Composition Of Soot Research Articles

Photocatalytic performance of Soot/TiO2 nanocomposite against toxic dye

Nowadays, composing semiconductors with carbon structures to enhance their optical properties shows huge interest as a nanophotocatalyst for trending applications (i.e., photodegrading pollutants). In this study, TiO2 and soot/TiO2 nanocomposites were prepared via a one-step sol-gel assisted hydrothermal method, using a temperature of 220 °C and a reaction time of 6 h. Characterization by X-ray diffraction and Raman spectroscopy confirmed that the resulting TiO2 and soot/TiO2 materials exhibited a pure anatase crystal phase, without the presence of other TiO2 polymorphs. Soot composition on TiO2 showed enhanced photocatalysis properties, such as a lower combination rate of electron-hole pairs than pure TiO2. Crystal violet (CV) was applied as a pollutant model to examine the photocatalytic degradation of synthesized TiO2 and soot/TiO2. The photodegradation experiments of CV dye in its aqueous media by UV light interaction showed 26.63 % and 89.09 % in the presence of TiO2 and soot/TiO2 nanocomposite, respectively. In the basic media (pH 11), maximum photodegradation (97.95 %) is attained when 0.004 g of Photocatalyst (soot/TiO2) is used. Using the recycled photocatalyst, the dye's photodegradation efficiency remained high throughout the reusability cycles, even after four consecutive cycles.

Evaluating the efficacy of targeted traffic management interventions: A novel methodology for determining the composition of particulate matter in urban air pollution hotspots

Worldwide, there is an increasing uptake of traffic management interventions aimed at reducing the impact of traffic related air pollution on public health. However, the evidence base linking the proposed changes with the resulting improvements in air quality is lacking. In this paper we present data from a micro-network of low-cost PM10 samplers collected from an isolated urban centre (Auckland, New Zealand). The data was then analysed using a new combination of analytical methods aimed to identify the composition and hence, the source of pollution. Whilst across the three sites mass concentration of PM10 and black carbon were similar, Raman spectroscopy successfully identified variations in the soot composition at different sites, enabling some particulate matter to be linked to diesel vehicle emissions. A mass reconstruction approach proved useful in determining that the airshed is well-mixed and also highlighted the impacts of urban design on recorded concentrations. The results show that networks of low-cost sensors, combined with the range of analytical techniques used here can help policymakers test the efficacy of interventions and management strategies designed to combat the burden of air pollution on public health.

Formation mechanism of environmentally persistent free radicals during soot aging

Environmentally persistent free radicals (EPFRs) are a newly emerging class of pollutants that are known to be formed on metal oxides (MOs). Recent experimental investigations have suggested that EPFRs may also be formed on soot. However, little is known about the structural and compositional characteristics of soot surfaces conducive to EPFRs formation. Concurrently, the changes in the surface structure and composition of soot indicate its aging process, yet the detailed mechanism underlying EPFRs formation in this process remain obscure. Additionally, it is uncertain whether the formation mechanism of EPFRs on soot differs from that on MOs. In this study, the density functional theory (DFT) and ab initio molecular dynamics (AIMD) were used to investigate EPFRs formation on soot at different stages of aging. The results indicate that EPFRs could be formed on both the complete soot surface with hydroxyl groups and the defective surface. Correspondingly, during the aging process of soot, the formation trend of EPFRs increases in the early stage of the aging process and then decreases over time. Additionally, the formation mechanism on soot is different from that on CuO. On soot, the EPFRs formation is initiated by free hydroxyl radical formed through the desorption process, following the Eley-Rideal mechanism, while on CuO surfaces, its formation involves the surface-bound hydroxyl groups, and thus follows the Langmuir-Hinshelwood mechanism. Furthermore, EPFRs triggered by soot are less stable than those by CuO, due to the easier desorption process of phenoxyl radicals on soot. These findings provide valuable insights into the detailed formation mechanism of EPFRs on soot at different stages of aging, thereby contributing to control EPFRs emissions from a mechanism perspective.

Particle Number Concentration and SEM-EDX Analyses of an Auxiliary Heating Device in Operation with Different Fossil and Renewable Fuel

Pollution from road vehicles enters the air environment from many sources. One such source could be if the vehicle is equipped with an auxiliary heater. They can be classified according to whether they work with diesel or gasoline and whether they heat water or air. The subject of our research series is an additional heating system that heats the air, the original fuel is gasoline. This device has been built up in a modern engine test bench, where the environmental parameters can be controlled. The length of the test cycle was chosen to be 30 min. The tested fuels were E10, E30, E100 and B7. A 30-min operating period has been chosen in the NORMAL operating mode of the device as a test cycle. The focus of the tests was particle number concentration and soot composition. The results of the particle number concentration showed that renewable fuel content significantly reduces the number concentration of the emitted particles (9.56 × 108 #/cycle for E10 vs. 1.65 × 108 #/cycle for E100), while B7 causes a significantly higher number of emissions than E10 (3.92 × 1010 #/cycle for B7). Based on the elemental analysis, most deposits are elemental carbon, but non-organic compounds are also present. Carbon (92.18 m/m% for E10), oxygen (6.34 m/m% for E10), fluorine (0.64 m/m% for E10), and zinc (0.56 m/m% for E10) have been found in the largest quantity of deposits taken form the combustion chamber.

Functionalization of fullerene soot through oxidative decarboxylative coupling with silver dinitrobenzoate

In this research, we extend the functionalization of fullerene soot with nitroaryl substituents through oxidative decarboxylative coupling with silver 3,5-dinitrobenzoate. For this purpose, silver 3,5-dinitrobenzoate is first prepared in two-steps from 3,5-dinitrobenzoic acid. Then, this compound as a substrate together with potassium persulfate as an oxidant is used in acetonitrile as a solvent to functionalize fullerene soot. The reactions with different equivalent ratios of substrate and oxidant are conducted by both thermal and microwave conditions. This strategy is able to induce about 88.03 wt.% O and 5.79 wt.% N to the composition of fullerene soot. The advantage of this strategy is that the reaction can happen without the need for a catalyst, because silver(I) present in the substrate can catalyze the reaction progress. To prove the functionalization, several characterization techniques are used, i.e. XRD patterns, EDX spectra and SEM elemental distribution images, FE-SEM and TEM micrographs, particle size distribution histograms, FT-IR and Raman spectra, as well as TGA and DSC curves, which demonstrate the changes on fullerene soot. The novelty of this research is that it provides a new strategy for oxidative decarboxylative coupling of silver(I) carboxylates with the carbon surface.

Composition and morphology of biomass-based soot from updraft gasifier system

Soot is an aerosol formed by incomplete combustion of carbonaceous materials, and its formation in biomass gasification is inevitable. It is crucial to know the properties of the soot produced in the exhaust of gasification reactors in order to appreciate both its advantages and disadvantages. In this study, a variety of analytical techniques were used to examine the content and morphology of biomass soot produced by a top-lit updraft gasifier. The results of the experiment revealed that carbon and oxygen make up the majority of the soot, with minor amounts of other components. Both aromatic and aliphatic groups with significant oxygen concentrations can be seen in the soot based on the distribution of functional groups. The morphology revealed an uneven, stratified, amorphous sample. Meanwhile, the sample had a surface area of 193.8 m2/g and a pore diameter of 2.68 nm. These porous qualities point to a potential use of the soot sample as an adsorbent in water filtration after activation.

Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Promotion of the NO-to-NO2 Conversion of a Biofueled Diesel Engine with Nonthermal Plasma-Assisted Low-Temperature Soot Incineration of a Diesel Particulate Filter

High-concentration biodiesel-diesel fuel blends are an alternative fuel widely used for compression ignition engines. However, commercial diesel engines are not designed and set up for high-concentration biodiesel-diesel fuel blends. Hence, the aim of this research was to investigate the nonthermal plasma (NTP) activities during an NOx reduction and the soot characteristics on an unmodified diesel engine (Euro V) that is fueled with various biodiesel blends with diesel under a low exhaust gas temperature (<250 °C). The experiment found that the soot composition of biodiesel fuel produces lower levels of soot when compared with diesel, in terms of both number and mass. In addition, the activation energies (Ea) of carbon oxidation under an oxygen atmosphere were found to be approximately 154.57–173.64 kJ/mol.

Soot biodegradation by psychrotolerant bacterial consortia.

To probe the bioavailability of soot released into the atmosphere is pivotal to understanding their environmental impacts. Soot aerosol absorbs organic matter, creating a hot spot for biogeochemical transformation and the global carbon cycle. Soot primarily contains condensed aromatics chemically recalcitrant; however, oligotrophic microorganisms might use it as a nutritional source. This study investigated the influence of psychrotolerant bacterial consortia on soot. Significant increase in the bacterial biomass, reduction in water-insoluble organic carbon (OC) and elemental carbon (EC) in soot residues and increase in water-soluble OC in the filtrate signifies the use of soot as a carbon and nutritional source. The influence on morphology and composition of soot was reported using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy, and Energy Dispersive X-Ray analysis (EDX). The FTIR analysis showed significant variations in the pattern of soot spectra, suggesting degradation. Elemental analysis and EDX showed a reduction in carbon percentage. Besides, the reduction of optical density with incubation time signifies the OC and EC consumption. This study shows that soot can be a substrate and pivotal factor in the microbial food web. Nowadays, soot emission to the environment is growing; therefore, soot involvement in microbe-mediated processes should be closely focused.

Emission of nanoparticles from coal and diesel fired power plants on Svalbard: An electron microscopy study

Sub-micrometer aerosol particles were collected at the stack of two coal power plants (Barentsburg, Longyearbyen), two diesel power plants (Pyramiden, Sveagruva) and one small-scale coal-burning boiler (Pyramiden) on the Arctic archipelago of Svalbard (Norway). Primary particles (n = 5752) in the size range of 100–1000 nm were investigated by operator-controlled high-resolution scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). Based on morphology and chemical composition primary particles were assigned to one of the following groups: soot, carbonaceous, fly ash spheres, Hg-containing particles, and mineral particles. Soot is the dominating particle group in most samples with a relative number abundance between 69 and 98%. Two coal burning samples have significantly lower soot contents of about 12 and 31%. The relative number abundance of the other particle groups is highly variable.The chemical composition of soot, fly ash spheres and mineral particles was studied in more detail. Soot particles from coal burning are significantly enriched in the elements S, Na, and K compared to diesel soot. The P contents of soot, fly ash spheres, and mineral particles reflect the variable concentration of this element in the different coal seams. Fly ash spheres from coal burning consist of a Si-rich component (quartz or silica glass), alumosilicates or alumosilicate glass, Fe oxides and a Fe, Ca, Al component (most likely a mechanical mixture of spinel and gypsum or lime). Fly ash spheres from diesel burning have a similar composition except that the Fe, Ca, Al component does not occur. Mineral particles from coal burning may be divided into Si-rich (quartz or silica glass), Pb-rich, Fe oxides, alumosilicates or alumosilicate glass and Na-rich particles (most likely a mechanical mixture of Si-rich particles with aged sea salt). The relative number abundance of these subgroups of mineral particles is highly variable. Mineral particles are rare in diesel burning, and seem to be mostly Fe oxides.The observed differences in minor element contents can be used in source apportionment studies for discrimination of individual soot particles as well as fly ash spheres from coal and diesel burning. The highly variable abundance of soot and of mineral particles (especially those consisting predominantly of toxic metals as for example Pb) should be taken into account in exposure assessment.

Santoro flame: The volume fraction of soot accounting for its morphology & composition

The soot volume fraction, fv, measured by Santoro and coworkers in an ethylene diffusion flame by light extinction has become a standard for validation of models for soot formation and growth. This fv, however, has been obtained assuming soot spheres of constant refractive index. As a result, when compared to that measured by microscopy and thermocouple particle densitometry (TPD) at identical conditions it is almost twice as much! This apparent disparity is resolved here by accounting for the detailed fractal-like structure and composition of soot through coupling discrete element modeling with the discrete dipole approximation to invert light extinction data and extract the fv. This is in good agreement with the fv from microscopy and TPD pointing out the benefit of accounting for the ramified soot morphology to close the soot mass balance and facilitate comparison of experiments with models for soot formation and growth.

A new understanding of the microstructure of soot particles: The reduced graphene oxide-like skeleton and its visible-light driven formation of reactive oxygen species.

The mechanisms of soot's photochemistry are still unclear, especially, how the microstructure and composition of soot influence its photoactivity. In the current study, we started with the exploration of the microstructure of soot particles and gained new insights. The elemental-carbon fraction of soot (E-soot), considered the core component of soot and can reflect the intrinsic characteristics of soot, was extracted by organic solvents and characterized in terms of structure and chemical reactivity. The intrinsic structure of E-soot was found to be more analogous to reduced graphene oxide than to graphene, in terms of containing similar levels of defective sites such as oxygen-containing functional groups and environmentally persistent free radicals, as well as exhibiting similar optoelectronic performance. The generation of reactive oxygen species via an electron transfer pathway under visible light suggests that reduced graphene oxide-like E-soot can serve as a potential carbo-photocatalyst, which facilitates elucidating the mechanism of E-soot's role during soot's photochemical aging. Our study reveals the intrinsic structure of soot and its role in photo-triggered reactive oxygen species production, which is vital for atmospheric and health effects.

Molecular content of nascent soot: Family characterization using two-step laser desorption laser ionization mass spectrometry

Molecules constituting nascent soot particles have been analyzed by two-step laser desorption laser ionization mass spectrometry. Three samples have been collected from a slightly sooting ethylene/air premixed flame with the aim to investigate soot composition in the transition from nucleated to just-grown soot particles. Sampling locations have been selected based on the evolution of the particle size distribution along the flame axis. The mass spectrometric results point to a strong evolution of the molecular composition. Just-nucleated soot is rich in polycyclic aromatic hydrocarbons (PAHs) dominated by medium sizes from 18 to 40 carbon atoms but containing sizes as large as 90 carbon atoms. Most abundant PAHs are in the form of peri-condensed structures. The presence of a large fraction of odd numbered carbon species shows that pentagonal cycles are a common feature of the detected population. Increasing the distance from the burner outlet, i.e., the particle residence time in flame, leads to an evolution of the chemical composition of this population with a major contribution of carbon clusters including also fullerenes up to about 160 carbon atoms. Our data support a scenario in which large PAHs containing pentagonal rings evolve very efficiently upon thermal processing by a series of dehydrogenation and isomerization processes to form fullerenes. This chemistry happens in the early steps of soot growth showing that carbonization is already active at this stage.

Determination of the volume fraction of soot accounting for its composition and morphology

The soot volume fraction, fv, is essential for combustion engineering, air quality and climate modeling. It is commonly obtained from mobility or optical data assuming soot spheres of constant composition that tend to overestimate fv by up to an order of magnitude. Here, a method is presented for estimation of the fv from soot mobility or optical diagnostics data accounting for the realistic soot morphology and composition. With mobility data, the fv is determined by a relation for soot morphology (fractal-like structure) and the average primary particle diameter from microscopy, gas adsorption or power laws. Such fv and the corresponding soot volume/mass size distributions are in excellent agreement with accurate but tedious soot mass-mobility measurements in premixed flames along various heights above the burner (HAB) as well as from the exhaust of diffusion flames and diesel engines. With light extinction data, the fv is obtained by explicitly accounting for soot composition (through its optical band gap and refractive index, RI) and the light absorption enhancement (due to multiple light scattering within soot agglomerates) in the absorption function, E(RI). So as nascent soot matures by surface growth and agglomeration, its optical band gap decreases while its mobility diameter, carbon to hydrogen (C/H) ratio and fv increase, increasing the soot E(RI) from 0.22 to 0.40, in excellent agreement with laser induced incandescence data from flat premixed ethylene flames. Using this variable E(RI), the soot fv from light extinction data in these flames is up to 50% lower than that using standard constant E(RI) for soot spheres.

Application of chemical graph theory to PAH isomer enumeration and structure in laser desorption/ionization mass spectrometry studies of particulate from an ethylene diffusion flame

Our laboratory recently published data that showed that the PAH composition of soot can be exactly determined and spatially resolved by low-fluence laser desorption ionization, coupled with high-resolution mass spectrometry imaging [1]. This analysis revealed that PAHs of 239–838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. In this paper, we demonstrate that the empirical formula of observed species can aid in the enumeration of isomers and places limits on their structures and thermodynamic stability. Specifically, chemical graph theory (CGT) shows that the vast majority of species observed in the sampled particulate matter may be described as benzenoid, consisting of only fused 6-membered rings. We apply CGT to determine the Dias Parameter, dS, for observed, individual PAH peaks and demonstrate that observed PAH species cluster near low dS, indicative of highly condensed structures, with relatively low populations of edge concavity (armchairs, bays, and fjords). Finally, we quantitatively explore the relative stability of PAH isomers using group-additivity estimates (for benzenoid structures) and those containing a single 5-membered rings using density functional theory. For the latter, we show that highly-condensed, benzenoid structures have lower free energy than those containing five-membered rings, with buried 5-membered rings showing the highest free energies.

Study of Technology for Preparing Titanium Carbide and Calcium Metal from Perovskite Concentrate by a Carbothermal Method

Substantiation of using a carbothermal method for processing flotation perovskite concentrate is presented. Results of X-ray structural studies of compacted specimens after two sintering stages are provided. It is shown that titanium carbide is formed in the first stage, and in the second stage calcium carbide is formed followed by dissociation into calcium metal and graphite. A dependence is obtained for the degree of transformation of titanium carbide on isothermal exposure duration and excess carbon in the initial charge. Dependence of degree of calcium extraction on isothermal exposure duration is demonstrated. It is shown that the temperature for the beginning of calcium carbidization at a given pressure is ≈ 1600°C. It is established that briquette compaction pressure has almost no effect on calcium extraction, while it affects briquette mechanical strength. Thermodynamic calculations of equilibrium compositions of phases in contact involved in production processes are performed using HSC Chemistry application software. Results of differential-thermal and thermogravimetric analyses of a charge of a given composition of flotation perovskite and soot are analyzed. In order to study kinetic regularities, correlation coefficients of isothermal exposure duration and reaction rate constant are calculated using kinetic equations of Yander, Gistling–Brownstein, Zhuravlev–Lesokhin–Tempel’man, anti-Gistling, anti-Yander, and Tamman. Apparent activation energy for the first stage of the carbothermal process is calculated using a specific model taking account of results of experiments conducted at different temperatures (Ea = 311.48 kJ/mol). It is established that the dependence obtained for the degree of transformation on isothermal exposure duration is most adequately described by an anti-Yander model formal kinetics equation. Optimum production conditions are selected for the process on the basis of research results: briquette pressing pressure is 8.57 MPa; first stage temperature 1500°C and 1750°C in the second stage; heating rate 17°C/min and 9°C/min respectively. In this case exposure time is 120 min and 60 min in the first and second stages, and residual pressure is 50 Pa and 13.3·10–3 Pa respectively.

Population balance modelling and laser diagnostic validation of soot particle evolution in laminar ethylene diffusion flames

Laminar diffusion flames present an elementary configuration for investigating soot formation and validating kinetic models before these are transferred to turbulent combustors. In the present article, we present a joint experimental and modelling investigation of soot formation in a laminar co-flow burner. The diffusion flames are analysed with the aid of laser diagnostic techniques, including elastic light scattering (ELS), planar laser-induced fluorescence of OH (OH-PLIF) and line-of-sight attenuation (LOSA), to measure the spatial distribution of soot, gas phase species and the line-of-sight integrated soot volume fraction (ISVF), respectively. The experimental dataset is supplemented by location-specific TEM images of thermophoretically sampled soot particles. The simulation of the sooting flames is carried out with a recently developed discretisation method for the population balance equation (Liu and Rigopoulos, 2019, Combust. Flame 205, 506-521) that accomplishes an accurate prediction of the particle size distribution, coupled with an in-house CFD code. By minimising numerical errors, we ensure that the discrepancies on the modelling side are mainly due to kinetics and are able to carry out an investigation of alternative models. We include a complete set of soot kinetics for PAH-based nucleation and condensation, HACA-based surface growth and oxidation as well as size-dependent aggregation, and consider three different gas phase reaction mechanisms (ABF, BBP and KM2). Based on predictions of the gas phase composition and particle size distribution of soot, modelled counterparts of the laser diagnostic signals are computed and compared with the experimental measurements. The approach of directly predicting signals circumvents the difficulties of explicitly representing the OH concentration in terms of the measured OH-PLIF data and avoids using ‘hybrid’ modelled and measured values to approximate the OH concentration. Moreover, the LOSA signal is directly converted to the line-of-sight ISVF instead of a measure of local soot volume fraction to avoid tomographic inversion errors. Lastly, the predicted ELS signal is computed in terms of the particle size distribution resolved by the population balance model, thus circumventing the approximation of an integral soot property using a presumed size distribution. While we cannot obtain quantitative agreement between experiments and simulations, the accuracy of the numerical approach and the direct prediction of experimental signals allow us to conduct sensitivity analyses of key empirical parameters and investigate the importance of the PAH chemistry and its influence on the competition between nucleation, condensation and surface growth.

Soot and char formation in the gasification of pig manure in a drop tube reactor

Biomass gasification offers a significant potential to close the loop of agriculture and many other activities that produce biomass residues. Pig manure, a residue produced in farms, has a huge pollutant potential due to its high production and chemical characteristics. It is necessary to take some control measures to decrease it, being pig manure gasification an interesting option. The present work studies the impact of the gasification temperature and atmosphere on the syngas composition (CO, H2, CH4 and CO2) and formation of soot and char in the gasification of pig manure in a drop tube furnace. The temperature varied between 900 and 1200 °C, and the gasification atmospheres included mixtures of O2/N2, O2/CO2/N2 and O2/H2O/N2. The results revealed that i) the syngas H2/CO ratio and its low heating value increase as the gasification temperature increases regardless of the gasification atmosphere; ii) the addition of H2O to the O2/N2 gasification atmosphere augments significantly the syngas H2/CO ratio, but does not enhance its low heating value, while the addition of CO2 increases slightly the H2/CO ratio, but significantly the heating value, iii) for the present reactor, the optimum operating conditions for the gasification of the pig manure in terms of syngas heating value and yield are a gasification temperature of 1200 °C and a gasification atmosphere composed of a mixture of O2/CO2/N2; and iv) soot yields increase as the temperature increases when gasification occurs in the O2/N2 and O2/CO2/N2 environments, remaining almost constant in the O2/H2O/N2 environment.

The Molecular Composition of Soot

AbstractSoot (sometimes referred to as black carbon) is produced when hydrocarbon fuels are burned. Our hypothesis is that polynuclear aromatic hydrocarbon (PAH) molecules are the dominant component of soot, with individual PAH molecules forming ordered stacks that agglomerate into primary particles (PP). Here we show that the PAH composition of soot can be exactly determined and spatially resolved by low‐fluence laser desorption ionization, coupled with high‐resolution mass spectrometry imaging. This analysis revealed that PAHs of 239–838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. As informed by chemical graph theory (CGT), the vast majority of species observed in the sampled particulate matter may be described as benzenoids, consisting of only fused 6‐membered rings. Within that limit, there is clear evidence for the presence of radical PAH in the particulate samples. Further, for benzenoid structures the observed empirical formulae limit the observed isomers to those which are nearly circular with high aromatic conjugation lengths for a given aromatic ring count. These results stand in contrast to recent reports that suggest higher aliphatic composition of primary particles.

The Molecular Composition of Soot.

Soot (sometimes referred to as black carbon) is produced when hydrocarbon fuels are burned. Our hypothesis is that polynuclear aromatic hydrocarbon (PAH) molecules are the dominant component of soot, with individual PAH molecules forming ordered stacks that agglomerate into primary particles (PP). Here we show that the PAH composition of soot can be exactly determined and spatially resolved by low-fluence laser desorption ionization, coupled with high-resolution mass spectrometry imaging. This analysis revealed that PAHs of 239-838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. As informed by chemical graph theory (CGT), the vast majority of species observed in the sampled particulate matter may be described as benzenoids, consisting of only fused 6-membered rings. Within that limit, there is clear evidence for the presence of radical PAH in the particulate samples. Further, for benzenoid structures the observed empirical formulae limit the observed isomers to those which are nearly circular with high aromatic conjugation lengths for a given aromatic ring count. These results stand in contrast to recent reports that suggest higher aliphatic composition of primary particles.