Speciation Profiles Research Articles

Speciation analysis of iodine in seaweed: optimisation of extraction procedure and chromatographic separation

Environmental context Seaweed is a good natural dietary source of iodine and some types of seaweed are rich in iodine. Iodine has a diverse chemistry in seaweeds and may exist as different chemical species; however, the occurrence and identity of the individual species are still not fully elucidated. Hence, development of sensitive and selective iodine speciation methods for studies of iodine chemistry and biotransformation in seaweeds are needed.Rationale Iodine is an essential element required for human health and metabolism. Seafood and especially seaweed can accumulate iodine to high amounts. Iodine may exist in different chemical forms (species) in seaweeds.Methodology The present study describes the development and optimisation of a method for iodine speciation analysis in seaweed based on high performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC-ICP-MS). The extraction procedure was conducted in two steps, pancreatic enzymatic extraction followed by alkaline extraction with tetramethylammonium hydroxide for optimum extraction efficiency without compromising species integrity.Results and discussion Total iodine and iodine species were determined in a range of brown (6 samples), red (6 samples) and green (3 samples) seaweeds. A large variation in the total iodine content of the different seaweeds was observed (33–5611 µg g–1 dry weight) with the highest levels encountered in brown seaweed. Iodine speciation analysis revealed differences in the speciation profile of the different types of seaweed. In all seaweeds iodide was the predominant species, and minor contents of MIT (monoiodotyrosine) and DIT (diiodotyrosine) were found in most seaweeds. Furthermore, peaks originating from six unknown iodine-containing species were observed in the chromatograms, especially in red and green seaweeds, while less abundant in brown seaweeds. The speciation method presented here will be valuable in future studies on iodine speciation in seaweed and an important tool for the investigation of iodine speciation and biotransformation in marine algae.

Bimolecular Peroxy Radical (RO2) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons

The kinetics of peroxy radical (RO2) reactions have been of long-standing interest in atmospheric and combustion chemistry. Nevertheless, the lack of kinetic studies at higher temperatures for their reactions with other radicals such as OH has precluded the inclusion of this class of reactions in detailed kinetics models developed for combustion applications. In this work, guided by the limited room-temperature experimental studies on selected alkyl-peroxy radicals and literature theoretical kinetics on the prototypical CH3O2 + OH system, we have performed parametric studies on the effect of uncertainties in the rate coefficients and branching ratios to potential product channels for RO2 + OH reactions at higher temperatures. Literature kinetics models were used to simulate autoignition delays, laminar flame speeds, and speciation profiles in flow and stirred reactors for a variety of common combustion-relevant fuels. Inclusion of RO2 + OH reactions was found to retard autoignition in fuel-lean (φ = 0.5) mixtures of ethane and dimethyl ether in air. The observed effects were noticeably more pronounced in ozone-enriched combustion of ethane and dimethyl ether. The simulations also examined the influence of ozone doping levels, pressures, and equivalence ratios for both ethane and dimethyl ether oxidation. Sensitivity and flux analyses revealed that the RO2 + OH reaction is a significant sink of RO2 radicals at the early stage of autoignition, affecting fuel oxidation through RO2 ↔ QOOH, RO2 ↔ alkene + HO2, or RO2 + HO2 ↔ ROOH + O2. Additionally, the kinetic stability of the trioxide formed from RO2 + OH reactions was investigated using master equation analyses. Last, we discuss other bimolecular reactions that are missing in literature kinetics models but are relevant to hydrocarbon oxidation initiated by external radical sources (plasma-enhanced, ozone-enriched combustion, etc.). The present simulations provide a strong motivation for better characterizing the bimolecular kinetics of peroxy radicals.

Host-Guest Chemistry in Discrete Polyoxo-12-Palladate(II) Cubes [MO8Pd12L8]n- (M = ScIII, CoII, CuII, L = AsO43-; M = CdII, HgII, L = PhAsO32-): Structure, Magnetism, and Catalytic Hydrogenation.

A family of five host-guest assemblies comprising different metal ions inside a cuboid 12-palladium-oxo cage, [MO8Pd12L8]n- (MPd12L8, M = ScIII, CoII, CuII, L = AsO43-; M = CdII, HgII, L = PhAsO32-), was synthesized and structurally characterized in the solid state by single-crystal X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis, and their solution and gas-phase stability were validated by multinuclear NMR spectroscopy and electrospray-ionization mass spectrometry (ESI-MS). The polyoxopalladates (POPs) ScPd12As8, CoPd12As8, and CuPd12As8 represent the first three examples of the MPd12As8 archetype. The unique cubic ligand field of {MO8} allows for collecting the speciation profiles of the POPs in solution using 45Sc and 113Cd NMR techniques. Detailed magnetic and electron paramagnetic resonance (EPR) studies were performed on CuPd12As8. Catalytic studies on MPd12As8 (M = CuII and CoII) supported on SBA-15 unveiled a guest metal-dependent structure-function relationship, with CuPd12As8 being the more efficient precatalyst for the hydroconversion of o-xylene in a fixed-bed reactor.

Reconciling the total carbon budget for boreal forest wildfire emissions using airborne observations

Abstract. Wildfire impacts on air quality and climate are expected to be exacerbated by climate change with the most pronounced impacts in the boreal biome. Despite the large geographic coverage, there is limited information on boreal forest wildfire emissions, particularly for organic compounds, which are critical inputs for air quality model predictions of downwind impacts. In this study, airborne measurements of 193 compounds from 15 instruments, including 173 non-methane organics compounds (NMOG), were used to provide the most detailed characterization, to date, of boreal forest wildfire emissions. Highly speciated measurements showed a large diversity of chemical classes highlighting the complexity of emissions. Using measurements of the total NMOG carbon (NMOGT), the ΣNMOG was found to be 50 % ± 3 % to 53 % ± 3 % of NMOGT, of which, the intermediate- and semi-volatile organic compounds (I/SVOCs) were estimated to account for 7 % to 10 %. These estimates of I/SVOC emission factors expand the volatility range of NMOG typically reported. Despite extensive speciation, a substantial portion of NMOGT remained unidentified (47 % ± 15 % to 50 % ± 15 %), with expected contributions from more highly-functionalized VOCs and I/SVOCs. The emission factors derived in this study improve wildfire chemical speciation profiles and are especially relevant for air quality modelling of boreal forest wildfires. These aircraft-derived emission estimates were further linked with those derived from satellite observations demonstrating their combined value in assessing variability in modelled emissions. These results contribute to the verification and improvement of models that are essential for reliable predictions of near-source and downwind pollution resulting from boreal forest wildfires.

Arsenic in groundwater of the Poyang Lake area (China): aqueous species and health risk assessment.

Arsenic is a pervasive pollutant in groundwater, affecting more than 100 million people in 50 countries, including China. Toxicological analysis of As is complicated because As exists in the environment in a variety of forms and redox states. Here, a thermodynamic equilibrium model was used to calculate As speciation, investigate pathways of As accumulation and assess the risk of adverse health effects from oral ingestion of dissolved As from shallow groundwater in the Poyang Lake area (China). The accumulation of As, Fe, and NH4+ in the studied shallow groundwater was found to be the result of the dissolution of As-containing Fe, and probably Mn, (oxyhydr)oxides under reducing conditions due to excess influx of organic matter into the shallow aquifer. Modeling showed that As(III), which is more toxic than As(V), predominated at nearly all sampling sites, regardless of redox conditions. Arsenic tends to accumulate in the highest concentrations as neutral species (As(OH)30, HAsO20) under Eh < 50mV. In the lower reaches of the Ganjiang and Xiushui Rivers, an increased non-carcinogenic risk from oral ingestion of As from drinking water was observed. The elevated cancer risk was found to be present throughout the study area. The lower reaches of the Ganjiang and Xiushui Rivers that have been shown to have the highest risk of both non-carcinogenic and carcinogenic adverse health effects are associated with more toxic As(III) species. Given the As speciation and risk profile, it is recommended to introduce strategies to alter redox conditions in shallow groundwater by adopting safer irrigation practices and managing fertilizer applicationsto avoid the buildup of high As concentrations associated with adverse health effects.

The speciation of arsenic in the muscle tissue of inland and coastal freshwater fish from a remote boreal region

Elevated concentrations of total arsenic (As) have been reported in boreal freshwater fish in both human-impacted and relatively pristine areas. We assessed the arsenic speciation profiles in muscle tissue of six fish species (n = 300) sampled from nine locations across a remote freshwater watershed in northern Ontario, Canada, extending from inland headwater lakes to the coastal marine confluence. Of the five arsenic species measured, only arsenobetaine (AsB) and dimethylarsinic acid (DMA) were detected in these fish. Riverine fish had up to 10-fold higher total [As] when compared to lacustrine fish. On average, these riverine fish also had higher percentages of AsB (%AsB, 60 ± 26%) and lower percentages of unmeasured arsenic (%UNM, 20 ± 21%), compared to lacustrine fish (28 ± 18% and 52 ± 21% %AsB and %UNM, respectively). DMA percentages (%DMA) were relatively consistent across the watershed, averaging 20 ± 21% across all fish. We examined ecological drivers of As speciation and found that %AsB increased slightly with fish weight in large-body predatory fish, but not in forage fish or insectivores. Furthermore, %AsB was positively related to trophic elevation (inferred from δ15N) in lacustrine fish across 3 out of 4 communities and within some populations. Lastly, riverine fish with a more marine-based diet had markedly higher %AsB when compared to fish with more freshwater-based diets, indicating an effect of anadromy on arsenic speciation. Overall, knowledge on arsenic speciation in freshwater fish has been limited and these results indicate potential drivers that can be considered in future studies. Furthermore, the absence of toxic inorganic As species in these boreal fish is an important consideration for future environmental monitoring practices and risk assessments, some of which assume 10–20% of total [As] in fish is present as toxic inorganic As. Additional studies on As bioaccumulation and biotransformation are needed in freshwater systems, particularly at the base of aquatic food webs.

Thermal decomposition of isopentanol: A theoretical calculation and kinetic modeling analysis

Isopentanol (3-methyl-1-butanol, 3M1B) is a prospective bioderived fuel with advantages over ethanol that make it a suitable substitute for gasoline. Although there have been studies on the combustion properties of 3M1B, reaction kinetics for its thermal decomposition is scarce. This study explores the reaction pathways for the thermal decomposition of 3M1B through theoretical calculations. Six reactions with tight transition states, and nine bond dissociation reactions (i.e., barrierless reactions) were considered. For reactions with tight transition states, the CCSD(T)/CBS//M06–2X-D3(0)/def2-TZVP method was used, and the MRCISD(+Q)/CBS//CASPT2/cc-pVDZ method was adopted for the bond dissociation reactions. The conventional transition state theory (CTST), including multi-structural torsional anharmonicity (MS-T) correction, addressed those reactions with tight transition states. The MS-T method thoroughly examined the co-effect of the multiple structures and torsional anharmonicity. Direct bond-breaking reactions were studied using the variational transition state theory (VTST). Subsequently, system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory and Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) were employed to obtain the rate constants for reactions with tight transition states and direct bond-breaking reactions at different temperatures and pressures (T/P) regimes (T = 298–2400 K, P = 0.01–100 atm), respectively. The results showed that water elimination and C-C bond dissociation play a significant role for 3M1B unimolecular decomposition, other molecular elimination and bond dissociation channels can be ignored. Combining the reaction pathways and the corresponding pressure dependent rate constants into the kinetic model resulted in good predictions of the speciation profiles during 3M1B pyrolysis. These data are valuable for the development of the combustion models of 3M1B.

Validation of Mercury Speciation Analysis in River Around Artisanal Small-Scale Gold Mining Area in West Nusa Tenggara, Indonesia

A method for determining mercury concentration using a mercury analyzer in a river water sample was validated according to ISO/IEC 17025. Analytical performance including linear range, limit of detection, precision and accuracy were evaluated. Mercury speciation profile was obtained from Pelangan River at three areas within Dusun Rambut Petung, an area with the highest amount of artisanal small-scale gold mining (ASGM) in Lombok, West Nusa Tenggara. Then, their concentration in each species was measured using sequential extraction. Good curve linearity was obtained in the concentration range of 0.1-5.0 µg/L and the limit of detection was 0.014 µg/L. The developed method has good precision and accuracy with a RSD value &lt;10% and a recovery of 94.16-101.91%. The detected fraction of mercury in the Pelangan river is organomercury, elemental mercury, and sulfide-bound species with each concentration of 0.732±0.032; 0.350±0.027; and 0.850±0.027 µg/L, respectively. The measurement results showed conformity with the reference method using CV-AAS. Therefore, this method can be applied to determine mercury levels in water for monitoring environmental quality.

Emission factors and chemical profile of I/SVOCs emitted from household biomass stove in China

Household combustion of biomass straw for cooking or heating is one of the most important emission sources of intermediate volatility and semi-volatile organic compounds (I/SVOCs). However, there are limited studies on the emission factors (EFs) and speciation profiles of I/SVOCs from household stoves burning biomass straw. In this study, experiments were conducted in a typical Chinese stove to test the EFs and species of I/SVOCs in three commonly used straws. It was revealed that EFs of I/SVOCs emitted from the burning of corn straw, rice straw, and wheat straw were 6.7, 1.9, and 9.8 g/kg, respectively, which accounted for 48.3 %, 36.8 %, and 48.6 % of total organic compounds emitted. Particulate organic compounds were dominated by ketones, oxygenated aromatics, acids, esters, and nitrogen-containing compounds, whereas the gaseous phase was dominated by aldehydes, acids, and aromatics. Although I/SVOCs only accounted for 18.1–23.6 % of the gaseous emissions from burning of straw, they represented 64.8–72.9 % of the secondary organic aerosol formation potential (SOAFP). The EFs of 16 priority polycyclic aromatic hydrocarbons (PAHs) were 362.0, 262.5, and 1145.2 mg/kg for corn straw, rice straw, and wheat straw, respectively, among which 3-ring and 4-ring PAHs were the main components. Thus, the results of this study provide new reliable I/SVOCs data that are useful for the development of an accurate emission inventory of organic compounds, simulation of secondary organic aerosol (SOA) formation, and health risk assessment.

Development and application of a supervised pattern recognition algorithm for identification of fuel-specific emissions profiles

Abstract. Wildfires have increased in frequency and intensity in the western United States (US) over the past decades, with negative consequences for air quality. Wildfires emit large quantities of particles and gases that serve as air pollutants and their precursors, and can lead to severe air quality conditions over large spatial and long temporal scales. Therefore, characterization of the chemical constituents in smoke as a function of combustion conditions, fuel type and fuel component is an important step towards improving the prediction of air quality effects from fires and evaluating mitigation strategies. Building on the comprehensive characterization of gaseous non-methane organic compounds (NMOCs) identified in laboratory and field studies, a supervised pattern recognition algorithm was developed that successfully identified unique chemical speciation profiles among similar fuel types common in western coniferous forests. The algorithm was developed using laboratory data from single fuel species and tested on simplified synthetic fuel mixtures. The fuel types in the synthetic mixtures were differentiated, but as the relative mixing proportions became more similar, the differentiation became poorer. Using the results from the pattern recognition algorithm, a classification model based on linear discriminant analysis was trained to differentiate smoke samples based on the contribution(s) of dominant fuel type(s). The classification model was applied to field data and, despite the complexity of the contributing fuels and the presence of fuels “unknown” to the classifier, the dominant sources/fuel types were identified. The pattern recognition and classification algorithms are a promising approach for identifying the types of fuels contributing to smoke samples and facilitating the selection of appropriate chemical speciation profiles for predictive air quality modeling using a highly reduced suite of measured NMOCs. The utility and performance of the pattern recognition and classification algorithms can be improved by expanding the training and test sets to include data from a broader range of single and mixed fuel types.

Experimental and theoretical study of the complexation of Fe3+ and Cu2+ by l‑ascorbic acid in aqueous solution

In this study, the ability of l-ascorbic acid to form complexes with Fe3+ and Cu2+ ions was investigated by using a combination of potentiometric measurements and DFT computations with the aim to recognize the coordination modes of the ligand and the most reliable complexes. Speciation profiles obtained by potentiometric titrations in aqueous solution (i.e., 0.16 M NaCl), and supported by UV–Vis data, show that a complexation occurs at 1:1 and 1:2 Fe(III)-to-ligand ratios and at 1:1, 1:2 and 1:3 Cu(II)-to-ligand ratios. The most plausible structures were firstly hypothesized by considering a general equilibrium that considers the effective ligands which enter in the coordination sphere of the metal ions: the anionic forms of ascorbic acid and hydroxide ion. Computational tools were, thus, exploited to ascertain the feasibility of the hypothesized complexes formation.

Toenail speciation biomarkers in arsenic‐related disease: a feasibility study for investigating the association between arsenic exposure and chronic disease

Long-term exposure to environmental arsenic has been associated with many chronic diseases, including several cancers, and diabetes. Urinary studies have implicated arsenic speciation as an important risk factor, however, such associations have not been replicated using toenail samples: a relatively new biosample for estimating long-term internal dose-exposure to arsenic. Despite having several advantages over conventional biosamples such as ease of collection and storage, standard methods for arsenic speciation analysis in toenails have not yet been established. The primary objectives of this study were to 1) establish an analytical method for arsenic speciation analysis in toenails, 2) describe preliminary arsenic speciation profiles of toenail samples from individuals with skin, lung, bladder, and kidney cancer, type II diabetes, and no known disease, and 3) determine if these speciation patterns differ between disease groups to inform the feasibility of subsequent research. A small cross-sectional feasibility study was carried out using 60 toenail samples and baseline questionnaire data from the Atlantic Partnership for Tomorrow’s Health (Atlantic PATH) study. Arsenic speciation profiles were determined using high performance liquid chromatography (HPLC) paired with inductively coupled plasma-mass spectrometry (ICP-MS). While no differences in total arsenic were found, arsenic speciation profiles were significantly different between certain cancer groups and the reference group with no known disease. Specifically, the percentage of monomethylarsonic acid (%MMA) was found to be significantly higher in the toenails of individuals with lung cancer and kidney cancer, compared to healthy individuals with similar total arsenic exposure. To the best of our knowledge, this is the first study to describe arsenic speciation patterns in individuals with several arsenic-related diseases using toenails: a convenient, non-invasive, biobankable sample capable of longer-term exposure estimation than conventional biosamples. These preliminary data provide evidence that toenail arsenic speciation patterns differ between groups with arsenic-related disease, and those with no known disease. Toenail arsenic speciation analysis is feasible and could potentially have important implications for research on arsenic-related diseases. Further investigation is warranted and would benefit from including detailed arsenic exposure data to explore the observed heterogeneity in arsenic speciation profiles.

Theoretical studies of real-fluid oxidation of hydrogen under supercritical conditions by using the virial equation of state

The Virial equation of state (EoS) was employed to describe the real-fluid impact on H2 oxidation simulation. Different from conventional empirical EoS methods fitted by using critical pressures and temperatures, such as Redlich-Kwong (RK) EoS, the Virial method was constructed with including intermolecular interactions, potentials, and molecular polarizations coupled with real-fluid partition function theory in this work. The Virial method was for the first time incorporated into Cantera software to realize real-fluid simulations with deeper-level physical insights. A series adiabatic/isothermal flow reactor and ignition delay simulations in H2O, N2, and CO2 diluents were performed. The calculations of species compressibility factors and thermodynamic properties by using the Virial method showed a better agreement with experimental data in literature than using the RK method. The Virial method also possessed a better performance in predicting experimental H2 ignition delay times and H2 speciation profiles from literatures. The effects of real fluid through corrections of compressibility factors, thermodynamic properties, and chemical potentials on supercritical H2 oxidation simulations in H2O diluents have been rigorously analyzed, respectively. Moreover, the Virial method performed well at adiabatic conditions in the bath gas of polar molecules like H2O, due to its consideration of molecular polarizations and higher accuracy of thermodynamic property calculations. We believed the Virial method could not only provide accurate estimations of real-fluid behavior, but also provided physical insights in the intermolecular interactions under supercritical conditions.

Experimental insights on the coordination modes of coumarin-3-carboxilic acid towards Cr(III)-, Co(II)-, Ni(II)-, Cu(II)- and Zn(II): A detailed potentiometric and spectroscopic investigation in aqueous media

Here complexation of coumarin-3-carboxilic acid (HCCA) with Cr(III), Co(II), Ni(II), Cu(II) and Zn(II) at 37 °C and in 0.16 M NaClO4 is discussed. Speciation profiles obtained by potentiometric titrations show that in aqueous solution a complexation occurs at a ligand-to-Cr(III), -Ni(II) and -Cu(II) ratio of 1:1, and at a ligand-to-Co(II) and -Zn(II) ratio of 1:1, 2:1 and 3:1. For Co(II)-HCCA system also a polynuclear species is formed (i.e., Co2(OH)(CCA)2+). The coordination sites of HCCA to the different metal ions were determined with the aid of UV–Vis, IR and X-ray diffraction. Solid state chemistry of HCCA was enriched of two new X-ray resolved structures for cobalt and nickel metal cations, which are also reported and discussed. From crystal packing analysis results the intricate motif of weak interactions that leads to a supramolecular interesting arrangement, not yet disclosed and argued in the previous literature about coumarin-3-carboxilic acid isostructural coordination compounds.

Aluminum(III), iron(III) and copper(II) complexes of luteolin: Stability, antioxidant, and anti-inflammatory properties

In this work complexation of luteolin (H4Lu) with Al(III), Fe(III) and Cu(II) at 37 °C and in 0.16 M NaCl is discussed. To evaluate the competition of the ligand for the metal cations and H+, the protonation constant of luteolin was also determined under the same experimental conditions. Speciation profiles obtained by potentiometric titrations show that in aqueous solution a complexation occurs at 1:1 ligand-to-Al(III) ratio, and at 1:1 and 2:1 ligand-to-cation ratios for Fe(III) and Cu(II). The coordination sites of luteolin to the different metal ions were determined by a computational approach, displaying that copper ion shows no selective preference towards any of the complexation sites of luteolin, while the six-membered chelate ring of the 4–5 site (i.e., the 4-carbonyl-5-hydroxyl site of the A and C rings of the ligand) is the preferred one for aluminum and iron ions. Additionally, we have evaluated the antioxidant and anti-inflammatory properties of free luteolin and of the luteolin-metal ion complexes. The complex with iron was found to have a higher activity than the other complexes (i.e., Fe(III)-Lu > Cu(II)-Lu > Al(III)-Lu), and its DPPH radical scavenging ability was even higher than that of free luteolin. Finally, all luteolin metal complexes were found to significantly reduce lipopolysaccharide (LPS)-induced interleukin (IL)-6 levels in monocyte-derived macrophages with the following order: Fe(III)-Lu > Al(III)-Lu > Cu(II)-Lu > free Lu.

The complex provenance of Cu-binding ligands in the South-East Atlantic

Organic ligands play a key role in the marine biogeochemical cycle of copper (Cu), a bio-essential element, regulating its solubility and bioavailability. However, the sources, abundance, and distribution of these ligands are still poorly understood. In this study, we examined vertical Cu speciation profiles from the South-East Atlantic (GEOTRACES section GA08). Profiles were collected from a range of ocean conditions, including the Benguela upwelling region, the oligotrophic South Atlantic Gyre, and the Congo River outflow. In general, the lack of a significant correlation between most of the parameters assessed here with Cu speciation data obscures the provenance of Cu-binding ligands, suggesting that Cu speciation in the South-East Atlantic is influenced by a complex interplay between biotic and abiotic processes. Nevertheless, the total dissolved Cu (CuT) illustrated an allochthonous origin in the working area, while Cu-binding ligands showed both an allochthonous and a biogenic, autochthonous origin. Pigment concentrations showed that the phylogeography of different microorganisms influenced the spatial features of the Cu-binding ligand pool in the South-East Atlantic. Allochthonous Cu-binding ligand sources in the upper water column are likely associated with dissolved organic matter which originated from the Congo River and the Benguela upwelling system. Deep water ligand sources could include refractory dissolved organic carbon (DOC), resuspended benthic inputs, and lateral advected inputs from the shelf margin. The degradation of L1-type ligands and/or siderophores in low oxygen conditions may also be a source of L2-type ligands in the deep. Free Cu ion levels (1.7 to 156 fM), the biologically available form of CuT, were below the putative biolimiting threshold of many marine organisms. Two classes of ligands were found in this study with total ligand concentrations ([LT]) ranging from 2.5 to 283.0 nM and conditional stability constants (logKCuL, Cu2+cond) ranging from 10.7 to 14.6. The Cu speciation values were spatially variable across the three subregions, suggesting that biogeochemical processes and sources strongly influence Cu speciation.

Ignition Delay Time and Oxidation of a Kerosene Aviation Fuel and a Blended Jet50-Bio50 Fuel.

Ignition delay and oxidation of two jet aviation fuels, Jet A-1 and its blended fuel with a bio-jet fuel in half, are investigated by experiments and numerical simulations. From their major combustion properties, derived cetane number and molecular weight of the blended fuel, Jet50-Bio50, are higher than those of Jet A-1, and its H/C ratio and threshold sooting index are lower because more n-alkanes are contained in a bio-jet fuel and aromatic compounds are not. The surrogate fuels of the two jet fuels are constructed for numerical simulations of their ignition and oxidation. Early ignition of the blended fuel measured in a shock tube experiment is investigated by comparing the speciation profiles of several products from the two fuels, and their global reactivity is measured in a laminar flow reactor. Oxidation of the blended fuel is initiated at a lower temperature than Jet A-1, and reaction pathways of the two fuels are analyzed at two temperatures of 600 and 1100 K, respectively. At a low temperature of 600 K, reaction pathways of the major surrogate components for the two fuels are significantly different, while they are almost the same at high temperatures. The active radical of OH is produced more by the oxidation of Jet50-Bio50, and its oxidation is initiated at a lower temperature than Jet A-1, leading to earlier ignition. At low temperatures, the difference between initiation times of oxidation of the two fuels is much larger than at high temperatures. At both temperatures, production rates of the major reaction steps, where OH is produced, are higher in Jet50-Bio50 than in Jet A-1.

Improved speciation profiles and estimation methodology for VOCs emissions: A case study in two chemical plants in eastern China

Volatile organic compounds (VOCs) poses a serious health risk through not only their own toxicity but also their role as precursors of ozone and secondary organic aerosols. The chemical industry, as one of the pillar industries in eastern China, is a key source of VOCs emissions. In this study, speciated VOCs emissions were measured in two chemical plants in eastern China. Oxygenated VOCs and aromatics were found to be the dominant species categories in both plants. The ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) of VOCs from dedicated resin production were both higher than general resin production. Three process-based models were used for the estimation of VOCs emissions from the two tested plants as a case study. The comparison between the emission factor model and the model with best available estimation methods (e.g., the measurement-based method, the mass balance method, the empirical formula method, and the correlation equation method) implied possible overestimation of the widely used emission factor model for the chemical industry. The probabilistic model developed in this study incorporated probability distribution of key parameters and proved to be a promising tool for emission inventory development and uncertainty analysis. The overall uncertainties of VOCs emissions based on the model were (−48%, +147%) and (−48%, +139%) for the two tested plants. In this study, the speciation profiles and estimation methodology for VOCs emissions from the chemical industry in China were both improved, which could benefit the accurate evaluation of the impacts of VOCs emissions.

Speciation and Antifungal Susceptiblity Profile of Candida Species –A Study from a Private Diagnostic Reference Lab in Mumbai

Speciation and Antifungal Susceptiblity Profile of Candida Species –A Study from a Private Diagnostic Reference Lab in Mumbai

Experimental and kinetic study on the pyrolysis and oxidation of isopentane in a jet-stirred reactor

An experimental and kinetic study on the pyrolysis and oxidation of isopentane (2-methylbutane) were conducted in this work. The experiments were performed in a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of oxygen, hydrogen, CO, CO2, C1C6 hydrocarbons and methanol were measured using a gas chromatograph (GC), at the initial fuel mole fraction of 0.5% and residence time at 2 s. Three literature kinetic models, named as the Bugler model, the NUIGMech1.1 model, and the LLNL model, were employed to predict the speciation profiles measured in this work, and the ignition delay times in the literature. Based on the model performances and kinetic analysis, some modifications were made to the LLNL model, by supplementing the beta-scission reaction aC5H11 = C4H8–1 +CH3, and updating the rate constants for the reactions iC5H12 + OH = cC5H11 + H2O, iC5H12 + OH = bC5H11 + H2O, C3H4-a = C3H4-p, C3H4-a + H = C3H4-p + H, and C2H6 + CH3 = C2H5 +CH4. After the modifications, the model predictions on mole fractions of 1-butene, ethane, allene and propyne in JSR pyrolysis and oxidation were improved, and the overestimations on the ignition delay times at low temperatures are significantly reduced. Reaction pathway and sensitivity analyses were carried out using the modified model. The results indicated that fuel consumption in pyrolysis is sensitive to the unimolecular decomposition reaction iC5H12 = iC3H7 + C2H5 across the temperature range of 900–1100 K. In addition, fuel low-temperature oxidation reactivity is sensitive to the mutual conversion between HO2 and H2O2, while the competition between OH and HO2 formation has a more pronounced effect at increased temperatures.