Production Of Polycyclic Aromatic Hydrocarbons Research Articles

Unraveling the impact of acrylonitrile on naphthyl radical during the growth process of polycyclic aromatic hydrocarbons

The introduction of ammonia effectively inhibits soot formation through its chemical interactions, partly attributable to the effects exerted by CN species. This study aims to investigate the influence of larger CN species, specifically acrylonitrile (C3H3N), identified in NH3-doped flames, on the growth process of polycyclic aromatic hydrocarbons (PAHs). The potential energy surfaces (PESs) governing the reaction between C3H3N and the naphthyl radical were explored utilizing G3(MP2, CC)//B3LYP/6-311G++(d,p) level theory. The formed C3H3N adducts exhibit the potential to generate PAHs featuring CH=CHCN side chain or nitrogen-containing PAHs (N-PAHs). The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was employed to calculate temperature- and pressure-dependent rate coefficients, enabling the assessment of yield distribution across the temperature range of 300–2500 K. In the 1-naphthyl + C3H3N reaction at 1 atm, the preferential formation of acenaphthylene-1-carbonitrile occurs at 300–1600 K, shifting towards PAHs with CH=CHCN side chains at temperatures exceeding 1600 K. The predominant production of PAHs with CH=CHCN side chains occurs in the 2-naphthyl + C3H3N reaction across all temperature ranges. These findings enhance our understanding of the mechanisms involving CN species and PAHs, significantly advancing the study of how intricate mechanisms influence PAH growth in NH3-doped flames.

Experimental and modeling study of fuel-rich oxidation of gasoline surrogate components/dimethyl carbonate blends in an atmospheric flow reactor

Fuel-rich oxidation of blending fuels consisting of three typical gasoline surrogate components (n-heptane, iso-octane, and toluene) and dimethyl carbonate (DMC) was investigated in an atmospheric-pressure flow reactor at mean gas temperatures from 1000 to 1350 K, equivalence ratio of 9.0, and residence time of 1.2 s. Blending ratios of DMC were 35 and 70 % on a molar basis. The mole fractions of not only polycyclic aromatic hydrocarbons (PAHs) up to 3 ring structure but also small intermediate species from C1 to C5 contained in sampled gas were experimentally quantified. A kinetic model that includes not only oxidation mechanism of gasoline surrogate components and DMC but also PAH growth reactions was developed to reproduce the experimental data. The experimental and simulated results showed that the blending effect of DMC on PAH production was different according to gasoline surrogate components. By blending DMC with n-heptane and iso-octane, the mole fractions of PAHs were generally reduced with an increase of the DMC blending ratio in the temperature range studied here. On the other hand, when DMC was blended with toluene, PAH production in the blending fuels was larger than that in pure toluene at a temperature below 1150 K, while the mole fractions of PAHs in pure toluene were identical to or larger than those in the blending fuels at a temperature above 1200 K. Because a reactivity of DMC is higher than toluene, toluene conversion was facilitated at a low temperature, leading to the promoted PAH production in the blending fuels compared to pure fuel. However, such a promoting effect of DMC was diminished at an elevated temperature, explaining the identical or large PAH production in neat toluene compared to the blending fuels. On the other hand, n-heptane and isooctane can be easily reacted even at a low temperature, suggesting that the promoting effect of DMC cannot be observed. This study reasonably succeeded in explaining the different DMC blending effects on PAH formation depending on the gasoline surrogate components. Novelty and significance statementExperiments and kinetic modeling for the mixtures consisting of dimethyl carbonate (DMC) and gasoline surrogate components, such as n-heptane, iso-octane, and toluene, were conducted to reveal the blending effect of DMC on polycyclic aromatic hydrocarbon (PAH) formation under the fuel-rich environment. It was found that DMC had a dilution effect in n-heptane/DMC and iso-octane/DMC blends, resulting in a reduction in PAH production with an increase of a DMC blending ratio. On the other hand, while DMC had the dilution effect in the toluene/DMC blend at an elevated temperature similar to other blends, toluene conversion was facilitated in the presence of DMC at a low temperature, resulting in the enhanced PAH production in the toluene/DMC blends compared to pure toluene.

Facile Synthesis of Nitrogen Cation-Doped Polycyclic Aromatic Hydrocarbons by Anodic Intramolecular Pyridination

The bottom-up synthesis of heteroatom-doped polycyclic aromatic hydrocarbons (PAHs) has attracted attention in the development of models of doped graphene. Among PAHs, nitrogen-cation (N +)-doped PAHs are known to exhibit superior optoelectronic functionalities; however, practical methods for synthesizing N +-doped PAHs are limited and challenging [1]. In our previous study, the SNAr reaction was used for the intramolecular cyclization of phenylpyridine derivatives possessing an electron-deficient perfluoroaryl moiety to give the corresponding N +-doped triphenylene in high yields under moderate conditions without the use of a transition-metal catalyst [2,3]. However, one of the challenges in the synthesis of N +-doped PAHs via the SNAr reaction is poor functional-group tolerance.Here, a facile and selective synthesis method for N +-doped PAHs has been established via anodic intramolecular cyclization, inspired by the Yoshida’s protocol for C–H amination without a transition-metal catalyst or an oxidant [4]. The reaction mechanism, in particular the reaction selectivity, was elucidated using density functional theory (DFT) calculations. The N +-doped PAH products were found to have a donor–acceptor structure composed of an arene moiety and a pyridinium moiety, as evidenced by DFT calculations, UV–vis analysis, and electrochemical measurements. The proposed intramolecular anodic pyridination is a practical strategy for the late-stage introduction of N+ into π-electron systems and broadens the scope of molecular design of N +-doped PAHs.

Critical review on the formations and exposure of polycyclic aromatic hydrocarbons (PAHs) in the conventional hydrocarbon-based fuels: Prevention and control strategies

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the atmosphere and primarily originate from the incomplete burning of fossil fuels and biofuels. Exposure to PAHs leads to harmful effects on human health and the environment. Diesel engines are a major source of PAH production in the transportation sector. Various approaches have been employed to reduce PAH emissions from diesel engines, including the use of biodiesel, green gaseous fuels, exhaust gas recirculation, exhaust after-treatment, and genetically modifying biodiesel with nanoparticles. This review focuses on PAH emissions from different generations of fuels and examines the remedial control actions taken to mitigate PAH formation. The study underscores the necessity for effective regulation of emissions from diesel engines, especially in developing countries where the reliance on fossil fuels is significant. Biodiesel has shown promise in reducing PAHs and carcinogenic pollutants, with higher biodiesel concentrations resulting in lower PAH formation. Replacing diesel with biodiesel and optimizing engine operating conditions are feasible methods to reduce PAH levels in the atmosphere. The use of nanoparticles in fuel blends and higher oxygen content in combustion chambers are also considered potential strategies for pollutant reduction. Additionally, the utilization of hydrogen and ammonia as secondary fuels has been explored as promising alternatives to fossil fuels. The study highlights the importance of further research on the presence of residual PAHs in the atmosphere and the implementation of strategies to curtail vehicular emissions.

Releasing and Assessing the Toxicity of Polycyclic Aromatic Hydrocarbons from Biochar Loaded with Iron.

Iron (Fe)-loaded biochar has garnered attention for its potential applications in recent years. However, the pyrolysis process of Fe-loaded biochar generates polycyclic aromatic hydrocarbons (PAHs), which can have adverse effects on both human health and the environment. This study explored the correlation between Fe loading and PAH production in Fe-loaded biochar. The results indicate that increasing Fe loading in biochar reduces the PAH concentration, with the most significant decrease observed in naphthalene (0.02-0.08 mg/kg). This reduction can be attributed to the decrease in precursor compounds (e.g., C2H2), substitution of the C=O bond by Fe-O, and a decrease in the dissolved organic matter concentration (3.19-10.76 mg/L) with Fe loading. When Fe loading increased from 0 to 10%, the ecological toxicity of biochar increased by 33.48% due to an elevated production of dibenzo[a,h]anthracene, which poses a significant risk to human health. Therefore, it is imperative to take into consideration the ecological risk of PAHs prior to the application of Fe-loaded biochar. This study presents a comprehensive risk assessment of Fe-loaded biochar and provides valuable insights into the optimization of its production and safe application.

The effect of polycyclic aromatic hydrocarbon biomarkers on cardiovascular diseases.

Polycyclic aromatic hydrocarbon (PAHs) are part of particulate matter (PM), which is produced from incomplete combustion of organic matter. Biomarkers mean biological indicators, molecules that indicate a normal or abnormal process in the body and may be a signof a condition or disease. Studies show that PAHs increase the risk of cardiovascular diseases through processes such as oxidative stress, inflammation andatherosclerosis. The present study focused on the evaluation of health effects PAHs biomarkers on cardiovascular diseases (CVD). In this narrative study, data werecollected from databases such as Scopus, PubMed, Web of science and Google Scholar in the period 1975-2023. After screening, duplicate and irrelevant articles were removed. Finally, 68 articles related to the effect of PAHs on CVD were included in the study. In addition to the articles found through the search in databases, another 18 articles from the references of the selected articles were included. According to the finding in during the biotransformation of PAH, a number of metabolites are made, such as phenols, diols, quinones, and epoxides. Phenolic isomers have the highest percentage and biomarkers used for their detection include 2-OHNAP used totrace naphthalene from heating processed food, 3-OHPHEN used to trace phenanthrene fromdiesel, 2-OHFLU used to trace fluorene and 1-OHPYR used to trace pyrene from cigarette and hookah smoke. According to the result, increasing blood pressure and heart rate and causing atherosclerosis are the main complications due to exposure to PAH metabolite on cardiovascular system. The most important agents that causes this affects including increased homocysteine, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), serum biomarkers of C-reactive protein, and triglycerides. Result this study showed that cardiovascular diseases riskis increased by exposure to PAH biomarkers from smoking, car emissions, occupational exposure, and incinerators. Therefore, strict controls should be implemented for sources of PAH production and exposure.

Comparison of PAHs behaviors in the pyrolysis products of oily sludge with different ash contents

Due to the presence of petroleum hydrocarbons, the production of polycyclic aromatic hydrocarbons (PAHs) is inevitable after oily sludge pyrolysis. The dispensation of PAHs in pyrolysis products was studied. The results indicated that PAHs were mainly enriched in liquid products, accounting for 97.97–99.88 %. Besides, the percentage of low-ring PAHs in products was the largest, subsequent to middle-ring PAHs. In the pyrolysis products of oily sludge with distinguishing ash contents, the impressions of pyrolysis temperature and residence time on the behaviors of PAHs were also compared. When pyrolysis temperature or residence time were variables, there were some similar characteristics in PAHs behaviors of oily sludge with different ash contents. The total concentration of PAHs in liquid products was positively correlated with pyrolysis temperature and residence time. The equal alteration was also exhibited in the concentration of high-ring PAHs in gas products with an increase in pyrolysis temperature. The formation of low-ring PAHs in liquid and gas products was improved by extended residence time. However, there were also differences in the evolution of PAHs in products of low-ash oily sludge (LOS) and high-ash oily sludge (HOS). The concentrations of low-ring and middle-ring PAHs in LOS gas products were positively correlated with pyrolysis temperature. Antithetically, the formation of low-ring and middle-ring PAHs in HOS gas products was inhibited by elevated pyrolysis temperature. Interestingly, the low-ring PAHs were converted into high-ring PAHs in HOS gas products with increasing pyrolysis temperature. As the residence time prolonged, the total concentrations of PAHs in LOS solid and gas products enlarged first and then reduced. Nevertheless, those of HOS were improved by continued residence time.

Probing PAH Formation from Heptane Pyrolysis in a Single-Pulse Shock Tube

ABSTRACT To improve our capabilities to model surrogate fuels, particularly in respect to polycyclic aromatic hydrocarbons (PAHs) and soot formation, the pyrolysis of n-heptane is studied in a single-pulse shock across a wide temperature range (900–1700 K) at 20 bar nominal pressure and 4 ms residence time. Three different initial fuel mole fractions are considered, 103, 502, and 2000 ppm of n-heptane in argon. Fuel and intermediate species, including aromatics up to three-ring structures, are measured using gas chromatography and mass spectrometry diagnostics. An ongoing detailed chemical kinetic model for PAH chemistry has been updated to successfully capture the fuel decomposition, the formation of small hydrocarbons, and the concentration of the main PAH products. Major reaction pathways to PAHs are highlighted as well as the role of important intermediate species.

Effect of curcumin on the formation of polycyclic aromatic hydrocarbons in grilled chicken wings

Organic macromolecules form carcinogenic and toxic substances such as polycyclic aromatic hydrocarbons (PAHs) under high temperature baking. Thus, this study investigated the effects and inhibition pathways of different curcumin concentrations (0.01, 0.05, 0.25, 0.3 mg/g) on seven PAHs in grilled chicken wings. The results demonstrated that curcumin concentrations displayed positive effects in inhibiting the formation of PAHs (16%–72%), increasing the total phenolic content (397.5–1934.4 mg/g) and free radical scavenging activity, and reducing TBARS values (31.15%–47.76%) and fatty acid content. Additionally, PCA and Pearson correlation analyses indicated that lipid oxidation (r = 0.42) and unsaturated fatty acids (r = 0.55) could promote the production of PAHs, while DPPH, ABTS and TPC could counteract their facilitation of PAHs. In conclusion, the addition of appropriate amounts of curcumin before grilling is a feasible strategy to reduce fat oxidation levels and the number of free radicals for the purpose of limiting PAHs content.

Upgrading and PAHs formation during used lubricant oil pyrolysis at different heating modes

Recycling used lubricant oil (ULO) to produce valuable products through pyrolysis is a flexible and efficient method. Presently, the mechanisms of oil conversion and polycyclic aromatic hydrocarbons (PAHs) formation during ULO pyrolysis at different thermal conditions were poorly explored. In this study, ULO pyrolysis at different heating modes (slow: 10 °C min−1, medium: ∼10,00 °C min−1, fast: >10000 °C min−1) were conducted at the temperature range of 400–700 °C. Extensive analyses on the chemical compositions and carbon number distributions of pyrolytic products were conducted to illustrate the mechanisms of ULO evolution and the formation of PAHs. Increasing temperature or heating rate can lead to more gas but less liquid production. The high temperature at fast heating mode can greatly promote the aromatization of pyrolytic oil. Various types of valuable products, such as base oil, fuel, and chemical feedstock, can be obtained at different heating rate conditions. More than 98% of PAHs produced from ULO pyrolysis were gathered in the liquid phase. Naphthalene, phenanthrene, and pyrene were the primary PAH species in both the liquid and gaseous products. Elevating the heating rate can lead to more PAH production and the enrichment of more toxic (5-/6-ring) PAHs in pyrolytic oil. Comparatively, distillation dominated in the slow pyrolysis, and chemical reactions of cracking and recombination occurred markedly at the medium and fast heating modes for both the ULO evolution and PAHs formation.

Formation of c-C6H5CN Ice Using the SPACE TIGER Experimental Setup

Benzonitrile (c-C6H5CN) has been recently detected in cold and dense regions of the interstellar medium, where it has been used as a signpost of a rich aromatic organic chemistry that might lead to the production of polycyclic aromatic hydrocarbons. One possible origin of this benzonitrile is interstellar ice chemistry involving benzene (c-C6H6) and nitrile molecules (organic molecules containing the −C≡N group). We have addressed the plausibility of this c-C6H5CN formation pathway through laboratory experiments using our new setup SPACE TIGER. The SPACE TIGER experimental setup is designed to explore the physics and chemistry of interstellar ice mantles using laser-based ice processing and product detection methods. We have found that c-C6H5CN is formed upon irradiation of c-C6H6:CH3CN binary ice mixtures with 2 keV electrons and Lyα photons at low temperatures (4−10 K). Formation of c-C6H5CN was also observed when c-C6H6 and CH3CN were embedded in a CO ice matrix, but it was efficiently quenched in a H2O ice matrix. The results presented in this work imply that interstellar ice chemistry involving benzene and nitrile molecules could contribute to the formation of the observed benzonitrile only if these species are present on top of the ice mantles or embedded in the CO-rich ice layer, instead of being mixed into the H2O-rich ice layer.

Blending effect of methanol on the formation of polycyclic aromatic hydrocarbons in the oxidation of toluene

Methanol has been considered as a potential renewable liquid fuel and blending it with gasoline and diesel is an effective way to reduce greenhouse gas emissions from the transport sector. To understand the mixing effect of methanol on the formation of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs), the fuel-rich oxidation of toluene with and without methanol was studied using a flow reactor at atmospheric pressure, temperatures from 1050 to 1350 K, equivalence ratio of 9.0, and residence time of 1.2 s. The blending ratio of methanol was varied as 0% and 50% on a molar basis. Gas chromatograph mass spectrometer was employed to identify and quantify PAHs and OPAHs in gaseous products. A kinetic model on PAH growth up to five ring structures was used to investigate the blending effect on PAH and OPAH formation. Both experiment and modeling showed that PAH and OPAH production at lower temperatures was unexpectedly promoted in toluene/methanol oxidation compared with toluene oxidation, while their production in toluene oxidation was identical with or larger than that in toluene/methanol oxidation at elevated temperatures. In methanol oxidation, no PAHs were produced under the current experimental conditions. Kinetic analysis indicated that high methanol reactivity produced several radicals, such as OH, H, and HO2, which promoted toluene reactivity at lower temperatures, resulting in the enlargement of PAH and OPAH formation in toluene/methanol oxidation compared to neat toluene oxidation. When the temperature was increased, the effect of methanol blending was diminished based on the kinetic analysis. These results suggest that oxygenated fuels do not necessarily reduce PAH production, but promote it under some conditions.

Incipient sooting tendency of oxygenated fuels doped in ethylene counterflow diffusion flames

The incipient sooting tendencies of oxygenated fuels in counterflow diffusion flames were systematically assessed by doping selected oxygenate fuels into the baseline fuel of ethylene with various mixing ratios. Laser light scattering and planar laser-induced fluorescence (PLIF) techniques were adopted. The critical oxygen mole fractions at different mixing ratios were identified with the use of laser scattering. It is found that the critical oxygen mole fraction varies with oxygenates, suggesting that the effect of mixing ethylene with oxygenates is highly sensitive to the types of oxygenate. While the doping of acetone moderately promoted the incipient sooting tendency, the doping of methanol, acetic acid, formic acid, and diethyl carbonate suppressed the formation of incipient soot. On the other hand, the doping of ethanol, dimethyl carbonate, diethyl ether, and dimethoxymethane had weak influences on the incipient sooting tendency. The production of polycyclic aromatic hydrocarbons (PAHs) of different sizes were measured by PLIF. The results show there was a strong correlation between the incipient sooting tendency and the production of large PAHs. One important finding is that, at their sooting limits, the total oxygen-to-carbon ratio of a stoichiometric fuel/oxygen mixture is linearly correlated with the mixing ratio of the ethylene-oxygenate mixture. This slope of these two quantities can be defined as an incipient sooting index (ISI) of oxygenated fuels for ranking their tendency of incipient sooting formation. Having the slopes correlated well with the oxygenates’ hydrogen/oxygen ratio, a reasonably accurate prediction of critical oxygen mole fractions from the molecule information of oxygenated fuels can be achieved.

Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame

Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.

Inherent and external factors influencing the distribution of PAHs, hydroxy-PAHs, carbonyl-PAHs and nitro-PAHs in urban road dust

The distribution and fate of hazardous polycyclic aromatic hydrocarbons (PAHs) and their associated transformed PAHs products (TPPs) notably carbonyl-PAHs (CPAHs), hydroxy-PAHs (HoPAHs), and nitro-PAHs (NPAHs) on urban road surfaces are influenced by diverse factors to varying extent. The pollutants are eventually transported to urban receiving waters via stormwater runoff posing risks to human and ecosystem health. In order to formulate an effective mitigation strategy, it is essential to comprehensively examine the role of both inherent and external factors in the distribution and fate of these hazardous pollutants, and thus, the need for this study. The research study showed that commercial land use has the highest cumulative concentration of PAHs and TPPs. Antecedent dry days (ADDs) has an inverse influence on the distribution of the total concentrations of low-molecular weight PAHs (LMW-PAHs), PAHs, and (PAHs + TPPs) irrespective of the type of land use, whilst there was no major influence on the total concentrations of high molecular weight PAHs (HMW-PAHs), and TPPs. The high volatility of LMW-PAHs compared to HMW-PAHs is considered to account for the decreasing concentration of LMW-PAH with increasing ADD. Particle size range has significant inverse influence on the cumulative concentration of pollutants across all land uses, since smaller particles are characteristically associated with larger surface area leading to the higher sorption of pollutants. Multivariate analysis of the influential factors indicated that two particle size ranges (0.45–150 μm and 150–425 μm) constitute the major influential factors on the distribution and fate of PAHs and TPPs in urban road dust. Greater quantum of pollutants are sorbed to the 0.45–150 μm particles due to the relatively higher specific surface area (SSA), concentration of total organic carbon (TOC) and total suspended solids (TSS) concentration. Therefore, it is critical to effectively remove finer particles from road surfaces in order to reduce exposure to hazardous pollutants.

Distribution, source and ecological risk assessment of polycyclic aromatic hydrocarbons in the sediments of northern part of the Persian Gulf

Distribution, sources, and ecological risk of 43 compounds of polycyclic aromatic hydrocarbons (PAHs) in surficial sediments of the Persian Gulf were investigated. The sediments were sampled from 60 offshore stations during an oceanographic cruise in the winter of 2012. Gas chromatography high-resolution mass spectrometry was used for the PAHs determinations in sediment samples. The concentrations of 21 parent PAHs, 7 methylated PAHs, 11 oxygenated PAHs and 4 nitrated PAHs were 9.0–201.5 ng g−1 dw, 3.3–60.3 ng g−1 dw, 15.2–172.7 ng g−1 dw and 0.1–8.3 ng g−1 dw, respectively. Among 21 parental PAHs, naphthalene (29.35 ng g−1 dw), phenanthrene (4.6 ng g−1 dw), and pyrene (3.18 ng g−1 dw) were the most abundant compound. 1-acenaphthenone (43.41 ng g−1 dw) and 2-methylnaphthalene (7.15 ng g−1 dw) showed the highest concentration in the oxy- and methyl-PAHs, respectively. The concentrations of nitro-PAHs were between not detected to 4 ng g−1 dw. According to the ecological risk assessment, the calculated total toxicity of PAHs was at below the lethal level on benthic organisms in all stations in the Persian Gulf, but there is risk of toxicity for the benthic organism in the Gulf of Oman (from the Strait of Hormuz to Jask). In general, nitrogenated and oxygenated derivatives did not show a significant risk in the study area. Based on the diagnostic ratios, the mixed sources (both petrogenic and pyrogenic) and pyrogenic sources have been identified for PAHs. Biomass combustion source has been identified for the stations near flares and gas fields. Principle component analysis-multivariate linear regression analysis for source identification shows that maritime traffic, abundant flares that burn the gas in oil, gas fields and dust storms have a major impact on the production of PAHs in this area.

PAH Growth in Flames and Space: Formation of the Phenalenyl Radical.

Polycyclic aromatic hydrocarbons (PAHs) are intermediates in the formation of soot particles and interstellar grains. However, their formation mechanisms in combustion and interstellar environments are not fully understood. The production of tricyclic PAHs and, in particular, the conversion of a PAH containing a five-membered ring to one with a six-membered ring are of interest to explain PAH abundances in combustion processes. In the present work, resonant ionization mass spectrometry in conjunction with isotopic labeling is used to investigate the formation of the phenalenyl radical from acenaphthylene and methane in an electrical discharge. We show that in this environment the CH cycloaddition mechanism converts a five-membered ring to a six-membered ring. This mechanism can occur in tandem with other PAH formation mechanisms such as hydrogen abstraction/acetylene addition (HACA) to produce larger PAHs in flames and the interstellar medium.

A Classification Model to Identify Direct-Acting Mutagenic Polycyclic Aromatic Hydrocarbon Transformation Products.

Polycyclic aromatic hydrocarbons (PAHs) are a complex group of environmental contaminants, many having long environmental half-lives. As these compounds degrade, the changes in their structure can result in a substantial increase in mutagenicity compared to the parent compound. Over time, each individual PAH can potentially degrade into several thousand unique transformation products, creating a complex, constantly evolving set of intermediates. Microbial degradation is the primary mechanism of their transformation and ultimate removal from the environment, and this process can result in mutagenic activation similar to the metabolic activation that can occur in multicellular organisms. The diversity of the potential intermediate structures in PAH-contaminated environments renders hazard assessment difficult for both remediation professionals and regulators. A mixture of structural and energetic descriptors has proven effective in existing studies for classifying which PAH transformation products will be mutagenic. However, most existing studies of environmental PAH mutagens primarily focus on nitrogenated derivatives, which are prevalent in the atmosphere and not as relevant in soil. Additionally, PAH products commonly found in the environment can range from as large as five rings to as small as a single ring, requiring a broadly inclusive methodology to comprehensively evaluate mutagenic potential. We developed a combination of supervised and unsupervised machine learning methods to predict environmentally induced PAH mutagenicity with improved performance over currently available tools. K-means clustering with principal component analysis allows us to identify molecular clusters that we hypothesize to have similar mechanisms of action. Recursive feature elimination identifies the most influential descriptors. The cluster-specific regression outperforms available classifiers in predicting direct-acting mutagens resulting from the microbial biodegradation of PAHs and provides direction for future studies evaluating the environmental hazards resulting from PAH biodegradation.

Importance of pyrolysis temperature and pressure in the concentration of polycyclic aromatic hydrocarbons in wood waste-derived biochars

Biochar addition to soil can lead to potential environmental risks due to its content of polycyclic aromatic hydrocarbons (PAHs). Until now, previous research focused on assessing the influence of pyrolysis peak temperature and feedstock on the formation and evolution of PAHs. Nevertheless, the effects of other important process parameters —such as pressure, gas residence time, and type of carrier gas— have not been comprehensively explored. To fill this gap, a 2-level full factorial design of experiments was conducted to assess the influence of the above-mentioned parameters on the pyrolysis behavior of an untreated wood waste as well as the properties of resulting biochars, including their PAHs contents. Results showed that the highest production of PAHs was reached at lower peak temperatures, whereas an increase in temperature led to a substantial reduction of the final PAHs content. An increased pressure also resulted in a marked decrease in PAHs, probably as a consequence of the higher carrier gas flow rates used under pressurized conditions, which could inhibit the generation of PAHs by condensation and polymerization. The outstanding results obtained from the phytotoxicity assessment for three plant species (barley, watercress, and basil) suggest that PAHs were not the major responsible for the observed short-term phytotoxic effects of biochars, since a considerable part of the phytotoxic compounds in biochar can be removed by a simple water washing step.

Five vs. six membered-ring PAH products from reaction of o-methylphenyl radical and two C3H4 isomers.

Gas-phase reactions of the o-methylphenyl (o-CH3C6H4) radical with the C3H4 isomers allene (H2C[double bond, length as m-dash]C[double bond, length as m-dash]CH2) and propyne (HC[triple bond, length as m-dash]C-CH3) are studied at 600 K and 4 Torr (533 Pa) using VUV synchrotron photoionisation mass spectrometry, quantum chemical calculations and RRKM modelling. Two major dissociation product ions arise following C3H4 addition: m/z 116 (CH3 loss) and 130 (H loss). These products correspond to small polycyclic aromatic hydrocarbons (PAHs). The m/z 116 signal for both reactions is conclusively assigned to indene (C9H8) and is the dominant product for the propyne reaction. Signal at m/z 130 for the propyne case is attributed to isomers of bicyclic methylindene (C10H10) + H, which contains a newly-formed methylated five-membered ring. The m/z 130 signal for allene, however, is dominated by the 1,2-dihydronaphthalene isomer arising from a newly created six-membered ring. Our results show that new ring formation from C3H4 addition to the methylphenyl radical requires an ortho-CH3 group - similar to o-methylphenyl radical oxidation. These reactions characteristically lead to bicyclic aromatic products, but the structure of the C3H4 co-reactant dictates the structure of the PAH product, with allene preferentially leading to the formation of two six-membered ring bicyclics and propyne resulting in the formation of six and five-membered bicyclic structures.