Primary Soot Particles Research Articles

From molecular to sub-μm scale: The interplay of precursor concentrations, primary particle size, and carbon nanostructure during soot formation in counter-flow diffusion flames

The focus of this work is on counter-flow diffusion flames of C2H4/air near the sooting limit (fV < 500 ppb) to shed light on the transition of precursor molecules to primary soot particles and their nanostructure. The applied experimental techniques cover non-intrusive methods based on laser-induced incandescence (LII) for determination of soot volume fractions, primary particle sizes, and ratios of refractive indices for absorption at different wavelengths. The methods are complemented by intrusive methods such as sampling with microprobes and analysis of gas composition by gas chromatography and mass spectrometry, particle sizing by differential mobility analysis, and determining carbon nanostructures of particles by high-resolution transmission electron microscopy (HRTEM). For numerical simulation, the well-known ABF-model is applied.The experimentally determined structures of the counter-flow flames could be well reproduced within the experimental uncertainties by the ABF-model for varying fuel mass fractions and strain rates. The numerical simulations identify the different processes during particle formation and the main variation can be attributed to variation of surface growth rates when applying strain rates and fuel mass fractions leading to higher soot volume fractions. Particle size distributions detected in the fuel flow near and below the stagnation plane appear bimodal with distinct maxima at particles sizes about 5 nm and 20 nm. The nanostructure of the primary particles exhibits basic structural units (BSUs), that increase up to the size of 7 Å to 10 Å at increasing soot volume fractions from about 100 ppb to 300 ppb. This coincides with the increase of the mole fractions of the detectable soot precursors with increasing soot volume fraction. The ratios of refractive index functions for absorption E(m,λ532)/E(m,λ1064) and E(m,λ266)/E(m,λ1064) decrease approximately linearly with increasing soot volume fractions. This is corroborated by the analyses of HRTEM-images that clearly bring about increasing sized BSUs with increasing soot volume fractions causing a shift of the absorption to larger wavelengths.

Dynamics of soot surface growth and agglomeration by enclosed spray combustion of jet fuel

Understanding the dynamics of soot formation and growth during combustion of jet fuel is essential for mitigation of aircraft engine emissions. Here, soot formation during enclosed spray combustion of jet fuel is investigated for its capacity to form soot with comparable characteristics to that from aircraft engines. For this, microscopy, scanning mobility particle, X-ray diffraction & Raman spectroscopy measurements and discrete element modeling (DEM) are employed along the flame centerline at various Effective eQuivalence Ratios (EQR). The DEM-derived mobility and primary particle size distribution dynamics are in excellent agreement with those measured at 5–63 cm height above the burner (HAB) for the measured temperature and soot volume fraction. At low EQR (1.46 and 1.59), soot surface growth stops at residence time, t = 4–7 ms, resulting in median soot primary particle diameters, d¯p, of ∼ 14 nm. At longer t (high HAB), agglomeration takes over increasing the median mobility diameter from 16 to 88 or 145 nm at EQR of 1.46 or 1.59, respectively, without altering d¯p and having the disorder over graphitic Raman band ratio, D/G = 0.9 ± 0.01 and a crystallite length, Lc = 1.24 ± 0.02 nm. In contrast, increasing EQR from 1.59 to 1.88, enhances soot surface growth, increases d¯p up to 23 nm and results in more graphitic soot having D/G = 0.8 ± 0.01 and Lc = 1.47 ± 0.01 nm. Furthermore, the D/G of soot is inversely proportional to its d¯p that is determined largely by surface growth.

Effects of ammonia on morphological characteristics and nanostructure of soot in the combustion of diesel surrogate fuels

The morphological characteristics and nanostructure of soot particles in pure n-heptane (C7H16) and n-heptane/ammonia co-flow diffusion flames were analyzed and compared using thermophoretic sampling and transmission electron microscopy (TEM) observation combining with quantitative image information extraction methods. The results showed that the overall formation and evolution of soot particles in NH3-doped n-heptane flames along the flame centerline were similar with that without NH3-doping. However, compared to n-heptane flame, the peak average diameter of primary soot particles and the peak gyration radius of soot aggregates in NH3-doped flames were reduced by about 45% and 37%, respectively, which indicated that the growth of both primary soot particles via surface reaction/condensation and soot aggregates via coagulation were significantly decreased. Meanwhile, the fractal dimension of soot aggregates was lower with NH3 addition as the structure of soot aggregates was looser and tended to be more chain-like. After NH3 doping, the peak average fringe length inside soot particles was decreased by 13%, and the inter-fringe spacing and tortuosity of soot were increased by 8% and 3%, respectively. This represented a more disordered microcrystal structure and lower degree of graphitization of soot particles, meaningfully indicating a higher oxidation reactivity.

Soot growth mechanism in C2H2 combustion with H2 addition: A reactive molecular dynamics study

A numerical investigation of the effect of H2 addition on soot formation was conducted in C2H2 combustion process from the molecular level. The results showed that the chemical effect of H2 (CE-H2) inhibited the soot formation of C2H2 combustion. With the gradual increase of H2 doping ratio, the soot morphology became sparser and the soot particle size decreased. The CE-H2 significantly inhibited the surface growth and coalescence of soot. Addition of H2 led to an increase in the H2 concentration in the combustion process, which inhibited the dehydrogenation reaction of the primary soot particle with C2H2, free radicals, and polycyclic aromatic hydrocarbons (PAHs). The CE-H2 increased the consumption rate of C2H2 and the formation rate of H2O, and it decreased the formation rate of CO. Moreover, the addition reaction of free radicals and PAHs played an important role in the soot growth process, which effectively promoted the soot surface growth process. And the coalescence process significantly increased the soot mass and affected the soot size and morphology although its frequency was relatively low.

Influence of an iron compound added to coal on soot formation

Soot formation is one major challenge in developing clean and efficient utilizes based on hydrocarbon fuels. We report the physical and chemical characteristics of a set of soot samples obtained from coal and coal mixed with iron nitrate pyrolysis on a drop tube furnace at different reaction times. Yimin lignite was chosen for the experiments, using acid washing to remove its metals and adding iron by impregnation. The pyrolysis processes of the two coal samples were analyzed by TG-DTG, DSC and MS. Characterization was carried out with transmission electron microscopy(TEM), Raman spectrometer, X-ray photoelectron spectroscopy(XPS), and infrared spectroscopy (FTIR). The results show that the iron nitrate significantly reduces the yield of soot and decreases the sizes of the primary soot particles. This inhibition effect on soot production increase with reaction time. With the addition of iron nitrate, the carbon lamellae in soot are more graphitized, but the primary particle surface roughness increases. In addition, the addition of iron results in more aliphatic functional groups and C–O on the surface of the soot.

Effects of blending methane, propane, and propylene on soot evolution in ethylene diffusion flames based on optical diagnostics

Soot evolution of the ethylene-based laminar coflow diffusion flame doping with methane, propane, and propylene with the blending ratio ranging from 0 to 50% has been investigated experimentally. These fuels were selected for their different fuel structure. Spatially resolved distribution maps of the flame temperature, soot volume fraction, the fluorescence signals of polycyclic aromatic hydrocarbons (PAHs), and primary soot particle diameter and number density were determined utilizing laser-induced incandescence (LII), laser-induced fluorescence (LIF), and ratio pyrometry (RP). It was found that the flame height surged and the flame temperature dropped dramatically when the propylene blending ratio was 20% while they were almost constant with the increasing addition of methane or propane. The soot/PAHs loading decreased monotonically with the addition of methane and the opposite was true in the cases of blending propylene. The synergistic effect of mixing propane into ethylene was found on both the soot/PAHs loading. The same trends were observed in the percentage of carbon conversion to soot and the primary soot particle diameter. It can be seen from the soot evolution analysis that methane addition suppressed the soot nucleation and surface growth simultaneously. The enhanced soot surface growth for the flames doping with propane at a low addition level and for the whole flame sets doping with propylene were attributed to the earlier inception time and the longer mass growth time. The preferential diffusion and weakened oxidation of soot particles because of the decreased flame temperature perhaps accounted for the transition from a non-smoking flame to a smoking flame when the propylene blending ratio was greater than 40%.

Impact of alcohol–diesel fuel blends on soot primary particle size in a compression ignition engine

The use of alternative fuels, such as bio-alcohols, in advanced propulsion systems could a feasible strategy to address several of the current issues associated to the use of internal combustion engines fuelled by carbonaceous fossil fuels. Particularly, soot particles, are one of the key pollutants emitted from compression ignition engines. Therefore, the development of soot formation prediction models providing new understanding on the impact of alternative fuels combustion in compression ignition engines become essential for soot mitigation purposes.This study proposes a new semi-empirical model that predicts in-cylinder soot primary particle growth from an engine fuelled with alcohol–diesel fuel blends. The model uses macroscopic experimental measurements of engine parameters such as instantaneous in-cylinder pressure. Furthermore, an empirical correlation is presented predicting the mean soot primary particle size as a function of alcohol–diesel fuel blend properties and fuel/air ratio. The experimental measurement of primary soot particle mean size are obtained from High Resolution Transmission Electron Microscope (HT-TEM) micrographs obtained from soot particles collected via thermophoresis. Overall, the research findings presented in this work contributes to propose environmentally friendly fuel candidates for transportation.

Time-resolved 2D angular scattering of soot particles in atmospheric turbulent flames

A better understanding of the formation of soot particles is essential to improve combustion-related processes. For this purpose, this work reports for the first time the measurement of the size of soot particles under formation in a turbulent atmospheric flame in a planar configuration. This is ensured by the detection of the elastic scattering of a laser sheet thanks to two cameras positioned at different scattering angles (45° and 135°). The size information is then used to interpret the scattering signal collected by an additional camera positioned at 90° in order to evaluate the soot number concentration. This last step relies on a calibration ensured by soot volume fraction and primary particle size previously determined by autocompensating laser-induced incandescence in the same flame. Moreover, the use of a 1 kHz repetition rate nanosecond laser and three high speed CMOS cameras enables the access to these physical parameters with a high temporal resolution. The 2D and time-resolved soot characterization is of interest because it enables the observation of the temporal and spatial modifications of soot structures when propagating in such turbulent flames. In particular, in this flame, the transport and mixing of soot pockets are clearly observed and the impact of these processes on the size and number concentration is quantified.

Soot volume fraction and size measurements over laminar pool flames and pre-vaporised non-premixed flames of biofuels, methyl esters and blends with diesel

Previous studies have demonstrated that methyl ester-based biodiesels produce significantly less soot compared to petroleum diesel in standard diffusion flames. However, the roles of the oxygen content and the degrees of unsaturation (DoU) of the biodiesels on their sooting propensity have not been independently analysed. In the present study, the relationship between soot yield of biodiesels and the DoU of the fuel is systematically analysed in laminar pool flames and pre-vaporised diffusion flames. The spatial distribution of soot volume fraction of the flames fuelled with four biodiesel fuels, two methyl esters and their blends with diesel are quantitatively measured using laser induced incandescence. All six biofuels have different DoU but similar oxygen mass fractions, so that the effect of the DoU on soot formation could be separately considered. The soot yield using biodiesels was measured to be lower than that of diesel fuel by a factor up to 7.5 in pool flames and by a factor of 4.0 in vapour flames. In both flame setups, the soot reduction effect of biodiesels ranks in order of DoU. The more saturated the fuel molecule is, the lower the soot yield. The soot reduction effect of the blending ratio with biodiesel was found to be non-linear, and different in pool and vapour flames. The morphology, size, and number density of soot particles were analysed using scanning electronic microscopy. The results suggest that the shape of primary soot particles is close to spherical and the structure of the point-contact aggregates is similar in all cases. Biofuels not only produce smaller particle sizes, but also fewer particles compared to diesel. Chemical kinetic simulations suggest that blending of biodiesels reduces the soot yield primarily by slowing the soot surface growth process, and secondarily by prohibiting the soot nucleation and inception. Both the nucleation (C3H3 and benzene) and growth species (C2H2) for soot formation take place more quickly and intensely for the combustion of more unsaturated fuels, which results in the correspondingly larger soot yield.

Effects of ammonia addition on soot formation in ethylene laminar diffusion flames. Part 3. The morphology and nanostructure of soot particles

Ammonia (NH3) fuel has been widely considered a competitive alternative fuel and hydrogen carrier due to its “non-carbon and hydrogen-rich” nature. In this study, the thermophoretic sampling combined with transmission electron microscopy (TEM) analysis was conducted to investigate the effects of NH3 addition with varying ratios (between 0% and 60% by volume fraction while the remainder is argon) on the evolution of morphology and nanostructures of soot particles along the flame axis in the ethylene (40% by volume fraction) co-flow diffusion flames. Results showed that the flame visible height increased with the addition of NH3, and the flame temperature decreased at the height above burner (HAB) below 30 mm while increased at HAB > 30 mm. With NH3 addition, the size of soot (primary particles and aggregates) and the number of soot primary particles contained in the soot aggregates decreased significantly. In addition, the investigation of soot nanostructures showed that the carbon layers with shorter fringe length (Fl) and higher tortuosity (Ft) would be oxidized before it arrived to the flame tip in the NH3-doped flame, resulting in the longer Fl and higher Ft. In general, the inter-fringe spacing (Fd) increased with NH3 addition. The evolution of soot morphology and nanostructures indicated that NH3 would delay the process of particle inception and surface growth.

Flamelet LES of a turbulent pulverized solid fuel flame using a detailed phenomenological soot model

In this work, large-eddy simulation (LES) is conducted for a turbulent pulverized coal flame with a detailed phenomenological model to characterize the soot evolution and a flamelet model to describe the detailed gas phase kinetics. In particular, a quadrature-based moment method (QBMM) is adopted to describe the soot statistics with the physicochemical processes of soot particle nucleation, condensation, coagulation, chemical surface growth and oxidization being considered. The simulation results are compared to the experimental data, including the direct photograph images, particle velocities, laser induced fluorescence (LIF) for polycyclic aromatic hydrocarbons (PAHs), laser induced incandescence (LII) for soot, scanning electron microscope (SEM) with the thermophoretic sampling (TS), and the time-resolved LII (TiRe-LII) for spatial soot particle size distribution. The comparisons show that the ignition position and the mean velocity of the coal particles can be accurately predicted with the proposed flamelet/QBMM/LES method, and an overall good agreement is also obtained when comparing against the PAHs-LIF, soot-LII and SEM images. The importance of the contributions of the different physicochemical processes to the soot particle volume growth is quantified by analyzing the corresponding moment source terms. It is found that for the pulverized coal flame studied, the chemical surface growth is the most important contribution to the soot volume growth at different locations along the streamwise direction. Although the nucleation does not make a significant contribution to soot volume growth, it determines the number density of the primary soot particles formed in the main flow region.

Hydrogen enrichment enhances soot formation in swirl-stabilized non-premixed turbulent combustion of ethylene in a model gas turbine combustor

A switch from fossil fuels to hydrogen is currently not feasible mostly due to supply and infrastructure issues. One of the possible approaches, and this is now practiced to a limited extent in industrial gas turbines, is to blend relatively small amounts of hydrogen with fossil fuels curbing the carbon dioxide emissions. However, studies assessing the influence of modest amounts of hydrogen blending with hydrocarbon fuels on soot processes yielded contradictory results. Most of these experimental and numerical studies were performed on laminar diffusion flames and studies on turbulent flames are scarce. One of the confounding factors in assessing the influence of hydrogen is selection of a control experiment in which the fossil fuel is blended with the same amount of an inert diluent. Using helium in the control experiment is preferable because of its similar transport properties and heat capacity to those of hydrogen. Hence, we studied the soot processes in a model gas turbine combustor in which the flame is stabilized by an air swirl. Swirl-stabilized platform ensures that with and without hydrogen/helium dilution, the hydrodynamics of the combustor stays fixed. Base fuel ethylene is supplemented with hydrogen or helium by the same amount to separate the dilution affects and assess the direct chemical interaction of hydrogen related to soot formation. Soot volume fraction and primary soot particle diameters were measured by auto-compensating laser induced-incandescence for all cases. Flow field data obtained using stereoscopic particle image velocimetry is utilized to ascertain the hydrodynamic effects on soot distribution due to addition of lighter species. Soot formation was found to be enhanced by the addition of hydrogen when allowance was made for the dilution effect using the helium doped flame experiments. Possible causes of this observation including the molecular diffusivities of hydrogen and helium, and chemical interaction are discussed.

Experimental effect of CuO2 nanoparticles into the RME and EGR rates on NOX and morphological characteristics of soot nanoparticles

In recent years, the adding nano additives to the fuel is paid much attention by decreasing the exhaust emissions and enhance combustion characteristics without any modifications in diesel engine. The effects of copper dioxide (CuO2) nanoparticles and exhaust gas recirculation (EGR) on combustion characteristics and morphological characteristics of soot nanoparticles in diesel engine fuelled with rapeseed methyl ester (RME) were investigated in this study. The good advantages of CuO2 nanoparticles such as good thermal properties, oxygen storage, and density thermophysical properties of viscosity are encourage to using as nano additives into the biodiesel. The results showed that the pressure inside cylinder and ROHR improved by 4% and 11%, respectively, from adding CuO2 nanoparticles into the RME in comparison neat RME. Furthermore, the BTE increased by 3.64%, 7.36%, 9.28% and 12.43% with adding CuO2 to the RME, while the BSFC decreased by 5.26%, 7.47%, 9.68% and 12.73% when adding nanoparticles to the RME under 25%, 50%, 75% and 100% of engine load, respectively, in comparison with diesel fuel. Adding CuO2 nanoparticles to the RME and 20% rate of EGR significantly decrease the NOX emissions by 29.64% when compared to the without nano additives. The number and concentration of soot nanoparticles were decreased with addition of CuO2 nanoparticles to the RME and they increased with presence EGR technology. It is indicated that the soot nanoparticles concentration decreased or was in par with neat RME when incorporation between EGR and nano additives. The morphological parameters such as number of soot primary particles (npo) exhibits significant reduction by 18%, meanwhile slightly increase in the average diameter of soot primary particles (dpo) by 7% with adding CuO2 to the RME for with and without EGR.

Simulation of the Formation and Growth of Soot Aerosol Particles in a Premixed Combustion Process Using a Soot Aerosol Dynamics Model

Recently, an aerosol dynamics model—the Soot Aggregate Moment Model (SAMM)—that can efficiently trace the size distribution and morphology of soot particles was developed. In order to examine the applicability of SAMM in association with open-source CFD and combustion chemistry solvers, the formation and growth of soot particles in a premixed ethylene/air combustion were simulated by connecting SAMM with OpenSMOKE++ in this study. The simulation results were compared with available measurements and with the results of a previous study conducted using SAMM connected with an in-house CFD code and the CHEMKIN combustion chemistry package. Both CHEMKIN and OpenSMOKE++ underestimated C2H2 concentration compared to previous measurements, with deviation from the measured data being smaller for OpenSMOKE++. The chemical mechanism adopted in the CHEMKIN package was found to underestimate pyrene concentration by a factor of several tens. OpenSMOKE++ predicted much higher soot precursor concentrations than CHEMKIN, leading to a higher nucleation rate and a faster surface growth in the latter part of the reactor. This resulted in a reasonable soot production rate without introducing an artificial condensation enhancement factor. The overestimation of low-molecular-weight polycyclic aromatic hydrocarbons in the latter part of the reactor and the neglect of sintering led to an overprediction of soot production and primary particle number. This result indicates that accounting only for obliteration without sintering in SAMM could not simulate the merging of primary particles sufficiently. This indication merits further investigation.

High-throughput generation of aircraft-like soot

High-throughput, laboratory units for generation of aircraft-like soot are needed to quantify and understand the impact of such emissions on public health and climate change due to the high costs and limited access to aircraft engines. Enclosed spray combustion of jet fuel is used here to generate high soot concentrations, up to 255 mg/m3, three orders of magnitude higher than those typically obtained by widely used soot generators that use vapor-fed flames. This is attributed mostly to the use of real jet fuels. The large mass concentrations enable routine characterization of the soot specific surface area (SSA) and pore size distribution (PSD) by N2 adsorption. The geometric mean mobility diameter, d¯m, of soot agglomerates was systematically varied from 15 to 180 nm by varying the equivalence ratio (EQR) at constant fuel feed rates, while the organic to total carbon (OC/TC) ratio is low (<20%) at all conditions. The geometric mean primary particle (PP) diameter, d¯p, standard deviation, σg,p, and mass-mobility exponent, Dfm, were hardly altered in that EQR range. These measured Dfm and σg,p indicate that soot PPs were sinter-bonded by surface growth, in agreement with aircraft emissions literature. Most importantly, soot made at EQR ≤ 1.34 has mainly small pores (<2 nm) and similar morphology (Dfm = 2.52 ± 0.17), SSA (160 − 239 m2/g), OC/TC (< 20%), d¯m (15 − 61 nm) and d¯p (14 nm) with those from high-thrust aircraft emissions.

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core–shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research.

The temperature dependence of soot formation in laminar coflow aromatic flames

The temperature sensitivity of n-propylbenzene and 1,2,4-trimethylbenzene on soot formation in coflow diffusion flames was assessed. Cases with air temperatures at 300K (LT), 473K (MT), and 673K (HT) were established. Soot volume fractions and primary particle diameters were measured by Laser-induced incandescence. Soot temperatures were measured by rapid thermocouple insertion with correction by backward extrapolation. Soot yield also increased with temperature. Compared to alkanes and alkenes, alkylbenzenes exhibited much lower temperature sensitivity. The model suggested that elevating the reactant temperature did not significantly affect the production of soot precursor PAH in alkylbenzene flames, but altered the buoyancy-induced acceleration, which subsequently determined the time available for soot growth. Soot formation was promoted by extending the available time. To isolate the impact of fuel temperature, a case with heated fuel and unheated air (FHT) was also assessed. It is found that raising the fuel temperature affected soot formation more along the centerline than on the wing. This is suggested to be related to the earlier soot inception for FHT along the centerline.

Effects of iron on coal pyrolysis-derived soot formation

Soot formation is one major challenge in developing clean and efficient utilizes based on hydrocarbon fuels. In this work, ferric nitrate was selected as an iron additive to be loaded into pulverized coal, and the pyrolysis experiment with an inert atmosphere was conducted in a high-temperature drop tube furnace (DTF). The physical and chemical character of the soot obtained from coal samples with different iron content were analyzed to explore the effect of the soot format process. The results showed that the soot yield was reduced 7% and 23%, respectively, at the same conditions when the content of iron in the coal sample was 0.51% and 0.87%. After iron was added, the diameter of soot primary particles was reduced from 50.8 nm to 37.4 and 37.8 nm, and the Df of soot aggregates increased, indicating that iron inhibited the growth process of soot primary particles and promoted the agglomeration between particles. Thus, the degree of graphitization of soot increased. In addition, the content of C–O functional groups in soot derived from coal with iron addition increased significantly, which implied that the participation of iron enhanced the oxidation reaction of soot.

Effect of Atmospheric Aging on Soot Particle Toxicity in Lung Cell Models at the Air-Liquid Interface: Differential Toxicological Impacts of Biogenic and Anthropogenic Secondary Organic Aerosols (SOAs).

Background:Secondary organic aerosols (SOAs) formed from anthropogenic or biogenic gaseous precursors in the atmosphere substantially contribute to the ambient fine particulate matter [PM in aerodynamic diameter ()] burden, which has been associated with adverse human health effects. However, there is only limited evidence on their differential toxicological impact.Objectives:We aimed to discriminate toxicological effects of aerosols generated by atmospheric aging on combustion soot particles (SPs) of gaseous biogenic () or anthropogenic (naphthalene) precursors in two different lung cell models exposed at the air–liquid interface (ALI).Methods:Mono- or cocultures of lung epithelial cells (A549) and endothelial cells (EA.hy926) were exposed at the ALI for 4 h to different aerosol concentrations of a photochemically aged mixture of primary combustion SP and () or naphthalene (). The internally mixed soot/SOA particles were comprehensively characterized in terms of their physical and chemical properties. We conducted toxicity tests to determine cytotoxicity, intracellular oxidative stress, primary and secondary genotoxicity, as well as inflammatory and angiogenic effects.Results:We observed considerable toxicity-related outcomes in cells treated with either SOA type. Greater adverse effects were measured for compared with in both cell models, whereas the nano-sized soot cores alone showed only minor effects. At the functional level, we found that augmented the secretion of malondialdehyde and interleukin-8 and may have induced the activation of endothelial cells in the coculture system. This activation was confirmed by comet assay, suggesting secondary genotoxicity and greater angiogenic potential. Chemical characterization of PM revealed distinct qualitative differences in the composition of the two secondary aerosol types.Discussion:In this study using A549 and EA.hy926 cells exposed at ALI, SOA compounds had greater toxicity than primary SPs. Photochemical aging of naphthalene was associated with the formation of more oxidized, more aromatic SOAs with a higher oxidative potential and toxicity compared with . Thus, we conclude that the influence of atmospheric chemistry on the chemical PM composition plays a crucial role for the adverse health outcome of emissions. https://doi.org/10.1289/EHP9413

Effect of ion-exchangeable calcium on carbonaceous particulate matter formation during coal pyrolysis

This work investigated the effect of ion-exchangeable calcium on the mass yield, size distribution and structural properties of carbonaceous particulate matter from coal pyrolysis. The raw, acid washed and calcium-exchanged coal samples were pyrolyzed in a flat-flame burner at 1600 K. The particulate matter was collected with a three-stage dilution sampler. Then, the particle size distributions were measured by a low pressure impactor (DLPI+) and a scan mobility particle sizer (SMPS). The results show that, with the addition of ion-exchangeable calcium, the soot yield reduces, and the size growth of soot particles is inhibited. Transmission electron microscopy (TEM) analysis shows that ion-exchangeable calcium diminishes the sizes of disordered cores in soot primary particles, accelerates the graphitization of soot and makes the soot aggregates more compact. The chemical structures derived from Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) indicate that the graphitization degree of the soot is first enhanced and then inhibited with increasing calcium loading amount. Additionally, the inorganic species in the size-segregated soot particles were characterized. The fractions of calcium and sodium in soot show opposite trend with particle size. Unlike Na, which nucleates before soot inception, Ca tends to participate in both the soot nucleation and surface growth processes, and is enriched at larger particle size.