Carbonaceous Particulate Matter Research Articles

Carbon gas sensors synthesized using acacia auriculiformis tree branches to detect methanol, ethanol, acetone vapors and ammonia gas

Metal oxides and carbon are the prime candidates of gas sensor devices. For the inaugural instance, carbonaceous particulate matter was meticulously derived from the branches of Acacia auriculiformis tree indigenous to Sri Lanka to detect vapor and gas. It is worth noting that biomass derived carbon had hitherto remain unexplored in the realm of vapor and gas detection. Carbon films were fabricated via the doctor blade method. The resistivity characteristic of these carbon samples exhibited discernible variations upon exposure to methanol, ethanol, acetone vapors, and ammonia gas. Notably, the gas-sensing properties of sample derived from the central core and the outer shell of Acacia auriculiformis tree branches were independently assessed in these vapors and gas at ambient temperature. Various analytical techniques, including X-ray diffraction (XRD), UVvisible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), were judiciously employed to scrutinize the structural attribute, optical band gap, chemical composition and surface morphology of the aforementioned carbon film samples, respectively. XRD analyses unequivocally confirmed the successful formation of carbonaceous films. FTIR spectra conspicuously delineated the presence of oxygen within the carbon films. Importantly, the optical band gap of our carbon films manifested within the range characteristic of organic carbon. Furthermore, the resistance of the carbon films demonstrated a significant reduction upon adsorption of each vapor. It is noteworthy that while gas sensitivities and response times were superior for carbon derived from the central core of the Acacia tree branches, the recovery times were notably expedited for carbon synthesized from the outer shell of these branches. The zenith of gas sensitivity, an impressive 187%, was recorded in response to 1000 ppm of methanol vapor, when employing carbon sourced from the central core of the acacia tree branches.

Carbonaceous particulate matter promotes the horizontal transfer of antibiotic resistance genes.

There is growing concern about the transfer of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in airborne particulate matter. In this study, we investigated the effects of various types of carbonaceous particulate matter (CPM) on the transfer of ARGs in vitro. The results showed that CPM promoted the transfer of ARGs, which was related to the concentration and particle size. Compared with the control group, the transfer frequency was 95.5, 74.7, 65.4, 14.7, and 3.8 times higher in G (graphene), CB (carbon black), NGP (nanographite powder), GP1.6 (graphite powder 1.6 micron), and GP45 (graphite powder 45 micron) groups, respectively. Moreover, the transfer frequency gradually increased with the increase in CPM concentration, while there was a negative relationship between the CPM particle size and conjugative transfer frequency. In addition, the results showed that CPM could promote the transfer of ARGs by increasing ROS, as well as activating the SOS response and expression of conjugative transfer-related genes (trbBp, trfAp, korA, kroB, and trbA). These findings are indicative of the potential risk of CPM for the transfer of ARGs in the environment, enriching our understanding of environmental pollution and further raising awareness of environmental protection.

Daytime-nighttime variations in the concentration of PM0.1 carbonaceous particles during a biomass fire episode in Chiang Mai, Thailand

Carbonaceous aerosols affect air quality adversely, affect global warming, and human health. However, our understanding of the impact of ultrafine (PM0.1) carbonaceous particulate matter is incomplete, particularly the effects during haze episodes. This study monitored diurnal variations in PM0.1 in Chiang Mai, Thailand, from March to April 2020. We investigated carbonaceous PM0.1 collected by an ambient nano-sampler and evaluated their effect by using a carbon analyzer (IMPROVE_TOR). The results showed that burning large open areas in the dry season was crucial for increasing the particle mass concentration because of the large open burnings that occurred in this area. The majority of biomass fires near the sampling site occurred during the night, which would allow more particles to be released thus resulting in higher concentrations of PM0.1. Hence, the release of PM0.1 during the night would obviously result in higher concentrations than that during the day. In the eight carbon profiles, organic carbon 3 (OC3) was predicted to be a marker of biomass fires. The carbon indices displayed that PM0.1 was influenced by biomass burning both daytime and nighttime. The findings reported herein should be of great importance in terms of establishing biomass burning control policies for mitigating heavy haze pollution in Thailand and elsewhere.

Effect of Fire-deposited Charcoal on Soil Organic Carbon Pools and Associated Enzyme Activities in a Recently Harvested Pinus massoniana Plantation Subjected to Broadcast Burning

Charcoal is a carbonaceous particulate matter with a highly aromatic structure produced by incomplete combustion, and it can cause persistent long-term effects on soil ecological functions. In this study, we determined soil organic carbon pools and associated enzyme activities following five years of different charcoal treatments[charcoal removal (B0), charcoal retained in situ (B1), and the addition of charcoal removed from B0(B2)] and the unburnt control (UB) in a recently harvested Pinus massoniana plantation subjected to broadcast burning. The results showed that dissolved organic carbon (DOC), microbial biomass carbon (MBC), coarse and fine particulate organic carbon (CPOC and FPOC), and recalcitrant carbon (RC) contents were significantly lower in B1 than those in UB soil (P<0.05). The MBC and FPOC contents of B2 soil were comparable to those of UB soil, which were significantly higher than those of B0 soil (P<0.001). There was no difference in MBC/TC between the B2 and UB soils, whereas MBC/TC was significantly lower in B0 than in UB soil (P<0.05). β-glucosidase and peroxidase activities of B0, B1, and B2 soils were significantly lower than that of UB soil (P<0.01), and polyphenol oxidase activity was significantly lower in B0 and B2 soils than in UB soil (P<0.01). No significant difference in soil TC, DOC, readily oxidized carbon (ROC), CPOC, and RC content as well as associated enzyme activities was observed among the charcoal treatments (P>0.05). Redundancy analysis showed that sucrose and polyphenol oxidase were the key drivers influencing soil organic carbon fractions, accounting for 16.3% and 12.7% of the total variance, respectively. Overall, our findings indicated that fire-deposited charcoal played a positive role in enhancing soil microbial biomass carbon recovery, soil organic carbon accumulation, and stability, highlighting the importance of charcoal in the management of subtropical plantations in the future.

A comprehensive SERS, SEM and EDX study of individual atmospheric PM2.5 particles in Chengdu, China

Characterization of atmospheric fine particulate matter (PM2.5) in large cities has important implications for the study of their sources and formation mechanisms, as well as in developing effective measures to control air pollution. Herein, we report a holistic physical and chemical characterization of PM2.5 by combining surface-enhanced Raman scattering (SERS) with scanning electron microscopy (SEM) and electron-induced X-ray spectroscopy (EDX). PM2.5 particles were collected in a suburban area of Chengdu, a large city in China with a population over 21 million. A special SERS chip composed of inverted hollow Au cone (IHAC) arrays was designed and fabricated to allow direct loading of PM2.5 particles. SERS and EDX were used to reveal the chemical composition, and particle morphologies were analyzed from SEM images. SERS data of atmospheric PM2.5 indicated qualitatively the presence of carbonaceous particulate matter, sulfate, nitrate, metal oxides and bioparticles. The EDX showed the presence of the elements C, N, O, Fe, Na, Mg, Al, Si, S, K, and Ca in the collected PM2.5. Morphology analysis showed that the particulates were mainly in the form of flocculent clusters, spherical, regular crystal shaped or irregularly shaped particles. Our chemical and physical analyses also revealed that the main sources of PM2.5 are automobile exhaust, secondary pollution caused by photochemical reactions in the air, dust, emission from nearby industrial exhaust, biological particles, other aggregated particles, and hygroscopic particles. SERS and SEM data collected during three different seasons showed that carbon-containing particles are the principal sources of PM2.5. Our study demonstrates that the SERS based technique, when combined with standard physicochemical characterization methods, is a powerful analytical tool to determine the sources of ambient PM2.5 pollution. Results obtained in this work may be valuable to the prevention and control of PM2.5 pollution in air.

An overview on atmospheric carbonaceous particulate matter into carbon nanomaterials: A new approach for air pollution mitigation.

Air pollutants consisting of atmospheric particulate matter (PM) poses a major threat to the environment and human health. However, due to their carbonaceous nature, these atmospheric PM can also be used as a precursor for fabrication of high-valued carbon nanomaterials (CNMs) leading to waste to wealth as well as mitigation of air pollution. Over the few years, various results have been reported on different types of physical and chemical methods for the synthesis of CNMs from atmospheric particulate matter with the help of top down and bottom up methods; however, there is a lack of review on these innovative processes and outcome in order to assess their feasibility and suitability for further investigation. This review critically assesses the synthesis, identification, and characterization of different types of CNMs derived from the atmospheric PM. The fascinating fluorescence properties along with the novel multifarious applications of such PM-derived CNMs are also extensively discussed in this review work. This unique review will certainly help to make a new avenue for air pollution mitigation through conversion of PMs in to value added nanomaterials (VNMs) and will boost the research activity in the field of environmental nanotechnology for a cleaner environment.

Controlled Laboratory Generation of Atmospheric Black Carbon Using Laser Excitation-Based Soot Generator: From Basic Principles to Application Perspectives: A Review

The mimicking of atmospheric soot with versatile chemophysical properties is a critical issue in many applications, starting from instrument calibration, through producing aerosol standards for academic research, and ending with the reduction of uncertainties associated to carbonaceous particulate matter in the atmosphere, just to name a few. The present study deals with laser ablation as a novel and interesting technique for the generation of soot with high elementary carbon (EC) content with microphysical features similar to diesel or atmospheric soot and for modelling biomass emission under well-controlled laboratory conditions. The operation of the laser-excitation-based soot generator and the characteristics of the produced particles are compared to the most widely used techniques like flame, spark discharge generators, and real combustion soot originating from diesel- and aircraft engines or from field measurement. The comparison shows that significant differences in the physicochemical features exist between the real combustion soot and the soot originating from different excitation mechanisms. Moreover, the soot produced by different techniques shown also significant differences. However, due to some inherent and favorable attributes of the laser ablation technique—such as the possibility of the independent variation of physical characteristics of the generated soot particles—the potential for modelling biomass burning or to produce soot particles even in the accumulation mode makes it a useful tool in many cases.

Heterogeneous formation of EPFRs from aromatic adsorbates on the carbonaceous particulate matter

Pyrogenic carbonaceous materials of atmospheric particulate matter (PM) have recently aroused intensive interest, due to their critical role in the formation of environmentally persistent free radicals (EPFRs). This study focuses on the heterogeneous formation of EPFRs on the graphene oxide (GO), the dominant component of carbonaceous PM. First-principles calculations have been performed to investigate the interaction between 2-chlorophenol (2-CP), an important precursor of EPFRs, and GO to find the stable adsorption configurations. The climbing image nudged elastic band (CI-NEB) method and Dimer method were employed to explore the decomposition route of 2-CP to generate different types of EPFRs on the GO surface. The results indicate that aromatic precursors tend to undergo homolytic fission rather than heterolytic splitting to form EPFRs induced by surface oxygen-containing groups and carbon defects on the carbonaceous PM. Surface OH groups and water, both of which are related to ambient humidity, play essential roles in producing EPFRs. The formation mechanism of EPFRs over GO unveiled in this study, which represents dramatic differences from the conventional mechanism on the metal oxide surfaces, may account for a previously overlooked source of EPFRs encountered in atmospheric PM.

Emissions of Carbonaceous Particulate Matter and Ultrafine Particles from Vehicles-A Scientific Review in a Cross-Cutting Context of Air Pollution and Climate Change.

Airborne particulate matter (PM) is a pollutant of concern not only because of its adverse effects on human health but also on visibility and the radiative budget of the atmosphere. PM can be considered as a sum of solid/liquid species covering a wide range of particle sizes with diverse chemical composition. Organic aerosols may be emitted (primary organic aerosols, POA), or formed in the atmosphere following reaction of volatile organic compounds (secondary organic aerosols, SOA), but some of these compounds may partition between the gas and aerosol phases depending upon ambient conditions. This review focuses on carbonaceous PM and gaseous precursors emitted by road traffic, including ultrafine particles (UFP) and polycyclic aromatic hydrocarbons (PAHs) that are clearly linked to the evolution and formation of carbonaceous species. Clearly, the solid fraction of PM has been reduced during the last two decades, with the implementation of after-treatment systems abating approximately 99% of primary solid particle mass concentrations. However, the role of brown carbon and its radiative effect on climate and the generation of ultrafine particles by nucleation of organic vapour during the dilution of the exhaust remain unclear phenomena and will need further investigation. The increasing role of gasoline vehicles on carbonaceous particle emissions and formation is also highlighted, particularly through the chemical and thermodynamic evolution of organic gases and their propensity to produce particles. The remaining carbon-containing particles from brakes, tyres and road wear will still be a problem even in a future of full electrification of the vehicle fleet. Some key conclusions and recommendations are also proposed to support the decision makers in view of the next regulations on vehicle emissions worldwide.

Significant reduction in atmospheric organic and elemental carbon in PM2.5 in 2+26 cities in northern China

To better understand the change characteristics and reduction in organic carbon (OC) and elemental carbon (EC) in particulate matter (PM) with a diameter of ≤2.5 μm (PM2.5) driven by the most stringent clean air policies and pandemic-related lockdown measures in China, a comprehensive field campaign was performed to measure the carbonaceous components in PM2.5 on an hourly basis via harmonized analytical methods in the Beijing-Tianjin-Hebei and its surrounding region (including 2 + 26 cities) from January 1 to December 31, 2020. The results indicated that the annual average concentrations of OC and EC reached as low as 6.6 ± 5.7 and 1.8 ± 1.9 μg/m3, respectively, lower than those obtained in previous studies, which could be attributed to the effectiveness of the Clean Air Action Plan and the impact of the COVID-19-related lockdown measures implemented in China. Marked seasonal and diurnal variations in OC and EC were observed in the 2 + 26 cities. Significant correlations (p < 0.001) between OC and EC were found. The annual average secondary OC levels level ranged from 1.8–5.4 μg/m3, accounting for 37.7–73.0% of the OC concentration in the 2 + 26 cities estimated with the minimum R squared method. Based on Interagency Monitoring of Protected Visual Environments (IMPROVE) algorithms, the light extinction contribution of carbonaceous PM to the total amount reached 21.1% and 26.0% on average, suggesting that carbonaceous PM played a less important role in visibility impairment than did the other chemical components in PM2.5. This study is expected to provide an important real-time dataset and in-depth analysis of the significant reduction in OC and EC in PM2.5 driven by both the Clean Air Action Plan and COVID-19-related lockdown policies over the past few years, which could represent an insightful comparative case study for other developing countries/regions facing similar carbonaceous PM pollution.

Evolution of particulate matter deposited in the DPF channel during low-temperature regeneration by non-thermal plasma

In this paper, diesel particulate filters (DPFs) were regenerated at a low temperature (100 °C) using a non-thermal plasma (NTP) injection system. The physical and chemical characteristics of the particles deposited at different regeneration stages, such as their macromorphology, microstructure, oxidation activity, surface functional groups, and soluble organic fraction, were analyzed. The results showed that when NTP flowed through the DPF, the deposited particles were oxidized, decomposed, and then removed from the channels. The soot cake dispersed into blocks from an initially dense morphology and gradually shrank until it disappeared. The residual ash lost the initial spherical structure of the carbonaceous particulate matter (PM). The weak part of the flocculant structure of PM broke first during the oxidation of NTP active substances and decomposed into a chain structure. As DPF regeneration proceeded, O atoms were continuously bonded into the PM to form oxidation intermediate products that contained C-O, C=O, and other functional groups, which improved the PM oxidation activity. Changes in the physical and chemical properties of PM at the DPF regeneration interface were more significant than those at the most downstream sampling position. The high carbon atom fraction in the soluble organic fraction (SOF) decreased, and the DPF regeneration by NTP involved the continuous removal of carbon atoms.

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.

Distribution, Variations, Fate and Sources of Polycyclic Aromatic Hydrocarbons and Carbon in Particulate Matter, Road Dust, and Sediments in Central India

Pollution associated with polycyclic aromatic hydrocarbons (PAHs) and carbon emissions, resulting from fossil fuel combustion, is a matter of major concern in India. In this work, the distribution, variations, sources and fate of twelve PAHs (phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene) and carbonaceous particulate matter: elemental/black carbon (EC/BC), organic carbon (OC) and inorganic/carbonate carbon (CC) in the air, road dust and sediments of three cities in the most industrialized area of Central India (Chhattisgarh state) are reported. The PM, and road dust/sediment samples were collected by using low volume air sampler, and a stainless–steel scoop, respectively. PAHs were extracted into organic solvents and the dried residue was dissolved into acetonitrile for the analysis. Carbons, and PAHs were analyzed by thermal, and chromatographic methods. Concentrations of particulate matter (PM10), total carbon (TC = EC + OC + CC) and total polycyclic aromatic hydrocarbons (∑12PAHs) of 116–523 µg m−3, 22.1–179.6 µg m−3 and 37.7–164.9 ng m−3, respectively, were found in air at the beginning of the study (2007/08). Concentrations of 6.02 − 9.87% (TC) and 8689 − 87458 ng g−1 (Σ12PAHs) were detected in road dust, while relatively lower concentrations were observed in sediments, in the 4.99–10.78% and 4721–11768 ng g−1 range, respectively. Regarding monthly and seasonal variations, the highest PAHs and TC concentrations occurred in December/January and winter season. Spatial (residential, commercial, and industrial areas) and temporal (2008-2015) variations of these pollutants are also discussed, together with their source apportionment based on factor analysis. Given that benzo[a]pyrene and ∑12PAHs concentrations clearly exceed the permissible limits, and that the concentration of PAHs in dust for one of the three cities under study (Bhilai) is the highest reported in the literature, this study shows the urgent need of a continuous monitoring of organic aerosol constituents in the ambient air of the cities in this region.

Composition of particulate matter during a wildfire smoke episode in an urban area

The composition of wildfire smoke particulate matter (PM) was investigated during a 2018 smoke episode in the San Francisco Bay Area and compared to non-wildfire periods. Scanning electron microscopy (SEM) of passive PM samples deployed at four sites exhibited a higher concentration of submicron, spherical, carbonaceous PM (“tar balls”) during the wildfire period compared to the non-wildfire period. Coarse ash aluminosilicates and potassium bearing particles were enhanced as well. Disproportionately more UV light was absorbed by PM during the wildfire period than during the non-wildfire period, indicating a higher organic content consistent with the observed tar balls. An indoor PM sample from a residence operating a medium-efficiency furnace filter during the smoke episode exhibited fine, carbonaceous PM comparable to outdoors, but reduced coarse ash PM. Indoor/outdoor ratios for PM2.5, PM10-2.5, and PM10 were 0.6, 0.1, and 0.5 respectively. SEM of the wildfire furnace filter revealed a greater proportion of tar balls compared to a non-wildfire filter. Relatively rare particles enriched in Cu, Zn, Sn and Pb were observed in wildfire samples, but not in non-wildfire samples. Higher concentrations of Cu, Zn, and Pb during the wildfire were confirmed by inductively coupled plasma mass spectrometry (ICP-MS) of the furnace filter. The use of low-cost passive samplers enabled rapid deployment at multiple locations and indoors and outdoors during the wildfire episode. These measurements suggest smoke impacts were regional in scale and similar across sites, though local variations in PM2.5 magnitudes, particle types, and confounding by local sources were observed.Copyright © 2021 American Association for Aerosol Research

Comparative Toxic Effects of Manufactured Nanoparticles and Atmospheric Particulate Matter in Human Lung Epithelial Cells.

Although nanoparticles (NPs) have been used as simplified atmospheric particulate matter (PM) models, little experimental evidence is available to support such simulations. In this study, we comparatively assessed the toxic effects of PM and typical NPs (four carbonaceous NPs with different morphologies, metal NPs of Fe, Al, and Ti, as well as SiO2 NPs) on human lung epithelial A549 cells. The EC50 value of PM evaluated by cell viability assay was 148.7 μg/mL, closest to that of SiO2 NPs, between the values of carbonaceous NPs and metal NPs. All particles caused varying degrees of reactive oxygen species (ROS) generation and adenosine triphosphate (ATP) suppression. TiO2 NPs showed similar performance with PM in inducing ROS production (p < 0.05). Small variations between two carbonaceous NPs (graphene oxides and graphenes) and PM were also observed at 50 μg/mL. Similarly, there was no significant difference in ATP inhibition between carbonaceous NPs and PM, while markedly different effects were caused by SiO2 NP and TiO2 NP exposure. Our results indicated that carbonaceous NPs could be served as potential surrogates for urban PM. The identification of PM model may help us further explore the specific roles and mechanisms of various components in PM.

Prostaglandin E2 and phagocytosis of inhaled particulate matter by airway macrophages in cystic fibrosis

BackgroundExposure to particulate matter (PM) air pollution is associated with adverse health outcomes in children with cystic fibrosis (CF). Airway macrophages (AM) phagocytose and retain inhaled PM in vivo, and the area of carbon in AM reflects both inhaled PM dose and phagocytic function. Since airway prostaglandin-E2 (PGE2) is increased in CF, and PGE2 suppresses AM phagocytosis, we sought evidence for PGE2-mediated suppression of AM phagocytosis of inhaled carbonaceous PM in CF. MethodsAfter informed consent, urine was obtained from 20 controls and 24 CF children. In the subgroup of older children, at least one induced sputum was done in 20 controls and 19 CF children. Urinary tetranor PGEM, the major metabolite of PGE2, and sputum PGE2 were measured by mass spectrometry. The area of carbon in AM was determined by image analysis. Exposure to PM was assessed by modelling and personal monitoring. The effect of either PGE2 or CF sputum supernatant on phagocytosis of diesel exhaust particle (DEP) by AM was assessed in vitro. Data were analysed by t-test. ResultsBoth urinary tetranor PGEM (P<0.05), and sputum PGE2 (P<0.05) were increased in CF . Despite no difference in PM exposure between groups, the area of phagocytosed carbon by AM was decreased in children with CF (P<0.01). PGE2 suppressed phagocytosis of DEP by AM from both controls and CF (P<0.0001). CF sputum supernatant suppressed phagocytosis of DEP by AM (P<0.0001) in a PGE2-dependent manner. ConclusionIncreased PGE2 in the CF airway suppresses phagocytosis of inhaled PM by AM.

Occurrence of both nonvolatile and semivolatile carbonaceous air particulate markers using thermal desorption-pyrolysis-gas chromatography-mass spectrometry

Particulate matter (PM) occurring in the atmosphere is a complex mix of organic species that originate from many sources due to long range transport. Many anthropogenic and biogenic sources have unique chemical components that enable their use as atmospheric markers of emissions. Application of thermal desorption–pyrolysis coupled with gas chromatography-mass spectrometry (TD-Pyr-GC-MS) enabled the characterization of both semivolatile and nonvolatile atmospheric markers in PM, both of which are difficult to characterize using traditional TD or solvent extraction alone. The nonvolatile organic PM fraction was found to be significant based on thermal optical analysis (TOA) quantification, with 73–87% of organic carbon (OC) evolving at temperatures above 400 °C (i.e., Pyr). The semivolatile organic carbon (SVOC) fraction (i.e., TD) of PM featured distinct profiles of alkanes, fatty acids, fatty acid methyl esters and 2-ring polycyclic aromatic hydrocarbons (PAHs), mostly associated with biogenic origin. By contrast, in the Pyr fractions of carbonaceous PM, highly abundant homologous series of n-alkenes, n-alkylbenzenes, PAHs, n-alkanes, and substituted phenols were identified. The occurrence of these compounds is conveyed through newly developed pyrolytic indicators reflecting the breakdown of biogenic sources, e.g., plant lipids, although certain sampling periods showed a contribution of anthropogenic origin. These previously unresolved biogenic and anthropogenic Pyr profiles provide a more representative characterization of atmospheric PM that can help in identifying emission sources.

Near infrared hyperspectral imaging as a tool for quantifying atmospheric carbonaceous aerosol

The quantitative determination of atmospheric organic carbon (OC), elemental carbon (EC) and total carbon (TC) is of utmost relevance due to its influence on global warming, visibility degradation, and human health. Thermal-optical transmission (TOT) is the most common analytical method used to analyze them. Nevertheless, it is destructive, time-consuming, and only a small portion of the sample is analyzed. Here, near infrared spectroscopy coupled with a hyperspectral detector (HSI-NIR), together with multivariate data analysis, comes as a reliable alternative.This work aims at establishing a methodology for the quantitation of the carbonaceous content in atmospheric particulate matter (PM) fusing HSI-NIR and multivariate data analysis, and being validated with TOT analysis. Principal Component Analysis and Multivariate Curve Resolution analysis, used as qualitative tools, confirmed concentration trends in the PM samples, and contributions from the chemical composition of both the filter material and aerosol samples. The Partial Least Squares (PLS) regression models developed were optimized using interval Partial Least Squares (iPLS) selection and showed a high correlation between the HSI-NIR spectra and TOT measurements: R2Cal = 0.99, 0.94 and 0.99 for the OC, EC and TC contents, respectively. Finally, the spatial distribution of the carbonaceous content in the filter samples was assessed using a homogeneity percentage (%H). This showed values higher than 50% for all cases, which indicated that no distributional inhomogeneities were observed in the filters and corroborated the efficient operation of the sampling system. This study demonstrated the feasibility of using HSI-NIR for the quantitative assessment of carbonaceous particulate matter in air pollution monitoring.

Influence of Ash-Soot Interactions on the Reactivity of Soot from a Gasoline Direct Injection Engine.

Gasoline particulate filters (GPF) are being utilized in certain markets on gasoline direct injection (GDI) vehicles to reduce tailpipe particulate emissions as required by particle number regulations. GPF filtration efficiency is dependent on soot build-up within the filter. Since soot oxidizes within the GPF during normal vehicle operation, an understanding of soot reactivity is important for optimizing aftertreatment architecture and engine calibration. Past work has indicated that gasoline soot reactivity may depend on levels of metallic ash species. In this work, carbonaceous particulate matter from a GDI engine are evaluated from engine operation at a consistent speed and load but with different levels of fuel injection pressures and timings to vary the relative ash to soot ratio. Soot reactivity is found to vary significantly with the ratio of ash to soot present. Interestingly, the more reactive soots possess a unique oxidation profile by which a conventional Arrhenius type expression cannot be used to quantify reactivity. To understand the mechanisms driving such distinct oxidation differences, soot samples are analyzed after being partially oxidized. Particulate characteristics are evaluated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM + EDS). A mechanism is proposed that may explain further why ash affects gasoline soot reactivity to the extent seen in this and other work.

Effects of coal types and combustion conditions on carbonaceous aerosols in flue gas and their light absorption properties

Under typical Chinese wintry rural conditions, dominating individual coal heating would emit lots of the fine fraction of ambient aerosol exclusively including carbonaceous particulate matter. In this study, a specified drop tube furnace system is employed to simulate experimentally particle matter emitted during individual coal combustion. Emphatically, the effects of coal types, oxygen concentration and combustion ambient on the formation characteristics of carbonaceous aerosols in the flue gas were discussed. It was found that the fraction of organic carbon (OC) and elemental carbon (EC) in the flue gas produced by bituminous coal combustion was lower than that of lignite. Meanwhile, with the increase of oxygen concentration, the production of OC and EC decreased, but the sensitivity of EC to oxygen concentration was higher than that of OC, which indicated that the formation mechanism of OC and EC is extremely different. Noticeable, the Absorption Ångström Exponent (AAE) of methanol-soluble organic carbon (MSOC) is higher than that of water-soluble organic carbon (WSOC), which indicates that a large amount of methanol-soluble but water-insoluble brown carbon has strong light absorption capacity between 330 nm and 550 nm, and its light absorption capacity tends to be in the short-wave region. The mass absorption efficiency (MAE) of brown carbon produced by coal combustion (0.1–1 m2/gC) is similar to that of atmospheric aerosol (0.3–1.8 m2/gC), which indicates that the contribution of brown carbon emitted from coal combustion to the light absorption capacity of atmospheric aerosol should not be underestimated.