Fraction Of Polycyclic Aromatic Hydrocarbons Research Articles

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

A Multiwavelength Look at Galactic Massive Star-forming Regions

Abstract We present a multiwavelength study of 28 Galactic massive star-forming H ii regions. For 17 of these regions, we present new distance measurements based on Gaia DR2 parallaxes. By fitting a multicomponent dust, blackbody, and power-law continuum model to the 3.6 μm through 10 mm spectral energy distributions, we find that ∼34% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H ii regions, while ∼68% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H ii regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates N C ≥ 1050 s−1 and dust-processed L TIR ≥ 106.8 L ⊙) have on average higher percentages of absorbed Lyman continuum photons (∼51%) and reprocessed starlight (∼82%) compared to less luminous regions. Luminous H ii regions show lower average polycyclic aromatic hydrocarbon (PAH) fractions than less luminous regions, implying that the strong radiation fields from early-type massive stars are efficient at destroying PAH molecules. On average, the monochromatic luminosities at 8, 24, and 70 μm combined carry 94% of the dust-reprocessed L TIR. L 70 captures ∼52% of L TIR, and is therefore the preferred choice to infer the bolometric luminosity of dusty star-forming regions. We calibrate star formation rates (SFRs) based on L 24 and L 70 against the Lyman continuum photon rates of the massive stars in each region. Standard extragalactic calibrations of monochromatic SFRs based on population synthesis models are generally consistent with our values.

Effect of Tenax addition amount and desorption time on desorption behaviour for bioavailability prediction of polycyclic aromatic hydrocarbons

In this work, Tenax consecutive extractions of polycyclic aromatic hydrocarbons (PAHs) were conducted in two spiked sediments to investigate the influence of different Tenax addition amounts and desorption times on the rapidly desorbing fraction of PAHs, and to determine a reliable method for estimating PAHs bioavailability. The results indicated that a large Tenax addition amount has a positive effect on the desorption of PAHs from sediments. The desorption amounts of target PAHs compounds (3-ring phenanthrene and 4-ring fluoranthene) increased as the Tenax: sediment ratios increased from 0.25 to 2 in two spiked sediments. The highest desorption percentages of phenanthrene and fluoranthene were 48.91% and 34.70% for Jialing industrial park sediment, and 43.36% and 33.24% for Huanghuayuan bridge sediment, respectively. The results of desorption kinetics were suitably fitted with first order three-compartment model to estimate the rapidly desorbing fraction, Moreover, the Tenax: sediment ratio of 1 and desorption time of 24 h were found to be suitable for the desorption of phenanthrene and fluoranthene from sediments. The PAHs in sediments were biodegraded well by the bacterial strain J1-q. Comparing the maximum biodegraded amount of target PAHs in 30 days and the desorbed fraction over 400 h, the results showed that Tenax had better correlation with the high molecular weight fluoranthene than with the low molecular weight phenanthrene.

Wintertime air pollution and health risk assessment of inhalation exposure to polycyclic aromatic hydrocarbons in rural China

Household air pollution is one important environmental risk to human health in China, however, rural air pollution is often underappreciated and field measurements are limited compared to studies in urban area. The present study investigated indoor and outdoor polycyclic aromatic hydrocarbons (PAHs), and population inhalation exposure from two rural counties in Shanxi and Guizhou provinces, respectively. The indoor levels were higher than the corresponding outdoor concentration in both sites, which was mainly affected by the indoor fuel combustion emissions. A majority of particulate PAHs was found in submicron PM1.0. Fuel types had significant impacts on the total PAHs mass concentration but also composition profiles. In homes using electricity, the PAHs concentration was lower than those burning solid fuels, and there were relatively more fractions of low molecular weight PAHs with 2–3 rings, while for those burning solid fuels, higher fractions of high molecular weight PAHs with 5–6 rings may pose larger adverse health impacts. Although the daily inhalation exposure level for the population using electricity was much lower than those using solid fuels, the estimated Incremental Lifetime Cancer Risk still exceeded the deemed safe risk of 10−6. Inhalation exposure amounts measured by using portable carried samplers were compared to the estimation based on area concentration. The substantial discrepancy between them confirmed a preferable use of portable carried samplers in exposure evaluation and health risk assessment.

Novel in vitro method for measuring the mass fraction of bioaccessible atmospheric polycyclic aromatic hydrocarbons using simulated human lung fluids

The bioaccessibility of organic pollutants is a key factor in human health risk assessments. We developed a novel in vitro method for determining the mass fraction of bioaccessible atmospheric polycyclic aromatic hydrocarbons (PAHs) using an air-washing device containing simulated human lung fluid. The experimental parameters were optimized based on the deposition fractions (DFs) of PAHs in human lung fluids. The DFs were measured for PAHs based on the mass of compounds in the mainstream and exhaled cigarette smoke. The mass fractions of bioaccessible PAHs were measured by passing the mainstream cigarette smoke through the air-washing device, and they were calculated via a simple mass balance equation based on the PAHs in the fluid and mainstream cigarette smoke. The DFs of individual PAHs ranged from 20.5% to 78.1%, and the bioaccessible mass fractions varied between 45.5% and 99.8%. The octanol-water partition coefficients (KOW) significantly influenced both the DFs and bioaccessible mass fractions of PAHs, and the optimized in vitro method could be used to estimate the bioavailable atmospheric PAHs. This in vitro method can potentially be used to measure the mass fraction of bioaccessible atmospheric PAHs and to assess the health risk related to human exposure to airborne PAHs.

Effects of mixed surfactants on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in crops and the bioremediation of contaminated farmlands

Given the widespread contamination of polycyclic aromatic hydrocarbons (PAHs) in farmland, it is necessary to develop a technology to ensure the safety of agricultural productions and remediate the contaminated soils. In this study, a series of mixed surfactants were utilized to reduce the uptake of PAHs by crops in farming period and enhance the plant-microbe associated biodegradation in fallow period. During the farming period, the mixtures of cetyltrimethyl ammonium bromide (CTMAB) and Tween 80 were attached on soil by cationic-exchange and hydrogen bond, respectively, which increased soil organic matter to partition the bio-available fraction of PAHs. The maximum reduction of phenanthrene and pyrene was 88.6% and 94.9% for chrysanthemum (Chrysanthemum coronarium L.), and 90.6% and 91.9% for raphanus (Raphanus sativus L.), respectively. During the fallow period, sodium dodecyl benzene sulfonate (SDBS) reduced the adsorption loss of Tween 80 on soil to enhance desorption of PAHs. The mixtures of SDBS and Tween 80 increased the water-soluble fraction of PAHs in soils, modified bacterial community structure, and enriched the functional genes involved cell motility and signal transduction. Removal efficiencies of phenanthrene and pyrene in soils were high to 86.7% and 90.7%. This systematic technology provided an effective solution to remediate and plant on PAH-contaminated farmlands.

Enhanced biodegradation of sediment-bound heavily weathered crude oil with ligninolytic enzymes encapsulated in calcium-alginate beads

The degradation of crude and weathered crude oil following the application of crude and calcium-alginate encapsulated ligninolytic enzymes was studied using in situ microcosms. Changes in the chemical composition of the oil were monitored in crude enzyme extracts, as well as a sediment matrix, for as long as 70 days. Compound-specific effects of ligninolytic enzymes applied to the sediments were observed over time through changes in concentration of total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs) and fractions of saturates, aromatics, resins and asphaltenes (SARA). As the oil weathered, most TPH and PAH fractions showed a rapid decrease in concentration. As sediment oil concentrations decreased following treatment with ligninolytic enzymes, the microbial population was enriched with hydrocarbon-degrading species. This trend demonstrates that the oil fractions initially not bioavailable for microbial degradation, were subsequently released to the sediment via catalytic conversion with laccase and manganese peroxidase, and the oil continues to be biodegraded by microbial populations.

Gas-particle partitioning and health risk estimation of polycyclic aromatic hydrocarbons (PAHs) at urban, suburban and tunnel atmospheres: Use of measured EC and OC in model calculations

Gas and particle phase ambient concentrations polycyclic aromatic hydrocarbons (∑13PAH) were determined at urban and suburban sites in Eskişehir and in a traffic-tunnel. Organic and elemental carbon (OC and EC) concentrations of total suspended particles (TSP) were also measured. Atmospheric ∑13PAH (gas+particle) concentrations measured at suburban sites was found to be lower than that of tunnel and urban site. Concentrations of TSP and OC/EC were highest in the tunnel. Fluorene, Phe, Flt and Pyr were the most dominant PAH compounds in gas phase samples for all three sampling locations, while BaA, Chr, BbF, BkF and BaP were found to be higher in particle phase. Gas-particle partitioning coefficients, (Kp) and particle-phase fractions (Φ) of PAHs were correlated with supercooled vapor pressures ( P L o ). Non-linear curve fitting of Φ versus log P L o was found to be more robust than linear logarithmic regressions of log Kp versus log P L o . Kp of PAHs were estimated by octanol-air and soot-air partitioning models and the results were compared with the experimental Kp values. Measured EC and OC concentrations were used in model calculations. Use of measured carbon concentrations in model calculations resulted much better estimations for tunnel samples. Gas-particle partitioning of PAHs for the majority of the compounds were controlled by adsorption onto soot carbon and adsorption into the organic matter. Cancer risks associated with inhalation and dermal contact were also estimated. Generally, the estimated cancer risks were below 1 × 10 −5 for urban and suburban sampling locations. • PAHs, OC and EC concentrations were determined in urban, suburban and tunnel atmospheres. • Gas-particle distribution of PAHs were investigated by linear and non-linear modeling approaches. • Gas-particle partitioning of PAHs mainly controlled by adsorption onto soot carbon and adsorption into the organic matter. • Cancer risks associated with inhalation and dermal contact were also estimated.

Assessing Biodegradation Susceptibilities of Selected Petroleum Hydrocarbons at Contaminated Soils

Assessing Biodegradation Susceptibilities of Selected Petroleum Hydrocarbons at Contaminated Soils (M.H. Langsa): The susceptibility to biodegradation of selected saturated hydrocarbons (SHCs), polycyclic aromatic hydrocarbons (PAHs) and asphaltenes in a Barrow crude oil and extracts isolated from soils contaminated with the Barrow crude oil at day 0 and 39 was determined. Soil samples were contaminated with a Barrow crude oil across the surface (5% w/w) as part of a mesocosm experiment in order to mimic similar conditions in the environment. The extent of biodegradation of the Barrow oil extracted from the contaminated soils at day 0 and day 39 was assessed by GC-MS analyses of SHCs and PAHs fractions. Changes in the relative abundances of n-alkanes (loss of low-molecular-weight hydrocarbons) and pristane relative to phytane (Pr/Ph) and their diastereoisomers were determined. Changes in the diastereo-isomer ratios of Pr and Ph relate to the decrease in abundance of the phytol-derived 6(R),10(S) isoprenoids with increasing biodegradation. The percentage change in abundances of each of selected alkylnaphathalenes with time (day 0 to 39) was determined, enabling an order of susceptibility of their isomers to biodegradation. It was established that the 2-methylnaphthalene isomers (2-MN) is more susceptible to microbial attack than 1-MN isomer indicated by decreasing in percent abundance from day 0 to 39 for the 2-MN isomer. The GC-MS analyses of the original Barrow oil indicated the oil had not undergone biodegradation. When this oil was used in the soil mesocosm experiments the oil was shown to biodegrade to about a level 2 -3 based on the biodegradation susceptibility of the various SHCs and PAHs described above.

Emission characteristics for gaseous- and size-segregated particulate PAHs in coal combustion flue gas from circulating fluidized bed (CFB) boiler

The partitioning behavior of polycyclic aromatic hydrocarbons (PAHs) between gaseous and particulate phases from coal-fired power plants (CFPPs) is critically important to predict PAH removal by dust control devices. In this study, 16 US-EPA priority PAHs in gaseous and size-segregated particulate phases at the inlet and outlet of the fabric filter unit (FFs) of a circulating fluidized bed (CFB) boiler were analyzed. The partitioning mechanisms of PAHs between gaseous and particulate phases and in particles of different size classes were investigated. We found that the removal efficiencies of PAHs are 45.59% and 70.67–89.06% for gaseous and particulate phases, respectively. The gaseous phase mainly contains low molecular weight (LMW) PAHs (2- and 3-ring PAHs), which is quite different from the particulate phase that mainly contains medium and high molecular weight (MMW and HMW) PAHs (4- to 6-ring PAHs). The fractions of LMW PAHs show a declining trend with the decrease of particle size. The gas-particle partitioning of PAHs is primarily controlled by organic carbon absorption, in addition, it has a clear dependence on the particle sizes. Plot of log (TPAH/PM) against logDp shows that all slope values were below −1, suggesting that PAHs were mainly adsorbed to particulates. The adsorption effect of PAHs in size-segregated PMs for HMW PAHs is more evident than LMW PAHs. The particle size distributions (PSDs) of individual PAHs show that most of PAHs exhibit bi-model structures, with one mode peaking in the accumulation size range (2.1–1.1 μm) and another mode peaking in coarse size range (5.8–4.7 μm). The intensities of these two peaks vary in function of ring number of PAHs, which is likely attributed to Kelvin effect that the less volatile HMW PAH species preferentially condense onto the finer particulates. The emission factor of PAHs was calculated as 3.53 mg/kg of coal burned, with overall mean EFPAH of 0.55 and 2.98 mg/kg for gaseous and particulate phase, respectively. Moreover, the average emission amount of PAHs for the investigated CFPP was 1016.6 g/day and 371073.6 g/y, respectively.

Effect of industrial microwave irradiation on the physicochemical properties and pyrolysis characteristics of lignite

Abstract The surface functional groups and pyrolysis characteristics of lignite irradiated by microwave were comparatively studied to evaluate the feasibility of using industrial 915 MHz for lignite drying. The drying kinetics, micro structure, chemical functional groups, re-adsorption properties, and pyrolysis characteristics of the dried coal were respectively analyzed. Results indicated that for typical Chinese lignite studied in this paper, 915 MHz microwave drying was 7.8 times faster than that of the hot air drying. After industrial microwave drying, the sample possessed much higher total specific surface area and specific pore volume than that of air dried sample. The oxygen functional groups and re-adsorption ratio of microwave irradiated coal decreased, showing weakened hydrophilicity. Moreover, during the pyrolysis of the coal dried by hot air and microwave, the yield of tar largely increased from 1.3% to 8.5% and the gas production increased correspondingly. The composition of the tar was also furtherly analyzed, results indicated that Miscellaneous hydrocarbons (HCs) were the main component of the tar, and microwave irradiation can reduce the fraction of polycyclic aromatic hydrocarbons (PAHs) from 26.4% to 22.7%.

Multidimensional Gas Chromatography–Mass Spectrometry Method for Fingerprinting Polycyclic Aromatic Hydrocarbons and Their Alkyl-Homologs in Crude Oil

ABSTRACTThe composition of polycyclic aromatic hydrocarbons in crude oil is usually too complex to use standard capillary gas chromatography to separate all of the components. In this study, a multidimensional gas chromatography–mass spectrometry (GC-MS) technique was used to analyze polycyclic aromatic hydrocarbon fractions of crude oil collected from the Dongying oil field in the Bohai Sea. A DB-17MS column (30 m × 0.25 mm × 0.25 µm) was used as a prefractionating column and only selected heart-cuts were transferred to the second chromatographic dimension (HP-5MS, 15 m × 0.25 mm × 0.25 µm) by a pressure-adjusted continual flow-type switching device for quantification of the polycyclic aromatic hydrocarbons. The chromatographic elements and parameters, such as detector selection and column combinations, were optimized. Naphthalene, phenanthrene, fluorene, dibenzothiophene, chrysene, and their C1–C4 alkyl homologs were identified. The profile of the polycyclic aromatic hydrocarbons obtained using the multidimensional GC-MS method was compared with the results obtained by traditional one-dimensional GC-MS.

Assessment of Polycyclic Aromatic Hydrocarbons in School Playground Soils in Urban Gwangju, South Korea

Soil samples from school playground of Gwangju City were analyzed for 16 polycyclic aromatic hydrocarbons (PAHs), and the soil contamination status and the potential cancer risk for students and adults were investigated. Soil samples were collected from 57 sites from 5 districts of Gwangju City in the summer of 2013. Regardless of the sampling site, the ∑PAHs concentrations ranged from 13.2 to 145.5ng/g (mean 51.2ng/g). Four and five-ring PAHs were predominant in the soil samples while the fraction of two-ring PAHs was the lowest. Seven carcinogenic PAHs contributed ~55% of ∑PAHs in school playground soils. The benzo[a]pyrene (46.4%) and dibenz[a,h]anthracene (41.2%) were the major contributors to toxic equivalent quantity. The strong correlation between carcinogenic PAHs suggested that they originated from the same source either vehicular emission or coal combustion, because they are markers of these pollution sources. The mean cancer risk for students (3.61×10-7) and adults (8.41×10-6) was in the U.S. EPA safety range (<10-6).

Regional modelling of polycyclic aromatic hydrocarbons: WRF-Chem-PAH model development and East Asia case studies

Abstract. Polycyclic aromatic hydrocarbons (PAHs) are hazardous pollutants, with increasing emissions in pace with economic development in East Asia, but their distribution and fate in the atmosphere are not yet well understood. We extended the regional atmospheric chemistry model WRF-Chem (Weather Research Forecast model with Chemistry module) to comprehensively study the atmospheric distribution and the fate of low-concentration, slowly degrading semivolatile compounds. The WRF-Chem-PAH model reflects the state-of-the-art understanding of current PAHs studies with several new or updated features. It was applied for PAHs covering a wide range of volatility and hydrophobicity, i.e. phenanthrene, chrysene and benzo[a]pyrene, in East Asia. Temporally highly resolved PAH concentrations and particulate mass fractions were evaluated against observations. The WRF-Chem-PAH model is able to reasonably well simulate the concentration levels and particulate mass fractions of PAHs near the sources and at a remote outflow region of East Asia, in high spatial and temporal resolutions. Sensitivity study shows that the heterogeneous reaction with ozone and the homogeneous reaction with the nitrate radical significantly influence the fate and distributions of PAHs. The methods to implement new species and to correct the transport problems can be applied to other newly implemented species in WRF-Chem.

Polycyclic Aromatic Hydrocarbons in Soil Organic Horizons Depending on the Soil Burn Severity and Type of Ecosystem

AbstractBecause forest fires are a source of polycyclic aromatic hydrocarbons (PAHs), the influence of burnt conditions is of paramount importance and has not been thoroughly studied yet. In this study, two types of forest stands (Pinus nigra and Pinus pinaster) and two shrubland systems (Erica arborea and Ulex europaeus), differing in litter properties (composition and flammability), were considered. Changes in PAH levels were analysed in unburnt and charred litter, and they were related to different levels of soil burn severity and the organic matter composition of the charred litter, including charcoal and/or ashes. For monitoring PAH levels, an analytical method to determine them in unburnt and burnt woodland samples by pressure liquid extraction using a solid phase extraction cleanup was optimized. The highest levels of PAHs were found in the charred litter of P. pinaster (especially at soil burn severity = 200–400 °C), followed by U. europaeus, which presented similar concentration than Erica arborea and, finally, P. nigra. An association between the low molecular weight PAHs and 50% burn‐off temperature differential scanning calorimetry supports the idea of fire smoke as the main source of low molecular weight PAHs in charred biomass generated at temperatures of 200–400 °C. Instead, the fraction of high molecular weight PAHs is related to hydrogen‐to‐carbon and oxygen‐to‐carbon ash‐free dry weight, with charring depending on their organic matter content in the burnt material. PAH mobility will depend on the solubility of the organic matter, which is higher at higher pHs. The higher risk is the transport downstream to rivers or wet systems. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Mangrove Oyster (Crassostrea belcheri) as a Biomonitor Species for Bioavailability of Polycyclic Aromatic Hydrocarbons (PAHs) from Sediment of the West Coast of Peninsular Malaysia

ABSTRACTRapid industrialization and urbanization in the west coast of Peninsular Malaysia has caused increasing pollution particularly of petroleum and petroleum by-products. Surface sediment and mangrove oyster (Crassostrea belcheri) were collected from five mangrove ecosystems in the west coast of Peninsular Malaysia and investigated for bioavailability of polycyclic aromatic hydrocarbons (PAHs). Sampling locations were selected from both remote areas with few or no previous records of petroleum pollution such as Pulau Merambong and polluted areas that are under international attention such as Klang mangrove ecosystem. PAH fractions were obtained through soxhlet extraction and two-step column chromatography and the fractions were injected to gas chromatography-mass spectrometry (GC-MS) for analysis. The concentrations of PAHs ranged from 151 to 4973 ng g−1 dw in the sediments, while from 309 to 2225 ng g−1 dw in the oysters. When tested for diagnostic ratios, a predominance of pyrogenic source PAHs was detected in the sediments, whereas PAHs in the oysters had mixed petrogenic and pyrogenic sources. A significant correlation (p < 0.05) was found between high molecular weight (HMW) PAHs in the sediments and oysters and biota accumulation factors (BAFs) of PAHs were approaching or exceeding unity indicating the ability of mangrove oyster in bioaccumulation of PAHs. Overall, this study indicates that mangrove oyster (C. belcheri) can be used as a biomonitor species for PAHs in an aquatic environment.

Cytotoxicity of Biochar: A Workplace Safety Concern?

Biochar has a number of environmental applications, including soil amendment for agriculture, remediation of contaminated soils and sediments, and climate change mitigation. Dust formed during its production and field application may pose a health risk, but the cytotoxicity of biochar has, to the best of our knowledge, not previously been investigated. Therefore, we measured the concentration-dependent cytotoxicity of biochar on an NIH 3T3 mouse fibroblast cell line. We used a contaminant trap experiment to measure the total and nondesorbable polycyclic aromatic hydrocarbon (PAH) fractions of the biochar. PAH release was found to be negligible because of the biochar’s strong PAH sorption potential. The biochar was nevertheless observed to have a cytotoxic effect on the fibroblast cells; the EC10 values were 49.6 and 18.8 μg/mL after incubation for 24 and 48 h, respectively. This cytotoxic effect is likely to relate to the particulate nature and size distribution of the biochar; the biochar had particles s...

Relation between the parameters of dust and of molecular and atomic gas in extragalactic star-forming regions

The relationships between atomic and molecular hydrogen and dust of various sizes in extragalactic star-forming regions are considered, based on observational data from the Spitzer and Herschel infrared space telescopes, the Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source sample consists of approximately 300 star-forming regions in 11 nearby galaxies. Aperture photometry has been applied to measure the fluxes in eight infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160$\mu$m), the atomic hydrogen (21cm) line and CO (2--1) lines. The parameters of the dust in the starforming regions were determined via synthetic-spectra fitting, such as the total dust mass, the fraction of polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes with the measured parameters shows that the relationships between atomic hydrogen, molecular hydrogen, and dust are different in low- and high-metallicity regions. Low-metallicity regions contain more atomic gas, but less molecular gas and dust, including PAHs. The mass of dust constitutes about $1\%$ of the mass of molecular gas in all regions considered. Fluxes produced by atomic and molecular gas do not correlate with the parameters of the stellar radiation, whereas the dust fluxes grow with increasing mean intensity of stellar radiation and the fraction of enhanced stellar radiation. The ratio of the fluxes at 8 and 24$\mu$m, which characterizes the PAH content, decreases with increasing intensity of the stellar radiation, possibly indicating evolutionary variations of the PAH content. The results confirm that the contribution of the 24$\mu$m emission to the total IR luminosity of extragalactic star-forming regions does not depend on the metallicity.

Enhanced Accessibility of Polycyclic Aromatic Hydrocarbons (PAHs) and Heterocyclic PAHs in Industrially Contaminated Soil after Passive Dosing of a Competitive Sorbate.

To assess the exposure to polycyclic aromatic hydrocarbons (PAHs) it is important to understand the binding mechanisms between specific soil constituents and the organic pollutant. In this study, sorptive bioaccessibility extraction (SBE) was applied to quantify the accessible PAH fraction in industrially contaminated soil with and without passive dosing of a competitive sorbate. SBE experiments revealed an accessible PAH fraction of 41 ± 1% (∑16 US EPA PAHs + 5 further PAHs). The passive dosing of toluene below its saturation level revealed competitive binding and resulted in an average increase of the accessible fraction to 49 ± 2%, whereby primarily the accessibility of higher molecular weight PAHs (log Kow > 6) was affected. Competitive binding was verified using the same soil with only desorption-resistant PAHs present. In this experiment, passive dosing of toluene resulted in desorption of 13 ± 0.4% PAH. We explain increased PAH desorption after addition of toluene by competitive adsorption to high-affinity sorption sites while acknowledging that toluene could additionally have increased PAH mobility within the soil matrix. Findings suggest that the presence of copollutants at contaminated sites deserves specific considerations as these may increase accessibility and thereby exposure and mobility of PAHs.

Comparative study of the soot formation process in a “nucleation” and a “sooting” low pressure premixed methane flame

The soot formation process was investigated in two low pressure premixed methane flames: a reference sooting flame with equivalence ratio 2.32 and a so called nucleation flame with equivalence ratio 1.95. In the nucleation flame no measureable soot growth after soot inception occurs, and the soot mass increases only by nucleation from the gas phase.Several experimental techniques were used to gain insights on the soot formation and growth processes, including (1) in situ laser induced incandescence (LII) to measure the soot volume fraction and the primary particle size, (2) online jet cooled laser induced fluorescence (JCLIF) to measure the mole fraction of pyrene and fluoranthene and (3) ex-situ secondary ion mass spectrometry (ToF-SIMS) to investigate the chemical composition of the gas phase. Particular attention is devoted to soot gaseous precursors like polycyclic aromatic hydrocarbons (PAHs).ToF-SIMS analyses provide evidences that large hydrocarbons are formed in both flames via hydrogen abstraction/acetylene addition (HACA) mechanism. However, significant differences in the soot volume fraction and concentration profiles of PAHs are observed in the nucleation flame with respect to the reference sooting flame. In particular, in the nucleation flame the average soot particle diameter and the concentration of the larger measured gaseous soot precursors show weak variation all along the flame reaction coordinate. Kinetic modeling was used to help understanding this steady state behavior which is well reproduced in simulations and is found to be related to nearly balanced soot mass growth and loss phenomena currently modeled only by acetylene addition and soot oxidation.