particle growth due to carbon deposition. DLS data indicate a complex balance between particle growth and deposition processes. These findings provide insights into operational parameters that can enhance reactor performance and sustainability in hydrogen production processes by mitigating soot and carbon deposition.

Retraction: Effects of thermal aging atmospheres on oxidation activity, element composition and microstructure of diesel soot particles.

[This retracts the article DOI: 10.1039/D3RA05340G.].

Impact of meteorological parameters on black carbon mass concentrations over Silicon City “ Bengaluru, Southern part of India” – A Case Study

In the context of Bengaluru, the impact of black carbon (BC) aerosols on regional climate dynamics emerges as a crucial area of investigation. Due to the lack of high-resolution BC data, it was collected at 5 different locations in Bengaluru, Karnataka, from January 2019 to December 2019. The mean mass concentration of BC was 5.91 microg m-3, whereas the higher mass concentration of BC was 7.71 microg m-3 over the city railway station and the lower (3.69 microg m-3) was in Jayanagara. The contribution of BC in higher-traffic and industrial locations was approximately 41% higher than the residential locations, which indicates a large fraction of soot particles are from anthropogenic activities mainly from fossil fuel combustion. The seasonal concentrations of BC have also exhibited a large variability, with the highest sequence in magnitude during the winter season (9 microg m-3) followed by the summer (6.3 microg m-3), post-monsoon (5.8 microg m-3) and monsoon (3.4 microg m-3) seasons during the study period. The concentrations of BC during the monsoon season were very low as compared to the winter season due to the impact of the washout effect. The BC was negatively significantly correlated (-0.70) with rainfall indicating the washout effect, however, during the winter season, it was due to impact of boundary layer condition. Overall (annually) the mean concentrations of BC have increased by around 55% within five years over the urban region, which indicates the impact of man-made activities. The higher mass concentration of BC over Bangalore in the southern part of India, indicates serious implications for the regional climate that need to be investigated and mitigated. Finally, the study suggests that immediate action is required to mitigate the emission of BC into the urban environment in the southern part of India.

Oxygen-Free Reforming of Methane into Synthesis Gas in the Presence of H2, H2O, CO, and CO2 Additives Taking into Account the Formation of Soot Particles

Oxygen-Free Reforming of Methane into Synthesis Gas in the Presence of H2, H2O, CO, and CO2 Additives Taking into Account the Formation of Soot Particles

Oxidation of Polycyclic Aromatic Hydrocarbons (PAHs) Triggered by a Photochemical Synergistic Effect between High- and Low-Molecular-Weight PAHs.

Photooxidation of polycyclic aromatic hydrocarbons (PAHs), which are widely observed in atmospheric particulate matter (PM), largely determines their atmospheric fate. In the environment, PAHs are highly complex in chemical composition, and a great variety of PAHs tend to co-occur. Despite extensive investigation on the photochemical behavior of individual PAH molecules, the photochemical interaction among these coexisting PAHs is still not well understood. Here, we show that during photooxidation, there is a strong photochemical synergistic effect among PAHs extracted from soot particles. We find that neither small PAHs with low molecular weights of 200-350 Da and 4-8 aromatic rings (named PAHsmall) nor large PAHs with high molecular weights of 350-600 Da and 8-14 aromatic rings (named PAHlarge) undergo photooxidation under red-light irradiation (λ = 648 nm), even though PAHlarge can absorb light with this wavelength. Interestingly, when PAHlarge is mixed with PAHsmall, substantial photooxidation is observed for both PAHlarge and PAHsmall. Comparisons of in situ infrared (IR), high-resolution mass spectrometry, and electron paramagnetic resonance analysis indicate that the presence of PAHsmall inhibits the light quenching effect arising from the π-π stacking of PAHlarge. This leads to the formation of singlet oxygen (1O2), which initiates the photooxidation. Our findings reveal a new mechanism for the photooxidation of PAHs and suggest that complex atmospheric PAHs exhibit distinct photoreactivity from simple systems.

Novel and active Bi2Zr1.9M0.1O7 (M = Mn, Fe, Co, Ni) catalysts for soot particle removal: Engineering surface with rich oxygen defects via partial substitution of Zr‐site

Novel and active Bi₂Zr_1.9M_0.1O₇ (M = Mn, Fe, Co, Ni) catalysts for soot particle removal: Engineering surface with rich oxygen defects via partial substitution of Zr‐site

Revisiting Contrail Ice Formation: Impact of Primary Soot Particle Sizes and Contribution of Volatile Particles.

Aircraft contrails, formed largely on soot particles in current flights, are important for aviation's non-CO2 climate impact. Here we show that the activation of nonvolatile soot particles during contrail formation is likely determined by the sizes of primary soot particles rather than the effective sizes of soot aggregates as assumed in previous studies, which can explain less-than-unity fractions of soot particles forming contrail ice particles as recently observed during ECLIF (Emission and CLimate Impact of alternative Fuels) campaigns. The smaller soot primary sizes compared to aggregate sizes delay the onset of contrail ice formation, increase the maximum plume supersaturation reached in the contrail plume, and thus increase the probability of small volatile particles contributing to the total contrail ice particle number. This study suggests that the range of conditions for volatile plume particles to contribute significantly to the contrail ice number budget is wider than previously thought. As the aviation industry is moving toward sustainable aviation fuel and/or lean-burning engine technology, which is expected to reduce not only the emission index of nonvolatile soot particles but also the sizes of primary soot particles, this study highlights the need to better understand how the combined changes may affect contrail formation, contribution of volatile particles, and climate impacts.

Plasma treatment on flame soot: view from nanostructure and reactivity of soot

In recent years, the use of plasma for pollutant emission control has an expected potential. In this study, soot particles from flames were sampled from an ethylene inverse diffusion flame, which were placed in a self-designed dielectric barrier discharge plasma device for reaction treatment. The nanostructure and oxidation reactivity of soot particles after plasma treatment were evaluated by transmission electron microscopy, Raman spectroscopy, X-ray diffraction analysis and X-ray photoelectron spectroscopy. With 16 kV, 2.5 kHz as an example, with the treatment of plasma, the fringe length decreases (1.3% and 9.6%), and the fringe tortuosity increases (1.1% and 8.7%) in both high-maturity and low-maturity soot particles, which means that the oxidation activity of soot is enhanced after plasma discharge. Raman spectra, X-ray diffraction analysis spectra and X-ray photoelectron spectroscopy spectra have confirmed this phenomenon, especially the oxidation activity of soot particles under the action of plasma at high maturity is more obvious. It is worth noting that the enhancement of soot oxidation activity after plasma discharge has certain limitations, that is, the oxidation activity will not continue to increase after it is enhanced to a certain intensity, which may be related to the selection of Ar as the atmosphere gas.

Analysis of the nanostructure evolution of soot in n-heptane/iso-octane with 2,5-dimethylfuran addition: A combined experimental study and ReaxFF MD simulations

The soot formation of n-heptane/iso-octane doped 2,5-dimethylfuran (DMF) with different ratios was experimentally investigated through laminar diffusion flame and numerically simulated by using the pyrolysis simulations method of reactive force field molecular dynamics (ReaxFF MD). The results showed that the laminar diffusion flame height of n-heptane/iso-octane increased with increasing DMF doping ratio. At a consistent sampling height, the primary soot particle sampling numbers collected were first decreasing and then increasing, and the size of the primary soot particle was first increasing and then decreasing accompanied by the DMF doping ratio increasing. Furthermore, the transmission electron microscope (TEM) analysis provided that DMF initially inhibited and subsequently promoted the primary soot particle growth in the n-heptane/iso-octane flame. The core-shell ratio increased and then decreased with the increase of the DMF doping ratio, which indicated that the maturity of soot decreased and then increased. In n-heptane/iso-octane doped with DMF ReaxFF MD pyrolysis simulation, it was divided into three stages 0–0.5 ns (the first stage), 0.5–3 ns (the second stage), and 3–4.5 ns (the third stage). Fuel decomposed in the first stage and reacted violently in the second stage. The soot precursors continued to react, molecule size kept to increase, and the polycyclic aromatic hydrocarbons (PAHs) continued to grow. In the third stage, the carbon number of the largest molecules were slowly increasing, and the development of soot entered mature stage, where the H/C ratio was slowly decreasing. Through ReaxFF MD simulations, it was found that the maturity of soot exhibited decreasing and then increasing trend with the increase of DMF doping ratio. The graphene-like structures were mainly concentrated around the H/C ratio of 0.297 region.

Lubrication antagonism mechanism of nano-MoS2 and soot particles in ester base oil

Spherical nano-MoS2 (S-MoS2) has excellent lubricating properties and potential application value in engine oil additives. Engine soot can enter the engine oil, so the tribological interaction between S-MoS2 and diesel combustion soot (DCS) should be investigated. In this study, DCS was used to simulate engine soot. The interaction was investigated in dioctyl sebacate (DOS), and the interaction mechanism was full characterized. Results showed that S-MoS2 and DCS had obvious antagonism effects on lubrication. The 0.5% S-MoS2 exhibited good lubricating properties in DOS, which could reduce friction by ∼22% and wear by ∼54%. However, after 0.5% S-MoS2 was added to the 0.5% DCS contaminated DOS, the lubrication performance was not improved and was even worse than that without S-MoS2. When S-MoS2 was added for DOS lubrication, a tribofilm containing MoS2 formed on the friction surface, but simultaneously adding 0.5% DCS resulted in the disappearance of the MoS2 tribofilm. Moreover, under the action of friction heat, DCS and S-MoS2 could form hard MoxCy, thereby increasing abrasive wear. Finally, a preliminary deantagonism method was provided. After 2.0% zinc isooctyl dithiophosphate was added to the above antagonistic system, the friction coefficient did not show visible changes, but the wear recovered to a level close to that when only S-MoS2 was added. The antiantagonism method is not very satisfactory and some more efficient methods need to be further explored.

The chemical composition of secondary organic aerosols regulates transcriptomic and metabolomic signaling in an epithelial-endothelial in vitro coculture

BackgroundThe formation of secondary organic aerosols (SOA) by atmospheric oxidation reactions substantially contributes to the burden of fine particulate matter (PM2.5), which has been associated with adverse health effects (e.g., cardiovascular diseases). However, the molecular and cellular effects of atmospheric aging on aerosol toxicity have not been fully elucidated, especially in model systems that enable cell-to-cell signaling.MethodsIn this study, we aimed to elucidate the complexity of atmospheric aerosol toxicology by exposing a coculture model system consisting of an alveolar (A549) and an endothelial (EA.hy926) cell line seeded in a 3D orientation at the air‒liquid interface for 4 h to model aerosols. Simulation of atmospheric aging was performed on volatile biogenic (β-pinene) or anthropogenic (naphthalene) precursors of SOA condensing on soot particles. The similar physical properties for both SOA, but distinct differences in chemical composition (e.g., aromatic compounds, oxidation state, unsaturated carbonyls) enabled to determine specifically induced toxic effects of SOA.ResultsIn A549 cells, exposure to naphthalene-derived SOA induced stress-related airway remodeling and an early type I immune response to a greater extent. Transcriptomic analysis of EA.hy926 cells not directly exposed to aerosol and integration with metabolome data indicated generalized systemic effects resulting from the activation of early response genes and the involvement of cardiovascular disease (CVD) -related pathways, such as the intracellular signal transduction pathway (PI3K/AKT) and pathways associated with endothelial dysfunction (iNOS; PDGF). Greater induction following anthropogenic SOA exposure might be causative for the observed secondary genotoxicity.ConclusionOur findings revealed that the specific effects of SOA on directly exposed epithelial cells are highly dependent on the chemical identity, whereas non directly exposed endothelial cells exhibit more generalized systemic effects with the activation of early stress response genes and the involvement of CVD-related pathways. However, a greater correlation was made between the exposure to the anthropogenic SOA compared to the biogenic SOA. In summary, our study highlights the importance of chemical aerosol composition and the use of cell systems with cell-to-cell interplay on toxicological outcomes.Graphical