Dominant Ion Research Articles

Structural derivation of lipid A from Cronobacter sakazakii using tandem mass spectrometry.

Cronobacter sakazakii is a Gram-negative opportunistic pathogen that can cause necrotizing enterocolitis, bacteremia, and meningitis. Lipid A, the glycolipid membrane anchor of lipopolysaccharide (LPS), is a potential virulence factor for C. sakazakii. Given the potential importance of this molecule in infection and virulence, structural characterization of lipid A was carried out. The structural characterization of lipid A extracted from C. sakazakii was performed using electrospray ionization and collision-induced dissociation in a linear ion trap mass spectrometer. Specifically, for detailed structural characterization, hierarchical tandem mass spectrometry was performed on the dominant ions present in the precursor ion mass spectra. By comparing the C. sakazakii fragmentation pathways to those of the known structure of E. coli lipid A, a structure of C. sakazakii lipid A was derived. The precursor ion at m/z 1796 from C. sakazakii is produced from a lipid A molecule where the acyl chains between the 2'b (C14) and 3'b (C12) positions are reversed as compared to E. coli lipid A. Additionally, the precursor ion at m/z 1824 from C. sakazakii corresponds to an E. coli structure with the same acyl chain at the 2'b position (C14), but a longer acyl chain (C14) at the 3'b position versus m/z 1796. Two lipid A structures were derived for the C. sakazakii ions at m/z 1796 and 1824. They differed in composition at the 2'b and 3'b acyl chain substituents, which may be a result of differences in substrate specificity of the two lipid A acyl chain transferases: LpxL and LpxM. Copyright © 2016 John Wiley & Sons, Ltd.

Interaction of Rahaliya\u2013Ekhedhur groundwater with the aquifer rock, West Razzaza Lake, Central Iraq

The groundwater of Dammam aquifer in Rahaliya–Ekhedhur area, West Razzaza, Iraq, was studied to identify the main hydrogeochemical processes and the groundwater–rock interaction. The results indicated that Na+ and SO42− are the dominant ions in the groundwater. The average contribution of cations in the aquifer is Na+ + K+ (24.7 %), Ca2+ (13.9 %), and Mg2+ (11.4 %), while anions contribution is SO42− (23.0 %), Cl− (20.7 %), and HCO3− (6.3 %). The groundwater characterized by neutral to slightly alkaline hard water, excessively mineralized, and slightly brackish water type. Rock–water interaction processes are identified to include dissolution of carbonates, sulfates, halite, and clay minerals, leaching, and cation exchanges, with little impact of evaporation.

A solvable blob-model for magnetized plasmas

A simple analytically solvable model for blobs in magnetized plasmas is proposed. The model gives results for a scaling of the blob velocity and acceleration with varying plasma parameters. Limiting cases are considered: one where the plasma motion is strictly perpendicular to an externally imposed toroidal magnetic field, and one where the electrons can move along magnetic field lines to compensate partly the collective electric fields. For these limiting cases, the model predicts scaling laws for the dependence of the blob velocities and accelerations with varying plasma density, temperature and magnetic field strength. Also the scaling with the dominant ion mass is derived. The analysis is completed by including the effects of collisions between ions and neutrals.

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth.

Potassium channels importantly contribute to the regulation of vascular smooth muscle (VSM) contraction and growth. They are the dominant ion conductance of the VSM cell membrane and importantly determine and regulate membrane potential. Membrane potential, in turn, regulates the open-state probability of voltage-gated Ca2+ channels (VGCC), Ca2+ influx through VGCC, intracellular Ca2+, and VSM contraction. Membrane potential also affects release of Ca2+ from internal stores and the Ca2+ sensitivity of the contractile machinery such that K+ channels participate in all aspects of regulation of VSM contraction. Potassium channels also regulate proliferation of VSM cells through membrane potential-dependent and membrane potential-independent mechanisms. VSM cells express multiple isoforms of at least five classes of K+ channels that contribute to the regulation of contraction and cell proliferation (growth). This review will examine the structure, expression, and function of large conductance, Ca2+-activated K+ (BKCa) channels, intermediate-conductance Ca2+-activated K+ (KCa3.1) channels, multiple isoforms of voltage-gated K+ (KV) channels, ATP-sensitive K+ (KATP) channels, and inward-rectifier K+ (KIR) channels in both contractile and proliferating VSM cells.

Diurnal dynamics of minor and trace elements in stream water draining Dongkemadi Glacier on the Tibetan Plateau and its environmental implications

Global warming has resulted in rapid glacier retreat on the Tibetan Plateau (TP), and the impacts of glacier melting on downstream ecosystems remain largely unknown. Minor and trace elements in stream water draining Dongkemadi Glacier (DG) were examined during the ablation season of 2013. Dominant ions and elements are HCO3−, Ca2+, Fe and Sr. Water chemistry is controlled by the weathering of calcite, oxidation of pyrite and dissolution of evaporites. Correlations suggests the hydrological (e.g. meltwater generation and routing, water residence time) and physicochemical (e.g. sorption, precipitation, oversaturation) controls on species concentrations. The distribution of metals is featured by the mixture of soluble metal and non-metal ligand complexes and free monovalent and divalent ions. Downstream increased concentrations and/or fluxes of some metals and metalloid (e.g. Cr, Cu and As) suggest potential environmental impacts. Discharge-normalized cation denudation rate (372Σ∗meq+m−3) in the DG basin is larger than those from alpine and polar glaciers, suggesting a stronger weathering of carbonate with greater abundance on the TP in comparison to other mountain and polar glacial catchments. The maximum Fe concentration exceeds the USEPA guideline, and Al, Zn and Pb are close to or of the same order of magnitude as liminal values. This implies that the TP may face a challenge of ecosystem health and environmental issue in a warming climate.

Compositional data analysis as a robust tool to delineate hydrochemical facies within and between gas‐bearing aquifers

AbstractIsometric log ratios of proportions of major ions, derived from intuitive sequential binary partitions, are used to characterize hydrochemical variability within and between coal seam gas (CSG) and surrounding aquifers in a number of sedimentary basins in the USA and Australia. These isometric log ratios are the coordinates corresponding to an orthonormal basis in the sample space (the simplex). The characteristic proportions of ions, as described by linear models of isometric log ratios, can be used for a mathematical‐descriptive classification of water types. This is a more informative and robust method of describing water types than simply classifying a water type based on the dominant ions. The approach allows (a) compositional distinctions between very similar water types to be made and (b) large data sets with a high degree of variability to be rapidly assessed with respect to particular relationships/compositions that are of interest. A major advantage of these techniques is that major and minor ion components can be comprehensively assessed and subtle processes—which may be masked by conventional techniques such as Stiff diagrams, Piper plots, and classic ion ratios—can be highlighted. Results show that while all CSG groundwaters are dominated by Na, HCO3, and Cl ions, the proportions of other ions indicate they can evolve via different means and the particular proportions of ions within total or subcompositions can be unique to particular basins. Using isometric log ratios, subtle differences in the behavior of Na, K, and Cl between CSG water types and very similar Na‐HCO3water types in adjacent aquifers are also described. A complementary pair of isometric log ratios, derived from a geochemically‐intuitive sequential binary partition that is designed to reflect compositional variability within and between CSG groundwater, is proposed. These isometric log ratios can be used to model a hydrochemical pathway associated with methanogenesis and/or to delineate groundwater associated with high gas concentrations.

Barium Sulfate Crystallization from Synthetic Seawater

Barium sulfate was crystallized in a synthetic seawater mixture that was chosen to better reflect ocean conditions. The synthetic seawater contained monovalent ions, magnesium, strontium, and calcium as well as bicarbonate and boric acid. The natural pH of the synthetic seawater is 8.1, and this seawater was used to determine the impact on morphology, nucleation rates, and incorporation of foreign ions. It was found that dendritic and diamond-shaped particles are both formed. The main parameters influencing the formation of dendritic particles were the saturation index and the ion ratio, but there was also a significant synergistic effect with the other ions present. The diamond-shaped particles formed later at a lower saturation index. The nucleation rate in synthetic seawater was found to be higher than expected based on an ion ratio basis. This is most probably because the divalent ions induce a higher nucleation rate by lowering the surface free energy. Strontium was found to be the dominant ion subst...

Preparation of pulsed DC magnetron deposited Fe‐doped SnO2 coatings

Iron‐doped SnO2 coatings were deposited in a 50 kHz DC‐pulsed magnetron sputtering discharge. The pulses had a duration of 4 μs in selected gas mixtures from pure argon up to 60% of oxygen at a constant total pressure of 0.2 Pa. A single target of SnO2 with Fe inset was used. The mass spectrometry study detected the gas‐related ions Ar+, O2+ and O+, where the last one becomes the dominant positive ion at higher oxygen contents. Atomic oxygen ions had a higher energy as it resulted from the collision‐caused dissociation on the target surface. The tin‐related species were detected as Sn+ and SnO+. SnO2+ species were not detected. The deposition rate decreased by using gas mixtures with oxygen as well as the corresponding amount of Sn‐related species in the plasma. The increase of oxygen also increased significantly the sheet resistance of the films. The XPS study showed that the iron concentration decreased by using additional oxygen. But the O/Sn ratio in the coatings was constant, contrary to the increased FeO/Fe ratio in the films. An additional analysis of the coatings by spectroscopic ellipsometry has shown a dependence of the polarizability and the permittivity on the amount of oxygen used during the deposition. In contrast, the study has found no such dependence for the absorption of the layers.

Multiply Reduced Oligofluorenes: Their Nature and Pairing with THF-Solvated Sodium Ions

Conjugated oligofluorenes are chemically reduced up to five charges in tetrahydrofuran solvent and confirmed with clear spectroscopic evidence. Stimulated by these experimental results, we have conducted a comprehensive computational study of the electronic structure and the solvation structure of representative oligofluorene anions with a focus on the pairing between sodium ions and these multianions. Using density functional theory (DFT) methods and a solvation model of both explicit solvent molecules and implicit polarizable continuum, we first elucidate the structure of tightly solvated free sodium ions, and then explore the pairing of sodium ions either in contact with reduced oligofluorenes or as solvent-separated ion pairs. Computed time-dependent-DFT absorption spectra are compared with experiments to assign the dominant ion pairing structure for each multianion. Computed ion pair binding energies further support our assignment. The availability of different length and reducing level of oligofluorenes enables us to investigate the effects of total charge and charge density on the binding with sodium ions, and our results suggest both factors play important roles in ion pairing for small molecules. However, as the oligofluorene size grows, its charge density determines the binding strength with the sodium ion.

Sources of chemical species in rainwater during monsoon and non-monsoonal periods over two mega cities in India and dominant source region of secondary aerosols

Samples of rainwater (RW) were collected to characterize the chemistry and sources in two representative megacities at Pune (Southwest) and Delhi (Northern) India from 2011 to 2014 across two seasons: monsoon (MN) and non-monsoon (NMN). Collected RW samples were analyzed for major chemical constituents (F−, Cl−, SO42−, NO3−, NH4+, Na+, K+, Ca2+, and Mg2+), pH and conductivity. In addition, bicarbonate (HCO3−) was also estimated. The mean pH values of the RW were >6 at Pune and <6 at Delhi and 4% and 26% were acidic, respectively. The mean sum of all measured ionic species in Pune and Delhi was 304.7 and 536.4 μeq/l, respectively, indicating that significant atmospheric pollution effects in these Indian mega cities. Both the Ca2+ and SO42− were the dominant ions, accounting for 43% (Pune) and 54% (Delhi) of the total ions. The sum of measured ions during the NMN period was greater than the NM period by a factor of 1.5 for Pune (278.4: NM and 412.1: NMN μeq/l) and a factor of about 2.5 for Delhi (406 and 1037.7 μeq/l). The contributions of SO42− and NO3− to the RW acidity were ∼40% and 60%, respectively, at Pune and correspondingly, 36% and 64% at Delhi. The concentrations of secondary aerosols (SO42−and NO3−) were higher by a factor of two and three when the air masses were transported to Pune from the continental side. At Delhi, the concentrations of SO42−, NO3−, Ca2+, and Mg2+ were significantly higher when the air masses arrive from Punjab, Haryana, and Pakistan indicating the greater atmospheric pollution over the Indo-Gangetic Plain. Positive matrix factorization was applied to the source apportionment of the deposition fluxes of these ions. Three factors were obtained for Pune and four for Delhi. The sources at Pune were secondary aerosols from fossil fuel combustion, soil dust, and marine, whereas, at Delhi, the sources were soil, fossil fuel combustion, biomass burning, and industrial chlorine.

Arsenic and heavy metal contaminations in the tube well water of Punjab, Pakistan and risk assessment: A case study

The present study for the first time highlighted the arsenic and heavy metals (HM) concentrations as well as their source of contamination in tube-well water and associated potential health risk to local residents of Tehsil Mailsi (Punjab), Pakistan. 44 samples were collected from Jala Jeem and Dunia Pur. Results revealed average concentrations of anion and heavy metals such as Iron (Fe), (Cadmium) Cd, (Lead) Pb, (Sodium) Na+, (Bicarbonate) HCO3−, (Sulfate) SO42− and Arsenic (As) exceeded the WHO limits in the tube well water. The calculated target hazard quotient (THQ) of metals from local tube well water above 1 was observed for As (36.5) and Cd (6.2), which employed highly potential health risk to local residents. The suitability of water for irrigation is evaluated based on residual sodium carbonate (RSC), sodium adsorption ratio (SAR), Kelly’s index (KI), Sodium percent (%Na) and Magnesium absorption ratio (MAR). Dominant ions in the study area are HCO3−, Ca2+ and Mg2+ and water chemistry of the area is Ca2+-Mg2+-HCO3− type. However, different statistical tools, including principal component analysis (PCA), hierarchical cluster analysis (CA) and correlation matrices revealed the contribution of both natural as well as anthropogenic activities towards the high level of arsenic and heavy metals contamination in the local tube well water. The results show that consumption of heavy metals contaminated groundwater poses an emerging health threat to the populations in the study area, and hence needs urgent remedial and management measures. Continued monitoring of heavy metals levels is recommended for future management strategies.

Geochemical Characterization of Fluoride in the Groundwater of the Huaibei Plain, China

ABSTRACTForty-two groundwater samples were collected for the geochemical characterization of fluoride in the Huaibei Plain, a high fluorine area, in Northern China. The concentration of fluoride in the groundwater was from 0.20 to 3.75 mg/L, and 23.81% (n = 9) of the samples exceeded the drinking water standard of 1.5 mg/L recommended by the World Health Organization. The groundwater was alkaline (pH 7.14–8.67), brackish (total dissolved solids 421–1196 mg/L), and the water was classified as sodium bicarbonate, calcium bicarbonate, calcium–sodium bicarbonate, and chloride–sodium bicarbonate. This prevailing characteristic may be attributed to mineral weathering, water–rock interactions, and ion exchange in the aquifer. The main source of fluorine in the groundwater may be from the leaching of minerals. The elevated concentration of fluoride in groundwater may be derived from the calcite–fluorite minerals. This study also discusses several factors affecting the fluoride concentrations in groundwater. High fluoride concentrations are associated with weakly alkaline conditions, moderate total dissolved solids, and calcium and sodium ions as the dominant ions. Correlations between fluoride and sample depth and were not observed. All samples were below the solubility product curve of CaF2, which may be explained by positive correlation between fluoride and total dissolved solids. Evapotranspiration and runoff conditions also favor fluoride enrichment in groundwater.

New insights into methane-oxygen ion chemistry

External electric fields may reduce emissions and improve combustion efficiency by active control of combustion processes. In-depth, quantitative understanding of ion chemistry in flames enables predictive models to describe the effect of external electric fields on combustion plasma. This study presents detailed cation profile measurements in low-pressure, burner-stabilized, methane/oxygen/argon flames. A quadrupole molecular beam mass spectrometer (MBMS) coupled to a low-pressure (P=30Torr) combustion chamber was utilized to measure ion signals as a function of height above the burner. Lean, stoichiometric and rich flames were examined to evaluate the dependence of ion chemistry on flame stoichiometry. Additionally, for the first time, cataloging of flame cations is performed using a high mass resolution time-of-flight mass spectrometer (TOF-MS) to distinguish ions with the same nominal mass. In the lean and stoichiometric flames, the dominant ions were H3O+, CH3O2+, C2H7O+, C2H3O+ and CH5O+, whereas large signals were measured for H3O+, C3H3+ and C2H3O+ in the rich flame. The spatial distribution of cations was compared with results from numerical simulations constrained by thermocouple-measured flame temperatures. Across all flames, the predicted H3O+ decay rate was noticeably faster than observed experimentally. Sensitivity analysis showed that the mole fraction of H3O+ is most sensitive to the rate of chemi-ionization CH+O↔CHO++E−. To our knowledge, this work represents the first detailed measurements of positive ions in canonical low-pressure methane flames.

Two-dimensional simulations of a VHF H2 plasma for different discharge gaps and gas pressures

A two-dimensional simulation on a VHF H2 plasma (60 MHz) was performed using the plasma hybrid code, and plasma parameters were examined as a function of pressure for different discharge gaps. It was found that as the pressure increased, the H3+ and H+ densities as well as the electron density had a maximum at a certain pressure, and the maximum shifted to high pressures as the discharge gap decreased. On the other hand, the H2+ density decreased with the increase in pressure, independent of the discharge gap. The axial profiles of the H+, H2+, and H3+ densities showed that dominant ions were H3+ in our pressure range.

Insight into structural feature of the extraction residue from Shenmu coal char powder

Ruthenium ion-catalyzed oxidation of the extraction residue from Shenmu coal char powder (ERSCCP) was conducted. The resulting soluble portions (SPs) were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and direct analysis in real time/time-of-flight mass spectrometer (DART/TOF-MS) to obtain carboxylic acids and to understand the structural feature of ERSCCP. The results show that benzenepolycarboxylic acids with 3–6 carboxy groups are predominant in the SPs, suggesting that ERSCCP is rich in highly condensed aromatic moieties. In addition, small amounts of long-chain alkanoic acids were detected with GC/MS. According to analysis with positive-ion DART/TOF-MS, [M - OCH3]+ and [M+NH4]+are dominant ions generated from polymethylbenzenepolycarboxylates (PMBPCs) in the methyl esterified SPs. A series of dimers and trimers of PMBPCs were also identified with positive-ion DART/TOF-MS.

Comparative study of ground water treatment plants sludges to remove phosphorous from wastewater

Alum- and iron-based sludge obtained from water treatment plant produced during a unit treatment process (coagulation and flocculation) have been widely tested as a low-cost adsorbent to remove phosphorous (P) from wastewater. However, the effectiveness of iron-based sludge generated from the oxidation of iron which naturally occurs in the ground water has not been investigated. Moreover, influences of dominant metals ions comprised in the treatment plants sludges on P adsorption capacity and rate from wastewater are not yet known. This study, therefore, employed four different groundwater treatment plants sludges iron-based (from the oxidation of iron) and alum-based (from coagulation and flocculation process) to determine their P adsorption capacities and adsorption rates from the synthetic wastewater (SWW) and secondary effluent wastewater (SEWW). Although metals ions concentrations were the highest in the iron-based sludge amongst the sludge used in this study, it appeared to have the lowest P adsorption capacity and adsorption rate. A good correlation between aluminium to iron mass ratio and adsorption capacity for both types of waters were noted. However, a poor relation between aluminium to iron mass ratio and adsorption rates for the SEWW was observed. Further, the tested sludges were found to have a better P removal efficiency and adsorption capacity from the SEWW than from the SWW. Thus, this study demonstrates the ground water treatment plants sludges could be a low cost and effective adsorbent in removing P from wastewater.

Aerosol composition and sources during high and low pollution periods in Ningbo, China

Due to the rapid industrialization of the Yangtze River Delta (YRD) region in China, heavy air pollution episodes have occurred frequently over the past five years which are of great concern due to their environmental and health impacts. To investigate the chemical characteristics of the highly polluted aerosols in this region, a sampling campaign had been conducted in Ningbo from 3 December 2012 to 27 June 2013, during which a month long high pollution episode had been captured. Daily average PM2.5 concentrations during high and low pollution periods were 111μgm−3 and 53μgm−3, respectively. The most polluted day was 8 January 2013 with a PM2.5 concentration up to 175μgm−3. To understand the origin of the highly polluted aerosols, meteorological conditions, air mass backward trajectories, distribution of fire spots in surrounding areas and various categories of aerosol pollutants were analyzed, including trace metals, inorganic species, PAHs and anhydrosugars. Total metal concentrations were 3.8 and 1.6μgm−3 for the high and low pollution episodes, respectively, accounting for 3.4% and 3.1% of the total PM2.5 mass. Total concentrations of ionic species accounted for more than 50.0% of the PM2.5 by mass, with dominant ions (nitrate, sulfate, ammonium) accounting for over 42.0% of the PM2.5 mass concentrations in both periods. During the high pollution episode, enhanced Cd–Pb and biomarker (levoglucosan, mannosan) levels indicated the contributions from coal combustion, traffic and biomass burning to fine aerosol PM2.5. The average diagnostic ratio of Fla/(Fla+Pyr) was 0.54 in high pollution episode, which was intermediate between that for wood (>0.50) and coal combustion (0.58). BaP/Bpe was 0.49 and 0.30 for the highly and lightly polluted aerosols respectively, associated with the significant non-traffic emissions (<0.60). In addition, stagnant weather conditions during the high pollution period and long-range transport of air masses from heavy industries and biomass burning from northern China to Ningbo could be considered as the main factors for the formation of the aerosols during high pollution period.

Real-time diamagnetic flux measurements on ASDEX Upgrade.

Real-time diamagnetic flux measurements are now available on ASDEX Upgrade. In contrast to the majority of diamagnetic flux measurements on other tokamaks, no analog summation of signals is necessary for measuring the change in toroidal flux or for removing contributions arising from unwanted coupling to the plasma and poloidal field coil currents. To achieve the highest possible sensitivity, the diamagnetic measurement and compensation coil integrators are triggered shortly before plasma initiation when the toroidal field coil current is close to its maximum. In this way, the integration time can be chosen to measure only the small changes in flux due to the presence of plasma. Two identical plasma discharges with positive and negative magnetic field have shown that the alignment error with respect to the plasma current is negligible. The measured diamagnetic flux is compared to that predicted by TRANSP simulations. The poloidal beta inferred from the diamagnetic flux measurement is compared to the values calculated from magnetic equilibrium reconstruction codes. The diamagnetic flux measurement and TRANSP simulation can be used together to estimate the coupled power in discharges with dominant ion cyclotron resonance heating.

Donnan dialysis based separation of gold(III) from electronic waste solutions using an anion exchange pore-filled membrane

Donnan dialysis technique was employed for the recovery of Au(III) from aqua regia solutions of electronic waste containing low concentrations of Au(III) in the presence of much higher concentrations of Cu(II) and Ni(II). The anion exchange pore-filled membrane was synthesized using in-situ photo-polymerization with polypropylene as the host membrane and (3-acrylamidopropyl)trimethyl ammonium chloride and (3-acryloxy-propyl)trimethoxysilane as the monomer and spacer, respectively. Photo-polymerization was carried out with ethylene glycol dimethacrylate as the cross-linker and 2,2-dimethoxy-2-phenyl acetophenone as the UV-initiator. The transport of Au(III) through this anion-exchange pore-filled membrane was studied using a two compartment cell where the receiver solution contained NaCl as the stripping reagent. Cu(II), which is the dominant metal ion in electronic waste solutions, did not interfere with the transport of Au(III) even at Au(III): Cu(II) mass ratios of up to 1:500. Gold from 100-fold diluted electronic waste solutions in aqua regia was successfully recovered (96.3%) after 4 cycles of Au(III) transport while at the same time insignificant fractions of the dominant metals in the electronic scrap (Cu and Ni) were transported. This study shows that Au(III) can be selectively recovered from diluted aqua regia solutions of electronic waste based on the proposed Donnan dialysis process.

A one-year record of carbonaceous components and major ions in aerosols from an urban kerbside location in Oporto, Portugal

PM2.5 aerosol samples were collected from January 2013 to January 2014 on the kerbside of a major arterial route in the city of Oporto, Portugal, and later analyzed for carbonaceous fractions and water soluble ions. The average concentrations of organic carbon (OC), elemental carbon (EC) and water soluble organic carbon (WSOC) in the aerosol were 6.2μg/m3, 5.0μg/m3 and 3.8μg/m3, respectively, and fit within the range of values that have been observed close to major roads in Europe, Asia and North America. On average, carbonaceous matter accounted for 56% of the gravimetrically measured PM2.5 mass. The three carbon fractions exhibited a similar seasonal variation, with high concentrations in late autumn and in winter, and low concentrations in spring. SO42− was the dominant water soluble ion, followed by NO3−, NH4+, Cl−, Na+, K+, oxalate, Ca2+, Mg2+, formate, methanesulfonate and acetate. Some of these ions exhibited a clear seasonal trend during the study period. The average OC/EC ratio for the entire set of samples was 1.28±0.61, which was consistent with a significant influence of vehicle exhaust emissions on aerosol composition. On the other hand, the average WSOC/OC ratio was 0.67±0.23, reflecting the influence of other emitting sources. WSOC was highly correlated with nssK+, a tracer of biomass combustion, and was not correlated with nssSO42−, a species associated with secondary processes, suggesting that the main source of WSOC was biomass burning. Most of the SO42− was anthropogenic in origin and was closely associated with NH4+, pointing to the formation of secondary aerosols. Na+, Cl− and methanesulfonate were clearly associated with marine sources while NO3− was related with combustion of both fossil and non-fossil fuels. Mixed sources explained the occurrence of the other water soluble ions.