Speciation Information Research Articles

The speciation of marine particulate iron adjacent to active and passive continental margins

We use synchrotron-based chemical-species mapping techniques to compare the speciation of suspended (1–51μm) marine particulate iron collected in two open ocean environments adjacent to active and passive continental margins. Chemical-species mapping provides speciation information for heterogeneous environmental samples, and is especially good for detecting spectroscopically distinct trace minerals and species that could not be detectable by other methods. The average oxidation state of marine particulate iron determined by chemical-species mapping is comparable to that determined by standard bulk X-ray Absorption Near Edge Structure spectroscopy. Using chemical-species mapping, we find that up to 43% of particulate Fe in the Northwest Pacific at the depth of the adjacent active continental margin is in the Fe(II) state, with the balance Fe(III). In contrast, particulate iron in the eastern tropical North Atlantic, which receives the highest dust deposition on Earth and is adjacent to a passive margin, is dominated by weathered and oxidized Fe compounds, with Fe(III) contributing 90% of total iron. The balance is composed primarily of Fe(II)-containing species, but we detected individual pyrite particles in some samples within an oxygen minimum zone in the upper thermocline. Several lines of evidence point to the adjacent Mauritanian continental shelf as the source of pyrite to the water column. The speciation of suspended marine particulate iron reflects the mineralogy of iron from the adjacent continental margins. Since the solubility of particulate iron has been shown to be a function of its speciation, this may have implications for the bioavailability of particulate iron adjacent to passive compared to active continental margins.

Accuracy and Precision of Species Trees: Effects of Locus, Individual, and Base Pair Sampling on Inference of Species Trees in Lizards of the Liolaemus darwinii Group (Squamata, Liolaemidae)

Molecular phylogenetics has entered a new era in which species trees are estimated from a collection of gene trees using methods that accommodate their heterogeneity and discordance with the species tree. Empirical evaluation of species trees is necessary to assess the performance (i.e., accuracy and precision) of these methods with real data, which consists of gene genealogies likely shaped by different historical and demographic processes. We analyzed 20 loci for 16 species of the South American lizards of the Liolaemus darwinii species group and reconstructed a species tree with *BEAST, then compared the performance of this method under different sampling strategies of loci, individuals, and sequence lengths. We found an increase in the accuracy and precision of species trees with the number of loci, but for any number of loci, accuracy substantially decreased only when using only one individual per species or 25% of the full sequence length (∼ 147 bp). In addition, locus "informativeness" was an important factor in the accuracy/precision of species trees when using a few loci, but it became increasingly irrelevant with additional loci. Our empirical results combined with the previous simulation studies suggest that there is an optimal range of sampling effort of loci, individuals, and sequence lengths for a given speciation history and information content of the data. Future studies should be directed toward further assessment of other factors that can impact performance of species trees, including gene flow, locus "informativeness," tree shape, missing data, and errors in species delimitation.

Testing of alternative hypotheses for speciation: A case study on ground vertebrates in tropical mountains

Empirical testing of the hypotheses for speciation, namely, allopatric (refugia model) and parapatric (gradient model) models, has been attempted using molecular phylogenetic methods by a case study on several groups of closely related species of small mammals inhabiting the Ethiopian Plateau. Comparison of the results with the available literature data on other ground vertebrates of tropical mountains has allowed us to demonstrate groundlessness of the currently popular concept on the significant role of parapatric speciation in formation of modern tropical biodiversity. It has been shown that a marked partition of altitudinal gradient by relatively close ground vertebrate species of tropical mountains in the majority of cases is secondary in nature and is not connected with the specific mode of their origination.

Development of an emission processing system for the Pearl River Delta Regional air quality modeling using the SMOKE model: Methodology and evaluation

Abstract An emission pre-processing tool is generally needed to transform a bulk annual emission inventory into gridded, temporal (monthly, weekly, and hourly), and speciated emissions in order to use complex air quality models such as the Community Multi-scale Air Quality (CMAQ) model to assess control strategies, forecast air quality, and investigate pollution formation and transport processes. To support the regional air quality modeling in the Pearl River Delta (PRD), we developed an emission pre-processing system, Sparse Matrix Operator Kernel Emissions-PRD (SMOKE-PRD), based on the U.S. Environmental Protection Agency (USEPA)/SMOKE model. This paper introduces the methods and procedures for adapting the SMOKE model to the PRD regional bulk emissions. These include the compilation of the PRD local source-class clarification codes, the incorporation of the PRD local emission inventory, and the updating of spatial, temporal, and chemical speciation information. The SMOKE-PRD system was evaluated, and a case study on ozone simulation was conducted to demonstrate the applicability of the SMOKE-PRD system. Results show that the model can properly simulate temporal variations, spatial patterns, and peak values of O3 concentrations in the PRD region, suggesting the SMOKE-PRD system was successfully localized and can be used to provide model-ready emissions for regional air quality modeling in the PRD region. This work can be extended for adapting the SMOKE model to process emissions for modeling use in other regions of China.

Applications of Time-Resolved Laser Fluorescence Spectroscopy to the Environmental Biogeochemistry of Actinides

Time-resolved laser fluorescence spectroscopy (TRLFS) is a useful means of identifying certain actinide species resulting from various biogeochemical processes. In general, TRLFS differentiates chemical species of a fluorescent metal ion through analysis of different excitation and emission spectra and decay lifetimes. Although this spectroscopic technique has largely been applied to the analysis of actinide and lanthanide ions having fluorescence decay lifetimes on the order of microseconds, such as UO , Cm, and Eu, continuing development of ultra-fast and cryogenic TRLFS systems offers the possibility to obtain speciation information on metal ions having room-temperature fluorescence decay lifetimes on the order of nanoseconds to picoseconds. The main advantage of TRLFS over other advanced spectroscopic techniques is the ability to determine in situ metal speciation at environmentally relevant micromolar to picomolar concentrations. In the context of environmental biogeochemistry, TRLFS has principally been applied to studies of (i) metal speciation in aqueous and solid phases and (ii) the coordination environment of metal ions sorbed to mineral and bacterial surfaces. In this review, the principles of TRLFS are described, and the literature reporting the application of this methodology to the speciation of actinides in systems of biogeochemical interest is assessed. Significant developments in TRLFS methodology and advanced data analysis are highlighted, and we outline how these developments have the potential to further our mechanistic understanding of actinide biogeochemistry.

Direct FexOy speciation in solid state materials by pulsed millisecond radio frequency glow discharge time-of-flight mass spectrometry

Although glow discharge mass spectrometry (GDMS) is best known for its utility in trace element analysis, recent work demonstrates that the technique can also provide chemical speciation information. Previous reports outline approaches for the direct speciation of chromium and manganese oxides utilizing GDMS. As that work illustrates, different approaches to speciation are needed depending on the metal oxide under study. The present work extends the application of this technique to the direct speciation of three iron oxide species in solid state samples. The appropriate adjustment of parameters such as sampling distance, temporal regime, discharge gas pressure, pulse frequency, and duty cycle is essential to enable such speciation. For the iron oxides, species specific variations in ratios between Fe+ and FeOH+ signal intensities provide the ability to discriminate between FeO, Fe2O3, and Fe3O4. Iron–oxygen cluster generation correlates with oxygen abundance in the original sample as seen in these comparisons.

Contribution to selenium speciation in cerebrospinal fluid samples

The well known beneficial health effects of Se have demanded the development of speciation methods for providing deeper insight into Se-metabolism and transport. This is also of significant importance for healthy brain function. Thus, Se-speciation was performed in 15 individual cerebrospinal fluid (CSF) samples (a′3 replicates) from neurologically healthy persons. First size exclusion chromatography (SEC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) equipped with a dynamic reaction cell (DRC) was used for monitoring the most abundant 80Se isotope. SEC separation provided Se-species characterization distinguishing between seleno-proteins and Se- low molecular mass (LMM) compounds. However, for improved speciation information a method based on strong anion exchange (SAX) separation was employed and optimized for CSF samples. The analysis of CSF samples from different individuals revealed six Se-species comprising relative mean concentrations of 8.5% (range: 5–11%), 27% (range: 20–31%), 2.2% (1.7–3.9%), 17% (range: 11–19%), 26% (range: 24–31%) and 20% (range: 19–21%) of the total Se amount, which in average was 3.6 μg L−1 (range: 2.9–4.8 μg L−1). Single and mixed Se-standard compounds were analyzed for verifying respective retention times, using serial UV- and ICP-MS detection. Additionally, standard additions were made to CSF samples for further peak identifications. By means of standard matching selenate, thioredoxinreductase (TrxR) and Se-albumin (Se-HSA) were found. No matches for Se methionine (SeM), Se-cystine (SeC), glutathioneperoxidase (GPx) and selenite were seen. Since no standard for selenoprotein P (SePP) was commercially available, this compound was prepared freshly from human serum using a Heparin-affinity column. It turned out that this SePP fraction showed matched retention time with the first peak in SAX separation, but also with selenate when age of the prepared standard was increasing.

Speciation of copper and zinc in size-fractionated atmospheric particulate matter using total reflection mode X-ray absorption near-edge structure spectrometry

The health effects of aerosol depend on the size distribution and the chemical composition of the particles. Heavy metals of anthropogenic origin are bound to the fine aerosol fraction (PM 2.5). The composition and speciation of aerosol particles can be variable in time, due to the time-dependence of anthropogenic sources as well as meteorological conditions. Synchrotron-radiation total reflection X-ray fluorescence (SR-TXRF) provides very high sensitivity for characterization of atmospheric particulate matter. X-ray absorption near-edge structure (XANES) spectrometry in conjunction with TXRF detection can deliver speciation information on heavy metals in aerosol particles collected directly on the reflector surface. The suitability of TXRF-XANES for copper and zinc speciation in size-fractionated atmospheric particulate matter from a short sampling period is presented. For high size resolution analysis, atmospheric aerosol particles were collected at different urban and rural locations using a 7-stage May cascade impactor having adapted for sampling on Si wafers. The thin stripe geometry formed by the particulate matter deposited on the May-impactor plates is ideally suited to SR-TXRF. Capabilities of the combination of the May-impactor sampling and TXRF-XANES measurements at HASYLAB Beamline L to Cu and Zn speciation in size-fractionated atmospheric particulate matter are demonstrated. Information on Cu and Zn speciation could be performed for elemental concentrations as low as 140 pg/m 3. The Cu and Zn speciation in the different size fraction was found to be very distinctive for samples of different origin. Zn and Cu chemical state typical for soils was detected only in the largest particles studied (2–4 μm fraction). The fine particles, however, contained the metals of interest in the sulfate and nitrate forms.

Evidence for Strong but Dynamic Iron−Humic Colloidal Associations in Humic-Rich Coastal Waters

This study investigated the physicochemical forms of dissolved iron in the coastal plume (salinity = 28-35) of a small river draining a peat-rich catchment. Speciation information was obtained through a combination of fractionation by crossflow filtration (CFF) along with voltammetric detection of either naturally occurring iron-humic complexes (July survey) or known, synthetic complexes (September survey) formed by titrating the samples with the competing ligand 2-(2-thiazolylazo)-p-cresol (TAC). The majority of colloidal iron (>5000 Da) was present as iron-humic complexes supplied by the river and showing uniform conditional stability constants throughout the plume (log K′(Fe′HS) = 11.3 ± 0.1, i.e. log K(Fe₃+HS) = 21.3 ± 0.1). Noncolloidal or soluble iron was strongly complexed to ligands of marine origin with log K′(Fe′HS) = 11.9 ± 0.1. Equilibrium of the total iron pool with the added TAC ligand was achieved in all but the highest salinity sample, albeit more slowly for colloidal than for soluble iron. In addition, measurements of humic like fluorescence suggested that the conformation of colloids could change over time as a result of dissociation of the iron-humic associations. These results are consistent with the concept that iron in coastal waters is strongly but reversibly bound to humic substances and therefore may be available for complexation by siderophore-type ligands released by microorganisms.

Chemical Transformations during Aging of Zerovalent Iron Nanoparticles in the Presence of Common Groundwater Dissolved Constituents

Nanoscale zerovalent iron (NZVI) that was aged in simulated groundwater was evaluated for alterations in composition and speciation over 6 months to understand the possible transformations NZVI could undergo in natural waters. NZVI was exposed to 10 mN of various common groundwater anions (Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), and HCO(3)(-)) or to dissolved oxygen (saturated, approximately 9 mg/L). Fresh and exposed NZVI samples, along with Fe-oxide model compounds, were then analyzed using synchrotron radiation X-ray absorption spectroscopy (XAS) to yield both relative oxidation state, using the X-ray absorption near edge structure (XANES), and quantitative speciation information regarding the types and proportions of mineral species present, from analysis of the extended X-ray absorption fine structure (EXAFS). Over 1 month of aging the dissolved anions inhibited the oxidation of the NZVI to varying degrees. Aging for 6 months, however, resulted in average oxidation states that were similar to each other regardless of the anion used, except for nitrate. Nitrate passivated the NZVI surface such that even after 6 months of aging the particles retained nearly the same mineral and Fe(0) content as fresh NZVI. Linear least-squares combination fitting (LCF) of the EXAFS spectra for 1 month-aged samples indicated that the oxidized particles remain predominantly a binary phase system containing Fe(0) and Fe(3)O(4), while the 6 month aged samples contained additional mineral phases such as vivianite (Fe(3)(PO(4))(2).8H(2)O) and iron sulfate species, possibly schwertmannite (Fe(3+)(16)O(16)(OH,SO(4))(12-13).10-12H(2)O). The presence of these additional mineral species was confirmed using synchrotron-based X-ray diffraction (XRD). NZVI exposed to water saturated with dissolved oxygen showed a rapid (<24 h) loss of Fe(0) and evolved both magnetite and maghemite (gamma-Fe(2)O(3)) within the oxide layer. These findings have implications toward the eventual fate, transport, and toxicity of NZVI used for groundwater remediation.

Synchrotron X-ray fluorescence analysis in environmental and earth sciences

Compared to other microscopic analytical tools X-ray microscopy techniques have the advantage that the large penetration depth of X-rays in matter allows one to investigate the interior of an object without destructive sample preparation. In combination with X-ray fluorescence tomography, analytical information from inside of a specimen can be obtained. Different X-ray analytical techniques can be used to produce contrast, X-ray absorption, fluorescence, and diffraction, to yield chemical, elemental, and structural information about the sample. Scanning microscopy on the basis of various lens systems in synchrotron radiation sources provides a routine spatial resolution of now about 100 nanometer but in the foreseeable future a 10–20 nanometer spatial resolution can be expected. X-ray absorption spectrometry can also provide chemical (speciation) information on the sample. All this makes X-ray microscopy attractive to many fields of science. In this paper the techniques are briefly reviewed and a number of applications in the earth, planetary and cosmos sciences are illustrated with state-of-the art examples, while applications in the environmental sciences and biology are also briefly discussed.

Methodology for the derivatization and quantification of dialkyl phosphate esters in petroleum samples

Dialkyl phosphate esters are used as gellants in some oil well fracturing processes for conventional oil production. Residual amounts of these compounds that remain in the well represent a source of potential contamination of the crude oil produced from the well. This contamination results in fouling of refinery equipment. Current methodologies for the analysis of alkyl phosphates have a relatively poor detection limit (0.5 ± 1.0 µg mL−1) and provide no speciation information: only a total phosphorus concentration. Herein, we present an approach that permits speciation of individual alkyl phosphates and quantification of individual compounds with limits of detection and precision that represent an improvement on the existing methodology. The method that we present relies upon derivatization of dialkyl phosphates to their trimethylsilane (TMS) esters followed by a comprehensive two-dimensional gas chromatographic separation. Two dialkyl phosphate esters, dibutyl and bis(2-ethylhexyl) phosphate were used as model compounds. Recovery of spiked samples in pure solvent and a model petroleum mixture ranged from 92% to 120%. This approach represents a significant first step in the development of an analytical solution to the challenge of phosphorus contamination facing the oil industry.

Extractive Electrospray Ionization Mass Spectrometry for Sensitive Detection of Uranyl Species in Natural Water Samples

Ambient mass spectrometry has been increasingly applied for sensitive detection of trace organic compounds present in complex matrixes. In the real world, detection of trace amounts of inorganic species, particularly with speciation information, is of great significances. Herein a method based on extractive electrospray ionization (EESI) tandem mass spectrometry (MS/MS) has been established for rapid detection of radioactive inorganic species in natural water samples. Negatively charged uranyl acetate undergoes characteristic fragmentation in the gas phase, providing the fundamental chemistry for specific detection of uranyl species in complex matrixes without sample pretreatment. Under the optimized experimental conditions, uranyl species in various natural water samples were rapidly detected using multiple-stage EESI mass spectrometry. The mean time for each sample analysis was about 10 s. The limit of detection was about a few 10(-3) ng/L of uranium by utilizing the characteristic fragments obtained in the EESI-MS(3) experiments. The typical relative standard deviation (RSD) of this method was 6.9-8.1% for 8 measurements (S/N = 3). The dynamic response range was 10(-1)-10(3) ng/L for uranium in water samples. The isotope ratio of uranyl species was quantitatively detected using EESI-MS experiments. The results show that EESI-MS, a typical method initially developed for organic compound analysis, has promising perspectives for real time, online monitoring of inorganic species such as uranyl species in natural water samples.

The correlation of 113Cd NMR and 111mCd PAC spectroscopies provides a powerful approach for the characterization of the structure of Cd(II)-substituted Zn(II) proteins.

Cd(II) has been used as a probe of zinc metalloenzymes and proteins because of the spectroscopic silence of Zn(II). One of the most commonly used spectroscopic techniques is (113)Cd NMR; however, in recent years (111m)Cd Perturbed Angular Correlation spectroscopy ((111m)Cd PAC) has also been shown to provide useful structural, speciation and dynamics information on Cd(II) complexes and biomolecules. In this article, we show how the joint use of (113)Cd NMR and (111m)Cd PAC spectroscopies can provide detailed information about the Cd(II) environment in thiolate-rich proteins. Specifically we show that the (113)Cd NMR chemical shifts observed for Cd(II) in the designed TRI series (TRI = Ac-G(LKALEEK)(4)G-NH(2)) of peptides vary depending on the proportion of trigonal planar CdS(3) and pseudotetrahedral CdS(3)O species present in the equilibrium mixture. PAC spectra are able to quantify these mixtures. When one compares the chemical shift range for these peptides (from delta = 570 to 700 ppm), it is observed that CdS(3) species have delta 675-700 ppm, CdS(3)O complexes fall in the range delta 570-600 ppm and mixtures of these forms fall linearly between these extremes. If one then determines the pK(a2) values for Cd(II) complexation [pK(a2) is for the reaction Cd[(peptide-H)(2)(peptide)](+)-->Cd(peptide)(3)(-) + 2H(+)] and compares these to the observed chemical shift for the Cd(peptide)(3)(-) complexes, one finds that there is also a direct linear correlation. Thus, by determining the chemical shift value of these species, one can directly assess the metal-binding affinity of the construct. This illustrates how proteins may be able to fine tune metal-binding affinity by destabilizing one metallospecies with respect to another. More important, these studies demonstrate that one may have a broad (113)Cd NMR chemical shift range for a chemical species (e.g., CdS(3)O) which is not necessarily a reflection of the structural diversity within such a four-coordinate species, but rather a consequence of a fast exchange equilibrium between two related species (e.g., CdS(3)O and CdS(3)). This could lead to reinterpretation of the assignments of cadmium-protein complexes and may impact the application of Cd(II) as a probe of Zn(II) sites in biology.

Preparation and methodology for chemical mapping of sol–gel thin films containing lysozyme

Sol–gels are seeing widespread interest as suitable materials for the immobilization of biomolecules in applications ranging from optical coatings to specialty biocatalysts. Although there are numerous studies that have characterized these materials in terms of their macroscopic properties, few studies have examined and correlated these properties at the microscopic level. This study describes a spin-coating technique for the preparation of aluminum-supported sol–gel thin films containing immobilized lysozyme [E.C. 3.2.1.17] that are suitable for chemical mapping using FTIR microscopy operating in reflectance mode. This type of information can then be used to understand a variety of aspects of these materials which can be used for optimal engineering of these materials, as well as insightful design and modeling. A data analysis method was developed to extract information on chemical speciation and domain information on the materials from FTIR data matrices. Results from these studies indicated that, contrary to what might be expected, these sol–gels are not homogeneous on the microscopic level. Instead, they are heterogeneous in both the distribution of lysozyme and hydrophobic monomers at the scale investigated (20 μm resolution). The method described here has promise in terms of providing a non-invasive approach of chemically mapping concentrations of proteinaceous and related substances as well as chemical domains in situ in sol–gel thin films.

Determination of inorganic selenium species [Se(IV) and Se(VI)] in tube well water samples in Punjab, India

Tube-well water samples in several parts of the Northeastern region of Indian Punjab, where extensive cases of selenosis were reported earlier, have been analyzed for Se(IV) and Se(VI). The total selenium in tube well water samples range from 12 to 93 μgL−1. No speciation information has been reported so far in these water samples. Bioavailability of selenium from water is affected by its various chemical forms. As selenate and selenite are the dominant forms of Se in water, an ion-chromatography–inductively coupled plasma mass spectrometry (IC–ICPMS) method was developed for the on-line separation of selenite [Se(IV)] and selenate [Se(VI)] and their determination in the tube well water samples. The selenium species were separated using an anion exchange column. A good baseline separation of both the species was obtained within 11 minutes. The detection limits for the Se species are Se(IV) = 0.3μgL−1 and Se(VI) = 0.8μgL−1. An eluent suppressor was used after the analytical column to reduce the salt content of the eluent: NaOH and the water sample. The dominant selenium species identified in these tube well water samples was found to be Se(VI). The concentration of total inorganic selenium in many of the water samples analyzed in this study exceeded the WHO limit (10μgL−1).

Mitochondrial phylogeography and population history of finless porpoises in Sino-Japanese waters

Phylogeographical patterns of intraspecific variation can provide insights into the population-level processes responsible for speciation and yield information useful for conservation purposes. In the present study, three hundred and forty-five base pairs of the mitochondrial DNA control region were sequenced to analyse the genetic diversity, population structure and history, and phylogeography of finless porpoises (Neophocaena phocaenoides) in Chinese and Japanese waters of the North Pacific. Nucleotide and haplotype diversities were 0.44% and 0.79 ± 0.01 for Chinese and Japanese waters, respectively, but varied significantly among populations. Analysis of molecular variance showed a high level of genetic structure between populations (ΦST = 0.61, P < 0.001; FST = 0.52, P < 0.001). Eleven of 18 haplotypes were restricted to a single population, common haplotypes were found in two to four populations, but no haplotype was found throughout Sino-Japanese waters, suggesting multiple colonization events followed by limited gene flow. The inferred age of demographic expansion was from the end stage of the last ice age to the Holocene. No obvious phylogeographical pattern was revealed, including between saline and fresh water populations. A low level of genetic diversity for each population and high among-population differentiation in haplotype frequency were revealed, which suggest a role for random genetic drift, recent demographic bottlenecks, and reduced or limited gene flow in these populations. Some conservation considerations, with special reference to the unique Yangtze population, are discussed. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 193–204.

Selenium Speciation Assessed by X-Ray Absorption Spectroscopy of Sequentially Extracted Anaerobic Biofilms

Wet chemical methods such as sequential extraction procedures are commonly used to assess selenium fractionation in anoxic environments, allowing an estimation of the mobility and bioavailability of selenium. However, the interpretation can be biased by unselective extraction of targeted species and artifacts introduced during the extraction. Here, the selectivity of the single extraction steps to gain reliable selenium speciation information are scrutinized for the first time by direct, nondestructive X-ray absorption near edge structure (XANES) spectroscopy at the selenium K-edge. The sequential extraction procedures seriously overestimated the elemental selenium fraction, as major parts (58%) of the total selenium were present as metal selenides and organic selenium compounds, although extracted in the elemental fraction. Spectral fitting of the XANES spectra by the least-squares linear combinations utilizing a large set of model compounds, including previously neglected Se(-I) selenides, showed a novel degree of complexity in the speciation of selenium treating anaerobic biofilms, with up to 4 modeled selenium species contributing to the speciation, i.e., different elemental, organic, and metal-bound selenium species. Furthermore, a short exposure (10 min) to ambient air during the sequential extraction procedure induced the oxidation of organic selenium compounds, revealing the fragility of selenium speciation in anaerobic biofilms.

Multispectral Analysis of Aerosols Over Oceans Using Principal Components

Applying principal component analysis (PCA) to one month of Moderate Resolution Imaging Spectroradiometer (MODIS) narrow-band short-wave radiance data and comparing with the Goddard Global Ozone Chemistry Aerosol Radiation Transport (GOCART) model simulations, we show that aerosol size and speciation information can be inferred from multispectral radiance information without having to use other parameters, such as a fine mode fraction (FMF), that are difficult to validate. PCA was applied to seven highly correlated MODIS solar channels (0.47, 0.55, 0.66, 0.86, 1.24, 1.64, and 2.12 mum) to extract noncorrelated pseudochannels, each with a unique interpretation. The first pseudochannel (PCI) can be interpreted as the mean radiance across the seven channels, which is directly proportional to the aerosol concentration. The second pseudochannel (PC2) is sensitive to the aerosol size since different aerosol types scatter and absorb differently across the seven MODIS short-wave channels. PC3 is inversely related to the aerosol optical thickness (AOT) and the FMF and appears most sensitive to changes in sulfate and maritime sea-salt concentrations. Results indicate that high values of PCI are indicative of high dust aerosol concentrations comprising more than 40% of the total AOT, whereas high values of PC2 indicate anthropogenic aerosol concentrations (deduced from GOCART) in excess of 60%. Compared to simple 0.55-mum FMF thresholds, the PC channels are much more sensitive to dust aerosol concentrations and certain aspects of anthropogenic aerosols, with very low FMF values alone (< 0.2) being the best indicator of predominately sea-salt aerosol concentrations. Our results indicate that PCA could be used as an alternate method for inferring aerosol speciation information in future research over ocean and more complex land surfaces.

Synchrotron microanalytical methods in the study of trace and minor elements in apatite

Synchrotron microanalytical methods in the study of trace and minor elements in apatiteSynchrotron X-ray facilities have the capability for numerous microanalytical methods with spatial resolutions in the micron to submicron range and sensitivities as low as ppm to ppb. These capabilities are the result of a high X-ray brilliance (many orders of magnitude greater than standard tube and rotating anode sources); a continuous, or white, spectrum through the hard X-ray region; high degrees of X-ray columniation and polarization; and new developments in X-ray focusing methods. The high photon flux and pulsed nature of the source also allow for rapid data collection and high temporal resolution in certain experiments. Of particular interest to geoscientists are X-ray fluorescence microprobes which allow for numerous analytical techniques including X-ray fluorescence (XRF) analysis of trace element concentrations and distributions; X-ray absorption spectroscopy (XAS) for chemical speciation, structural and oxidation state information; X-ray diffraction (XRD) for phase identification; and fluorescence microtomography (CMT) for mapping the internal structure of porous or composite materials as well as elemental distributions (Newville et al. 1999; Sutton et al. 2002; Sutton et al. 2004).We have employed several synchrotron based microanalytical methods including XRF, microEXAFS (Extended X-ray Absorption Fine Structure), microXANES (X-ray Absorption Near Edge Structure) and CMT for the study of minor and trace elements in apatite (and other minerals). We have also been conducting time resolved X-ray diffraction to study nucleation of and phase transformations among precursor phases in the formation of apatite from solution at earth surface conditions. Summaries of these studies are given to exemplify the capabilities of synchrotron microanalytical techniques.