Polycyclic Aromatic Hydrocarbon Emission Research Articles

Characterization and risk assessment of polycyclic aromatic hydrocarbons (PAHs) pollution in particulate matter in rural residential environments in China-A review

In recent years, air pollution in rural residential environments in China has received significant attention, with polycyclic aromatic hydrocarbons (PAHs) pollution being particularly important which is associated with various health problems. Although some studies have investigated indoor air pollution in rural China, a comprehensive exploration of PAHs pollution has not been completed. Therefore, this study screened peer-reviewed Chinese and English articles on PAHs in indoor particulate matter in rural China published between January 1, 2010, and September 30, 2022, and retrieved a total of 2010 papers. After selection criteria, 24 papers were ultimately chosen for data extraction and comprehensive analysis. The results showed that the level of PAHs pollution in rural residential environments in China was 1408.27±1888.85 ng/m3 (62.17∼6606.53 ng/m3). The kitchen was the most severely polluted area in households, with pollution levels highest in the spring and winter. The use of clean energy to replace traditional solid fuels can significantly reduce PAH emissions, but most households still use a mixture of fuels, and the level of PAH pollution remains high. It is worth emphasizing that the cancer risk assessment indicated that rural Chinese residents' total incremental lifetime cancer risk (TILCR) was greater than 10−4, indicating a high risk of cancer. This study provides accurate information on the current status of PAHs pollution in indoor particulate matter in rural China, which will serve as a solid foundation for future prevention and control efforts.

Polycyclic Aromatic Hydrocarbons in Air and Dust Samples from Vietnamese End-of-life Vehicle Processing Workshops: Contamination Status, Sources, and Exposure Risks.

Concentrations of 18 unsubstituted polycyclic aromatic hydrocarbons (PAHs) and 11 methylated derivatives (Me-PAHs) were measured in polyurethane foam-based passive air (PUF-PAS) and settled dust samples collected from end-of-life vehicle (ELV) processing workshops in northern Vietnam. Concentrations of total 29 PAHs ranged from 42 to 95 (median 57) ng/m3 and from 860 to 18,000 (median 5700) ng/g in air and dust samples, respectively. PAH levels in ELV air and dust samples were 1.5 ± 0.4 and 9.4 ± 7.9 times higher than levels found in a control house, suggesting ELV processing as potential PAH emission sources. Concentrations and proportions of Me-PAHs in total PAHs of the ELV air (26% ± 7%) and dust (41% ± 14%) were higher than those found in control house (18% in both air and dust). The occurrence of PAHs and Me-PAHs in the ELV workshops are attributed to not only pyrogenic but also petrogenic sources (i.e., improper treatment and management of fuels, lubricants, and vehicle oils).

A Diverse Population of z ∼ 2 ULIRGs Revealed by JWST Imaging

Four ultraluminous infrared galaxies (ULIRGs) observed with JWST/NIRcam in the Cosmos Evolution Early Release Science program offer an unbiased preview of the z ∼ 2 ULIRG population. The objects were originally selected at 24 μm and have strong polycyclic aromatic hydrocarbon emission features observed with Spitzer/Infrared Spectrometer. The four objects have similar stellar masses of ∼1011 M ⊙ but otherwise are quite diverse. One is an isolated disk galaxy, but it has an active nucleus as shown by X-ray observations and by a bright point-source nucleus. Two others are merging pairs with mass ratios of 6–7:1. One has active nuclei in both components, while the other has only one active nucleus: the one in the less-massive neighbor, not the ULIRG. The fourth object is clumpy and irregular and is probably a merger, but there is no sign of an active nucleus. The intrinsic spectral energy distributions for the four active galactic nuclei in these systems are typical of type-2 QSOs. This study is consistent with the idea that even if internal processes can produce large luminosities at z ∼ 2, galaxy merging may still be necessary for the most luminous objects. The diversity of these four initial examples suggests that large samples will be needed to understand the z ∼ 2 ULIRG population.

Genotoxicity by rapeseed methyl ester and hydrogenated vegetable oil combustion exhaust products in lung epithelial (A549) cells.

Biofuel is an attractive substitute for petrodiesel because of its lower environmental footprint. For instance, the polycyclic aromatic hydrocarbons (PAH) emission per fuel energy content is lower for rapeseed methyl ester (RME) than for petrodiesel. This study assesses genotoxicity by extractable organic matter (EOM) of exhaust particles from the combustion of petrodiesel, RME, and hydrogenated vegetable oil (HVO) in lung epithelial (A549) cells. Genotoxicity was assessed as DNA strand breaks by the alkaline comet assay. EOM from the combustion of petrodiesel and RME generated the same level of DNA strand breaks based on the equal concentration of total PAH (i.e. net increases of 0.13 [95% confidence interval (CI): 0.002, 0.25, and 0.12 [95% CI: 0.01, 0.24] lesions per million base pairs, respectively). In comparison, the positive control (etoposide) generated a much higher level of DNA strand breaks (i.e. 0.84, 95% CI: 0.72, 0.97) lesions per million base pairs. Relatively low concentrations of EOM from RME and HVO combustion particles (<116 ng/ml total PAH) did not cause DNA strand breaks in A549 cells, whereas benzo[a]pyrene and PAH-rich EOM from petrodiesel combusted using low oxygen inlet concentration were genotoxic. The genotoxicity was attributed to high molecular weight PAH isomers with 5-6 rings. In summary, the results show that EOM from the combustion of petrodiesel and RME generate the same level of DNA strand breaks on an equal total PAH basis. However, the genotoxic hazard of engine exhaust from on-road vehicles is lower for RME than petrodiesel because of lower PAH emission per fuel energy content.

Emission factors for a biofuel impacted fleet in South America's largest metropolitan area

The Metropolitan Area of São Paulo (MASP) is among the largest urban areas in the Southern Hemisphere. Vehicular emissions are of great concern in metropolitan areas and MASP is unique due to the use of biofuels on a large scale (sugarcane ethanol and biodiesel). In this work, tunnel measurements were employed to assess vehicle emissions and to calculate emission factors (EFs) for heavy-duty and light-duty vehicles (HDVs and LDVs). The EFs were determined for particulate matter (PM) and its chemical compounds. The EFs obtained for 2018 were compared with previous tunnel experiments performed in the same area. An overall trend of reduction of fine and coarse PM, organic carbon (OC), and elemental carbon (EC) EFs for both LDVs and HDVs was observed if compared to those observed in past years, suggesting the effectiveness of vehicular emissions control policies implemented in Brazil. A predominance of Fe, Cu, Al, and Ba emissions was observed for the LDV fleet in the fine fraction. Cu presented higher emissions than two decades ago, which was associated with the increased use of ethanol fuel in the region. For HDVs, Zn and Pb were mostly emitted in the fine mode and were linked with lubricating oil emissions from diesel vehicles. A predominance in the emission of three- and four-ring polycyclic aromatic hydrocarbons (PAHs) for HDVs and five-ring PAHs for LDVs agreed with what was observed in previous studies. The use of biofuels may explain the lower PAH emissions for LDVs (including carcinogenic benzo[a]pyrene) compared to those observed in other countries. The tendency observed was that LDVs emitted higher amounts of carcinogenic species. The use of these real EFs in air quality modeling resulted in more accurate simulations of PM concentrations, showing the importance of updating data with real-world measurements.

Influence of Atmosphere and Temperature on Polycyclic Aromatic Hydrocarbon Emissions from Green Anode Paste Baking.

Coal tar pitch, a well-known source of polycyclic aromatic hydrocarbons (PAHs), is used as a binder of petroleum coke in prebaked anodes used for electrolysis of aluminum. Anodes are baked up to 1100 °C over a 20-day period, where flue gas containing PAHs and volatile organic compounds (VOCs) are treated using techniques such as regenerative thermal oxidation, quenching, and washing. Conditions during baking facilitate incomplete combustion of PAHs, and due to the various structures and properties of PAHs, the effect of temperature up to 750 °C and various atmospheres during pyrolysis and combustion were tested. PAH emissions from green anode paste (GAP) dominate in the temperature interval of 251-500 °C, where PAH species of 4-6 rings make up the majority of the emission profile. During pyrolysis in argon atmosphere, a total of 1645 μg EPA-16 PAHs are emitted per gram of GAP. Adding 5 and 10% CO2 to the inert atmosphere does not seem to affect the PAH emission level significantly, at 1547 and 1666 μg/g, respectively. When adding oxygen, concentrations decreased to 569 μg/g and 417 μg/g for 5% and 10% O2, respectively, corresponding to a 65% and 75% decrease in emission.

Analysis of Polycyclic Aromatic Hydrocarbon Emissions from a Pilot Scale Silicon Process with Flue Gas Recirculation

Flue gas recirculation (FGR) is a method used in several industries to control emissions and process conditions, such as NOx reduction and temperature levels, and increase the CO2 concentration in the off-gas, to be better suited for methods of carbon capture. In this study, the influence of FGR, varying levels of flue gas flow and oxygen concentration on the emissions of polycyclic aromatic hydrocarbons (PAHs) was investigated during Si alloy production. In addition, computational fluid dynamics (CFD) modeling was performed using OpenFOAM for combustion of C2H2 and H2 with varying O2 levels to simulate FGR and to gain better insight into the impact of furnace operations on the PAH evolution. Experimental results show that increasing FGR (0–82.5%) and decreasing levels of oxygen (20.7–13.3 vol %) increase the PAH-42 concentration from 14.1 to 559.7 μg/Nm3. This is supported by the simulations, where increased formation of all PAHs species was observed at high levels of FGR, especially for the lighter aromatic species (like benzene and naphthalene), due to the lower availability of oxygen and the reduction in temperature. Residence time was identified as another key parameter to promote complete combustion of PAHs. Benzene oxidation can be prevented with temperatures lower than 1000 K and residence times smaller than 1 s, while complete oxidation is found at temperatures of around 1500 K.

Health Risk Assessment of Polycyclic Aromatic Hydrocarbons from Cooking Fuels burning in Nigeria

Cooking activities are an important source of indoor air pollution which contributes significantly to Polycyclic Aromatic Hydrocarbons (PAHs) in the environment. This study investigated sixteen (16) priority PAHs emitted from smoke in eight (8) cooking fuels commonly used in Nigeria. Gas Chromatography Mass Spectrometry (GC-MS) was used for sample analysis and the potential health risk associated with exposure to PAHs were evaluated. The highest total quantified PAHs concentration was obtained from the burning of palm kernel fiber with an average ΣPAHs of 14.06 mg/kg. The result showed a variation in the average concentration of 10.82 − 14.06 mg/kg for all the cooking fuels. 3-ringed PAHs were found to be the dominant PAHs in the samples considered in terms of concentrations and frequency of occurrence at 7.03-9.42 mg/kg. Benzo[a]anthracene was the most abundant PAHs in biomass materials while Benzo[a]pyrene was the most abundant in liquified petroleum gas and Benzo[b]fluoranthene in kerosene. The cancer risk for both the children and adult obtained for all the cooking fuel samples were less than 10 − 6 which is satisfactory except in sawdust which has a value of 1.30 × 10 − 5 and 1.44 × 10 − 5 for child and adult, respectively. It is recommended that cleaner cooking fuels be used in well-ventilated environments to reduce exposure to these pollutants. Highlights Sixteen priority PAHs in emissions from the burning of eight cooking fuels in Nigeria were investigated Emission sources of the PAHs were identified using diagnostic ratios Health risks of PAHs in emissions from the burning of cooking fuels is higher in adult

Influence of Fuel Oxygenation on Regulated Pollutants and Unregulated Aromatic Compounds with Biodiesel and n-Pentanol Blends

It is very important to determine the polycyclic aromatic hydrocarbon (PAH) emissions caused by the use of renewable fuels in diesel engines and to know the possible damages. This study investigates the emissions (regulated and unregulated) of biodiesel/n-pentanol mixtures, which are free of aromatic content, with emphasis on PAH formation and an examination of toxicity to public health and the environment. Engine failures caused by wetstacking are also discussed. Biodiesel/n-pentanol fuel mixtures with alcohol concentrations of 5%, 20%, and 35% by volume (v/v) served as test fuels in a compression ignition engine. A five-gas analyzer was used to measure hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions. Polycyclic aromatic hydrocarbons were detected and measured using gas chromatography-mass spectrometry (GC-MS). Against the baseline diesel fuel, the biodiesel/n-pentanol fuel blends and neat biodiesel reduced NOx emissions and produced significantly fewer PAHs and toxicity, confirming the significance of the aromatic content of the fuel. Biodiesel reduced total PAHs by 48.02% and the addition of 5% n-pentanol to biodiesel further decreased total PAHs by 21.26%. The total toxicity (BaPeq (benzo[a]pyrene equivalent)) as a result of biodiesel was 83.49% less than diesel. The addition of n-pentanol to biodiesel further reduced toxicity by 59.15%, 57.89%, and 48.33% for BPen5, BPen20, and BPen35 blends, respectively. In addition, n-pentanol was shown to be effective for reducing total PAH emissions, as well as heavier PAHs, which have greater carcinogenicity and pose a greater likelihood of engine damage from wetstacking when running in low-load conditions at cold temperatures.

Bitumen fumes and PAHs in asphalt road paving: Emission characteristics, determinants of exposure and environmental impact

BackgroundAsphalt road paving and its subsequent complex airborne emissions have raised concerns about occupational exposures and environmental impacts. Although several studies described bitumen fumes or Polycyclic Aromatic Hydrocarbons (PAH) emissions at specific worksites, no comprehensive studies have characterised road paving emissions and identified the main determinants of exposure. MethodsA 10-year study from 2012 to 2022 was performed to examine the pollutants resulting from bitumen fume emissions and covering the main processes used in road paving (asphalt production, mechanical rolled asphalt paving, manual paving, mastic asphalt paving, emulsion paving, and coal-tar asphalt milling). A total of 623 air samples were collected at 63 worksites (on 290 workers, in the environment and near emission sources), and bitumen fumes, PAHs, aldehydes and volatile organic compounds were analysed. Biomonitoring campaigns were performed on 130 workers to assess internal exposure to PAHs. ResultsFume emissions revealed complex mixtures of C10–C30 compounds, including linear saturated hydrocarbons (C6–C12), alicyclic hydrocarbons and aliphatic ketones. PAHs were dominated by 2–3 aromatic ring compounds (naphthalene, fluorene, and phenanthrene), and C1–C13 aldehydes were identified. Binder proportion, paving temperature, outdoor temperature, workload and job category influenced airborne concentrations. A significant temporal trend was observed over the time period of the study, with decreasing BF and PAH exposures. PAH biomonitoring was consistent with air samples, and urinary metabolites of 2–3 ring PAHs dominated over 4–5 ring PAHs. Occupational exposures were generally far lower than exposure limits, except coal-tar asphalt milling activities. Very low environmental concentrations were measured, which highlights a negligible contribution of paving emissions to global environmental pollution. ConclusionThe present study confirmed the complex nature of bitumen fumes and characterised the main determinants of exposure. The results highlight the need to reduce the paving temperature and binder proportion. Recycled asphalt pavement use was not associated with higher emissions. The impact of paving activities on environmental airborne pollution was deemed negligible.

PAH Emission from Star-forming Galaxies in JWST Mid-infrared Imaging of the Lensing Cluster SMACS J0723.3-7327

The mid-infrared spectra of star-forming galaxies (SFGs) are characterized by characteristic broad polycyclic aromatic hydrocarbon (PAH) emission features at 3–20 μm. As these features are redshifted, they are predicted to dominate the flux at specific mid-infrared wavelengths, leading to substantial redshift-dependent color variations in broadband photometry. The advent of JWST for the first time allows the study of this effect for normal SFGs. Based on spectral energy distribution templates, we here present tracks in mid-infrared (4.4, 7.7, 10, 15, and 18 μm) color–color diagrams describing the redshift dependence of SFG colors. In addition, we present simulated color–color diagrams by populating these tracks using the cosmic star formation history and the star formation rate function. Depending on redshift, we find that SFGs stand out in the color–color diagrams by several magnitudes. We provide the first observational demonstration of this effect for galaxies detected in the JWST Early Release Observations of the field toward the lensing cluster SMACS J0723.3−7327. While the distribution of detected galaxies is consistent with the simulations, the numbers are substantially boosted by lensing effects. The PAH emitter with the highest spectroscopic redshift, detected in all bands, is a multiply imaged galaxy at z = 1.45. There is also a substantial number of cluster members that do not exhibit PAH emission except for one SFG at z = 0.38. Future wider-field observations will further populate mid-infrared color–color diagrams and provide insight into the evolution of typical SFGs.

Investigating industrial PAH air pollution in relation to population exposure in major countries: A scoring approach

Polycyclic aromatic hydrocarbons (PAHs) are common air pollutants worldwide, associated with industrial processes. In the general population, both modeling and field studies revealed a positive correlation between air PAH concentrations and urinary PAH metabolite levels. Many countries lack population urinary data that correspond to local PAH air concentrations. Thus, we proposed a scoring-based approximate approach to investigating that correlation in selected countries, hypothesizing that PAH air concentrations in selected regions could represent the national air quality influenced by industrial emission and further correlate to PAH internal exposure in the general population. This research compiled 85 peer-reviewed journal articles and 9 official monitoring datasets/reports covering 34 countries, 16 of which with both atmospheric PAH data and human biomonitoring data. For the air pollution score (AirS), Egypt had the highest AirS at 0.94 and Pakistan was at the bottom of the score ranking at −1.95, as well as the median in the UK (AirS: 0.50). For the population exposure score (ExpS), China gained the top ExpS at 0.44 and Spain was with the lowest ExpS of −1.52, with the median value in Italy (ExpS: 0.43). Through the correlation analysis, atmospheric PAHs and their corresponding urinary metabolites provided a positive relationship to a diverse extent, indicating that the related urinary metabolites could reflect the population's exposure to specific atmospheric PAHs. The findings also revealed that in the 16 selected countries, AirS indexes were positively correlated with ExpS indexes, implying that higher PAH levels in the air may lead to elevated metabolite urinary levels in general populations. Furthermore, lowering PAH air concentrations could reduce population internal PAH exposure, implying that strict PAH air regulation or emission would reduce health risks for general populations. Notably, this study was an ideal theoretical research based on proposed assumptions to some extent. Further research should focus on understanding exposure pathways, protecting vulnerable populations, and improving the PAH database to optimize PAH pollution control.

Determination of carbonyls and size-segregated polycyclic aromatic hydrocarbons, and their nitro and alkyl analogs in emissions from diesel–biodiesel-ethanol blends

This study characterizes carbonyls (RCHO), polycyclic aromatic hydrocarbons (PAHs), their nitrated (nitro-PAHs) and alkylated (alkyl-PAHs) in particulate matter in the exhaust emissions of a diesel engine. The measurements were made with a standard engine, often found in vans used in Brazil, fueled with pure commercial diesel and mixtures of 10, 20, and 30% biodiesel with 2, 4, and 6% of ethanol. Particulate matter sampling was carried out with a 10-stage cascade impactor. Chemical analyses for PAHs and their derivatives were conducted using gas phase chromatography-mass spectrometry (GC/MS). RCHO were sampled using impingers with 2,4-DNPH and analyzed using HPLC with UV detection. The results showed that emissions of all the PAHs and their derivatives were reduced with the use of biodiesel and ethanol, with the exception of the blend of 30% biodiesel with 4% ethanol. However, all the RCHO emissions increased with biodiesel and ethanol. High correlations were observed between the emissions of PAHs, alkyl-PAHs and nitro-PAHs, which suggests a similarity in the formation mechanisms of these compounds. All PAHs' emissions have a strong negative correlation with biodiesel content and with RCHO emissions and a medium correlation with ethanol content. In contrast, biodiesel and ethanol with the RCHO emissions lead to a positive correlation coefficient of these compounds which is more pronounced for biodiesel than ethanol.

Parent and alkylated polycyclic aromatic hydrocarbon emissions from coal seam fire at Wuda, Inner Mongolia, China: characteristics, spatial distribution, sources, and health risk assessment.

The Wuda coalfield in Inner Mongolia is a vital coal base in China, and it is the hardest-hit area for coal fires (spontaneous combustion of coal seams and coal gangue). Using gas chromatography-mass spectrometry, this work tested the concentration and analyzed the characteristics, distribution, sources, and health risks of polycyclic aromatic compounds (PACs) in the surface soil of the Wuda District, including the coal mine, coal fire, agricultural, and background areas. The soil of coal mine and coal fire area were heavily polluted with PACs, with mean concentrations of 9107 and 3163µgkg-1, respectively, considerably higher than those in the agricultural (1232µgkg-1) and background areas (710µgkg-1). Alkyl polycyclic aromatic hydrocarbons (APAHs) were the dominant pollutants among these PACs, accounting for 60-81%. Alkyl naphthalenes and alkyl phenanthrenes are the primary pollutants in APAHs, accounting for 80-90% of the total amounts. Additionally, using the positive matrix factorization method, it can be concluded that the primary PAC sources are petrogenic sources, coal and biomass combustion, coal fires, and vehicle emissions. Finally, according to the cancer risk values of 16 PAHs, only the coal mine area showed a potential cancer risk. However, this result lacks a risk assessment of APAHs and underestimates the actual risk. The results of this study improved the understanding of PAC pollution in coal fire and surrounding areas and provided a reference for environmental and health risk investigations.

Characterization of Gaseous and Particulate Phase Polycyclic Aromatic Hydrocarbons Emitted During Preharvest Burning of Sugar Cane in Different Regions of Kwa-Zulu Natal, South Africa.

Biomass burning is a significant anthropogenic source of air pollution, including the preharvest burning of sugar cane. These burn events result in atmospheric emissions, including semivolatile organic compounds, that may have adverse impacts on air quality and human health on a local, regional, and even a global scale. Gaseous and particulate polycyclic aromatic hydrocarbon (PAH) emissions from various sugar cane burn events in the province of Kwa-Zulu Natal in South Africa were simultaneously sampled using a portable denuder sampling technology, consisting of a quartz fiber filter sandwiched between two polydimethylsiloxane multichannel traps. Total gas and particle phase PAH concentrations ranged from 0.05 to 9.85 µg m-3 per individual burn event, and nine PAHs were quantified. Over 85% of all PAHs were found to exist in the gas phase, with smaller two- and three-ring PAHs, primarily naphthalene, 1-methyl naphthalene, and acenaphthylene, being the most dominant and causing the majority of variance between the burn sites. The PAH profiles differed between the different burn events at different sites, emphasizing the significant influence that the crop variety, prevailing weather conditions, and geographical location has on the type and number of pollutants emitted. The potential carcinogenicity of the PAH exposure was estimated based on toxic equivalency factors that showed varying risk potentials per burn event, with the highest value of 5.97 ng m-3 . Environ Toxicol Chem 2023;42:778-792. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

JWST-MIRI Synthetic Photometry Composition using 460 Spitzer-IRS Spectra of Nearby Galaxies

We use extragalactic Spitzer-InfraRed Spectrograph (IRS) spectroscopy to determine the polycyclic aromatic hydrocarbon band, emission line, and stellar and dust continuum contributions to the James Webb Space Telescope (JWST)-Mid-InfraRed Instrument (MIRI) photometric filters, F560W through F1280W, appropriate for z ∼ 0 star-forming galaxies. Our data set consists of 460 IRS-SL spectra from 5.25 to 14.8 μm. Of these, 340 are from large radial strips that sample a wide range of environments across three nearby galaxies. We also include 120 spectra from the Spitzer Infrared Nearby Galaxy Survey that are centered on the brightest star-forming regions in 46 nearby galaxies. This large compilation of extragalactic mid-infrared spectra facilitates the interpretation of future work with JWST-MIRI photometry of galaxies.

The stellar population responsible for a kiloparsec-size superbubble seen in the JWST ‘phantom’ images of NGC 628

ABSTRACT We here study the multiband properties of a kiloparsec-size superbubble in the late-type spiral galaxy NGC 628. The superbubble is the largest of many holes seen in the early release images using James Webb Space Telescope (JWST)/MIRI filters that trace the polycyclic aromatic hydrocarbon (PAH) emissions. The superbubble is located in the interarm region ∼3 kpc from the Galactic Centre in the south-east direction. The shell surrounding the superbubble is detected in H i, CO, and H α with an expansion velocity of 12 km s−1 and contains as much as 2 × 107 M⊙ of mass in gas that is mostly in molecular form. We find a clear excess of blue, bright stars inside the bubble as compared to the surrounding disc on the Hubble Space Telescope/Advanced Camera for Surveys images. These excess blue, bright stars are part of a stellar population of 105 M⊙ mass that is formed over the last 50 Myr in different star formation episodes, as determined from an analysis of colour–magnitude diagrams using a Bayesian technique. The mechanical power injected by the massive stars of these populations is sufficient to provide the energy necessary for the expansion of the shell gas. Slow and steady, rather than violent, injection of energy is probably the reason for the maintenance of the shell structure over the kiloparsec scale. The expanding shell is currently the site for triggered star formation as inferred from the JWST 21 µm (F2100W filter) and the H α images.

Single-pulse real-time billion-frames-per-second planar imaging of ultrafast nanoparticle-laser dynamics and temperature in flames

Unburnt hydrocarbon flames produce soot, which is the second biggest contributor to global warming and harmful to human health. The state-of-the-art high-speed imaging techniques, developed to study non-repeatable turbulent flames, are limited to million-frames-per-second imaging rates, falling short in capturing the dynamics of critical species. Unfortunately, these techniques do not provide a complete picture of flame-laser interactions, important for understanding soot formation. Furthermore, thermal effects induced by multiple consecutive pulses modify the optical properties of soot nanoparticles, thus making single-pulse imaging essential. Here, we report single-shot laser-sheet compressed ultrafast photography (LS-CUP) for billion-frames-per-second planar imaging of flame-laser dynamics. We observed laser-induced incandescence, elastic light scattering, and fluorescence of soot precursors - polycyclic aromatic hydrocarbons (PAHs) in real-time using a single nanosecond laser pulse. The spatiotemporal maps of the PAHs emission, soot temperature, primary nanoparticle size, soot aggregate size, and the number of monomers, present strong experimental evidence in support of the theory and modeling of soot inception and growth mechanism in flames. LS-CUP represents a generic and indispensable tool that combines a portfolio of ultrafast combustion diagnostic techniques, covering the entire lifecycle of soot nanoparticles, for probing extremely short-lived (picoseconds to nanoseconds) species in the spatiotemporal domain in non-repeatable turbulent environments. Finally, LS-CUP’s unparalleled capability of ultrafast wide-field temperature imaging in real-time is envisioned to unravel mysteries in modern physics such as hot plasma, sonoluminescence, and nuclear fusion.

Enhanced diesel emissions at low ambient temperature: hazardous materials in fine particles

The emission of fine particles (PM2.5) from diesel trucks is enhanced by low ambient temperatures, which is a fact that has attracted considerable attention. Carbonaceous matter and polycyclic aromatic hydrocarbons (PAHs) are the dominant hazardous materials in PM2.5. These materials induce severe adverse effects on air quality and human health and contribute to climate change. The emissions from heavy- and light-duty diesel trucks were tested at an ambient temperature of − 20 to − 13 ℃ and 18–24 ℃. This is the first study to quantify the enhanced carbonaceous matter and PAH emissions from diesel trucks at very low ambient temperatures based on an on-road emission test system. Features affecting diesel emissions, including driving speed, vehicle type, and engine certification level, were considered. The emissions of organic carbon, elemental carbon, and PAHs significantly increased from − 20 to − 13 ℃. The empirical results revealed that intensive abatement of diesel emissions at low ambient temperatures could benefit human health and have a positive influence on climate change. Considering the widespread applications worldwide, an investigation into diesel emissions of carbonaceous matter and PAHs in fine particles at low ambient temperatures is urgently required.

Spatiotemporal distribution, sources apportionment and ecological risks of PAHs: a study in the Wuhan section of the Yangtze River.

This study investigated the sources, contamination and ecological risks of polycyclic aromatic hydrocarbons (PAHs) based on their spatiotemporal distribution in aquatic environment in the Wuhan section of the Yangtze River (WYR). The fugacity ratio evaluation indicated that sediment was secondary release sources of two- and three-ring PAHs and sinks of four- and five-ring PAHs. The total concentrations of PAHs (Σ16PAHs) ranged from 2.51 to 102.5ng/L in water with the dominant contribution of 47.8% by two-ring PAHs. Σ16PAHs in sediments varied from 5.90 to 2926ng/g with the contribution of 35.4% by four-ring PAHs. The higher levels of PAHs occurred around developed industrial areas during the wet season, which was related to local industrial emissions and influenced by rainfall/runoff. Annual flux of Σ16PAHs was estimated of 28.77t. The PMF model analysis revealed that petroleum and industrial emissions were the dominant sources in water accounting for 58.5% of the total pollution, although traffic emission was the main source for sediment accounting for 44.6%. Risk assessments showed that PAHs in water were at low risks, whereas about 44% of the sediments were identified as medium risks. Therefore, energy structure adjustment and further implement of regulation and monitoring are necessary to reduce PAH emissions.