Varying Ion Concentrations Research Articles

Small-Scale Horizontal Variations in Ionic Concentrations of Bulk Deposition from Hong Kong

The concentrations of major anions andcations in bulk deposition were found to varyspatially by factors of up to 65, for two samplings at17 sampling sites separated by 45 km or less in theTerritory of Hong Kong. Under predominantly maritimeairstreams, these variations resulted from localemissions, as well as from lower seasaltconcentrations at the more northerly sites. The weakacidity of the bulk deposition resulted fromneutralization of hydrometeors by basic particulatematter, leading to an unusual anticorrelation of theconcentrations of non-seasalt sulphate and hydrogenions. Greater anthropogenic activity at inland andindustrial sites was generally marked by highernitrate concentrations, with the ratio of nitrate ionconcentrations from the two samplings being stronglycorrelated with that of calcium ion. Chloride lossincreased with increasing concentrations ofnon-seasalt nitrate and sulphate. Most of the variancein the bulk deposition data for 8 major anions andcations could be explained by 2 factors: seasalt andanthropogenic, in common with the 1997 EnvironmentalProtection Department data for these species in totalsuspended particulate matter. Results for 14 solubletrace metal species in the bulk deposition at thesites are also reported.

A General Approach to Modeling Conduction and Concentration Dynamics in Excitable Cells of Concentric Cylindrical Geometry

This paper discusses mathematical approaches for modeling the propagation of the action potential and ion concentration dynamics in a general class of excitable cells and cell assemblies of concentric cylindrical geometry. Examples include myelinated and unmyelinated axons, single strands of interconnected cardiac cells and outer hair cells. A key feature in some of the cells is the presence of a small working volume such as the periaxonal space between the myelin sheath and the axon in the myelinated axon and the extracisternal space between the plasma membrane and the subsurface cisterna of the outer hair cell. Proper treatment of these cell types requires a modeling approach which can readily address these anatomical properties and the non-uniform biophysical properties of the concentric membranes and the ionic composition of the volumes between the membranes. An electrodiffusion approach is first developed in which the Nernst–Planck equation is used to characterize axial ion fluxes. It is then demonstrated that this “full” model can be stepwise reduced, eventually becoming equivalent to the standard cable equation formulation. This is done in a manner that permits direct comparisons between the full and simplified models by running simulations using a single parameter set. An intermediate approach where the contributions of the axial currents to ion concentration changes and the effect of varying ion concentrations on solution conductivities are ignored is derived and is found adequate in many cases. Two application examples are given: a “cardiac strand” model, for which the intermediate formulation is shown sufficient and a model of the myelinated axon, for which the full electrodiffusion formulation is clearly necessary. The latter finding is due to spatial inhomogeneities in the anatomy and distribution of ion channels and transporters in the myelinated axon and the restricted periaxonal space between the myelin sheath and the axon.

Cloud droplet size dependence of the concentrations of various ions in cloud water at a mountain ridge in northern Japan

Acid precipitation is one of the global environmental problems affecting terrestrial and aquatic ecosystems. Our research group has recently studied the acid precipitation in Hyogo and Akita Prefectures in Japan, combining chemical analysis of ions with analysis of meteorological conditions, and has analyzed the source of pollutants by Ž . factor analysis Ozeki et al., 1995, 1997; Ogawa et al., 1998a,b . It is known that fogrcloud water is significantly more acidic and has higher concentrations of chemical Ž . components than rain water e.g., Waldman et al., 1982; Hosono et al., 1994 . The mechanism of uptake of ion components into cloud droplets, especially for the difference between ions, is not completely understood. Cloud water and rain water samples were collected at the Hachimantai mountain range in Akita Prefecture in northern Japan to obtain information on the mechanism of uptake of ion components into cloud droplets. The chemical composition of the cloud water was analyzed and compared with that of the rain water. The relationship among ion concentrations in the cloud water and droplet size was examined Ž X X Cloud water samples were collected along the mountainside 39856 N, 140851 E, . Ž . 1465 m, a.s.l. of Mt. Mokkodake 1578 m, a.s.l. , a mountain ridge in the Hachimantai Ž . Ž range. A passive fog sampler Okita, 1961 with a cylindrical Teflon wire screen Model . FWP-500, Usui Kogyo Kenkyusho was exposed during the period from August to Ž . September 1997. Rain water samples were collected at Akita City Akita University

A theoretical study of outersphere electron transfer reactions in electrolyte solutions

A microscopic theory of outersphere electron transfer reactions in electrolyte solutions is presented. Both static and dynamic effects of solvent and ion atmosphere on rates of electron transfer are calculated by employing molecular models. The donor–acceptor system is composed of two spheres and the electrolyte solution is composed of dipolar solvent molecules and ions which are treated at the same molecular level. A microscopic expression for the free energy of activation is derived by using density functional theory. The dynamic effects are calculated by using a molecular hydrodynamic theory which properly includes finite wave vector modes of relaxation of solvent and ion atmosphere. Explicit numerical results are presented for the activation free energy and the rate constant of electron transfer in solutions of varying ion concentration. It is found that ion atmosphere can make an important contribution to the activation free energy at finite ion concentration although the net increase in the activation energy is not very significant for the solutions studied in this work. This happens because, with increase of ion concentration, the ion atmosphere contribution to the total activation free energy increases, whereas the solvent contribution shows a decreasing trend. The solvent behaves as an effective less polar medium due to screening by ions and, therefore, its contribution to the activation free energy decreases as ion concentration is increased.

Selective permeability of a perfluorosulphonic membrane to different valency cations. Ion-exchange isotherms and kinetic aspects

Transport competition between protons and Ag +, Co 2+and Ce 3+ ions across a Nafion™ cation exchange membrane (CEM) has been studied in the Donnan exclusion domain. In such conditions the membrane does not contain any mobile anion but only cations (the counter-ions) which electrically equilibrate the sulphonic sites. In the frame of the gel-model, the ion transport flux depends on both the composition of the membrane resulting from the solution–membrane exchange equilibrium and the mobility of the counter-ions within the membrane. As the charge of the ion increases, so does its affinity for the membrane which is greater for multivalent counter-ions than for protons due to their larger electrostatic attraction towards the exchange sites of opposite polarity. On the other hand, as the charge of the ion increases, its mobility in the membrane is reduced. Modelling of this transport takes into account these two aspects as well as ionic concentration variations in the diffusion layer.

Spatial variability of snow chemistry in western Dronning Maud Land, Antarctica

During the austral summer of 1993-94 a number of 1-2 m deep snow pits were sampled in connection with firn-coring in western Dronning Maud Land, Antarctica. The traverse went from 800 to about 3000 m a.s.l. upon the high-altitude plateau. Profiles of cations (Na+, K+, Mg2+, Ca2+), anions (Cl−, NO3-, SO4 2- , CH3SO3 −) and stable oxygen isotopes (δ18O) from 11 snow pils are presented here. Close to the coast 2 m of snow accumulates in about 2-3 years, whilst at sites on the high-altitude plateau 2 m of snow accumulates in 10—14 years. The spatial variation in ion concentrations shows that the ions can be divided into two groups, one with sea-salt elements and methane sulfonate and the other with nitrate and sulfate. For the sca-salt elements and methane sulfonate the concentrations decrease with increasing altitude and increasing distance from the coast, as well as with decreasing temperature and decreasing accumulation rate. For nitrate and sulfate the concentrations are constant or increase with respect to these parameters. This pattern suggests that the sources for sca-salt elements and methane sulfonate are local, whereas the sources for nitrate and sulfate are a mixture of local and long-range transport.

Effects of ion atmosphere relaxation on dipole isomerization reactions in electrolyte solutions

A theoretical study of the effects of ion atmosphere relaxation on the rate of a model dipole isomerization reaction in electrolyte solutions is presented. The time-dependent ion atmosphere friction is calculated by using a molecular hydrodynamic theory which properly includes the static and dynamic interionic correlations through ionic structure factors and van Hove functions. The rate constant is determined by employing the well-known Grote-Hynes theory. Numerical results are obtained for the time-dependent ion atmosphere friction and for the rate of isomerization reaction in electrolyte solutions of varying ion concentration and dielectric constant. It is found that the ion atmosphere friction can have significant effects in reducing the rate of isomerization below the prediction of equilibrium solvation transition state theory.

Two Types of Stretch-Activated Channels Coexist in the Rabbit Corneal Epithelial Cell

Ion channels contribute to the regulation of cellular function through control of the membrane potential and intracellular concentration of various ions. We examined stretch-activated channels in the corneal epithelial cell. Patch clamping was applied to enzymatically dissociated corneal epithelial cells to characterize their stretch-activated ion channels. The plasma membrane was stretched by applying suction to the patch pipette in cell-attached or inside-out patch configuration. The ion selectivity, voltage-dependence, and stretch-dependence were examined. Two kinds of stretch-activated channel events were observed; the previously-reported large conductance (L) channel and a novel small conductance (S) channel. The probability of recording L vs. S channels in the cell-attached configuration was about 2:1. The L channel was potassium selective with single channel conductance (γ) of about 160 pS under the symmetrical (150 mmK+) solution. The S channel was permeable to Na+and K+with γof about 20 pS under the same conditions. Both L and S channels showed little activity in the absence of suction applied to the recording pipette. Channel activity was evoked by suction (negative pressure) stronger than -20 mmHg in both channels. The open probability (Po) and the mean current increased in proportion to further applied stretch and did not saturate for applied suction as strong as -80 mmHg, the pressure at which the gigaseal started to break. Thus, two types of stretch-activated channels coexist in corneal epithelial cells; a potassium-selective L channel and non-selective S channel. The contribution of these channels to the membrane potential is discussed.

Dynamics of electrolyte solutions at finite wave vectors: Theoretical results for ions in a molecular solvent

A molecular theory of the dynamics of ions and solvent molecules in electrolyte solutions is presented. The theory properly includes ion–ion, ion–solvent, and solvent–solvent molecular correlations through intra- and interspecies static structure factors and direct correlation functions. Both diffusive and nondiffusive (such as inertial) modes of relaxation of ions and solvent molecules are included in the theory. Explicit results are obtained for the time dependence of ion–ion, ion–solvent, and solvent–solvent van Hove functions at zero and finite wave vectors for solutions of varying ion concentration and dipolar strength. Frequency- and wave vector-dependent dynamic response functions of electrolyte solutions are also calculated by employing linear response theory. It is found that the dynamic response of ions and solvent molecules at finite wave vectors can be very different from that at zero wave vector (or at long wavelength). An application of the theory developed in this work is also discussed, where we have investigated the dynamics of ion solvation in electrolyte solutions by employing the frequency- and wave vector-dependent dynamic response functions.

Fluorescent Probes as Tools in In Vitro Toxicology

A number of different endpoints reflecting cell viability are commonly used to assess cytotoxicity. These endpoints are then taken to reflect cell death. It is not possible to elucidate the basis of the toxic mechanisms involved in these tests. However, by using a number of different endpoints to monitor different cellular events, the information that can be obtained from in vitro toxicity tests could be increased. Fluorescent probes appear to be promising alternatives for assessing cytotoxicity, and such probes are available for a number of different cellular events. In addition to viability, more-specific cellular events can be monitored, including intracellular glutathione levels, mitochondrial membrane potentials and intracellular concentrations of various ions. The possibility of using several fluorescent probes simultaneously, and hence of making measurements of several different cellular events at the same time, further increases the usefulness of fluorescent probes.

Wet deposition at the sub-20 km scale in a rural upland area of England

A network of 10 bulk precipitation collectors was established in an upland region of northern England to examine the small-scale variability of precipitation composition in a rural area. Significant spatial variability was shown for non sea-salt sulphate, calcium and hydrogen ion concentrations. Although nitrate concentrations did not show significant variability, a coherent gradient across the study area was observed. The large variability of calcium ion concentration across the area was related to limestone quarrying, which is prevalent in the south of the study area. Calcareous wind-blown soil may have also made a minor contribution to the abundance of calcium in the rain-water samples. It is likely, however, that a large fraction of the calcium was dry deposited to the funnels of the collectors in the form of particles. The network was not designed to study orographic enhancement of deposition, but it is suggested that this mechanism, along with wind-drift of scavenged cap-cloud droplets, cannot explain the spatial variation in ion concentrations. It is speculated that the variability in non-sea-salt sulphate concentrations may also be partially explained by reaction of CaCO 3 particles deposited to the funnels of the collectors with SO 2. Critical load exceedances in terms of deposited acidity from non-sea-salt sulphate were calculated using different spatially resolved deposition data. A better estimate of deposition in the study area was achieved by combining rainfall concentration data from the national network with the 5 km rainfall field, than the current methodology used for mapping of U.K. deposition which utilises a 20 km rainfall field. However, 20 km is considered to be the minimum resolution at which a procedure for parameterising orographic enhancement can be incorporated. Deposition and critical load exceedances in 2005 were calculated using a long-range transport model and significant improvements in the protection of soils were predicted from the projected emissions reductions.

A theoretical interpretation of ion composition measured on board the 'Active' satellite in the European sector during April 10−12, 1990 geomagnetic storm

Abstract. Ion composition measurements on board the ACTIVE satellite during the recovery phase of a strong geomagnetic storm of 10-12 April 1990 revealed extremely high concentrations (up to 103 cm-3) of the NO+, O+2, N+2 molecular ions in the topside F2-region of the European high-latitude zone. Concentrations of O+, N+, He+, H+ light ions were slightly decreased relative to prestorm quite conditions. Theoretical calculations were used to analyze the observed variations in ion concentration. Increased neutral temperature and [O2], [N2] are shown to be the main reasons for the observed ion concentration variations.

The influence of meteorology on rime and snow chemistry at a mountaintop site in northern California

Samples of rime and snow were collected from 36 storm events during three winters at a high-elevation site in northern California. Trajectories for the 36 events were segregated into types characterized by either large zonal or large meridional extent. The hypothesis that events dominated by meridional flow (potentially bringing pollutants to the study site from pollutant source areas to the south) were associated with elevated ion concentrations in time was not substantiated. For both the combined 3-year period, and winter 1988–89 alone, Cl−, NO 3 − , SO 4 2− , and H+ concentrations in rime were greater generally than in snow, with the 3-year median concentrations for these ions ranging from 7 to 11 μeq L−1 in rime, vs. 2 to 8 μeq L−1 in snow. Intra-year variation in ion concentrations in rime was high during all three winters, with maximum concentrations during events in winter 1988–89 at least 16 times the magnitude of the minimum concentration for each ion.

An ice-core chemistry record from Snøfjellafonna, northwestern Spitsbergen

A 2.2 m deep pit and the top 42.5 m of an ice core recovered at Snøfjellafonna, northwestern Spitsbergen, were continuously analyzed for Na+, Cl−, NO3−, SO42− and pH. Seasonal variations in ionic concentrations seem to have remained in the pit and the core, in spite of the relatively severe summer melting. We dated the core by counting annual peaks of Na+ and made an adjustment with the use of a tritium peak in 1963 as a reference horizon. It turned out that the depth of 42.5 m went back to the early 1930s or late 1920s. The 60–70 year record of snow chemistry showed that the concentrations of both NO3− and SO42− had increased in the 1950s and had decreased in the late 1970s and the 1980s. The increase would be explained in terms of anthropogenic inputs from the industrial areas. The later decrease of the same ions may have been caused by a combination of the reduction of the atmospheric precursors due to pollution controls and the meltwater-associated processes.

An ice-core chemistry record from Snøfjellafonna, northwestern Spitsbergen

A 2.2 m deep pit and the top 42.5 m of an ice core recovered at Snøfjellafonna, northwestern Spitsbergen, were continuously analyzed for Na+, Cl−, NO3 −, SO4 2− and pH. Seasonal variations in ionic concentrations seem to have remained in the pit and the core, in spite of the relatively severe summer melting. We dated the core by counting annual peaks of Na+ and made an adjustment with the use of a tritium peak in 1963 as a reference horizon. It turned out that the depth of 42.5 m went back to the early 1930s or late 1920s. The 60–70 year record of snow chemistry showed that the concentrations of both NO3 − and SO4 2− had increased in the 1950s and had decreased in the late 1970s and the 1980s. The increase would be explained in terms of anthropogenic inputs from the industrial areas. The later decrease of the same ions may have been caused by a combination of the reduction of the atmospheric precursors due to pollution controls and the meltwater-associated processes.

Ionic control of sperm function.

Successful sperm function leads to fertilization. It is dependent on the extracellular environment, especially the array and concentration of various ions. Considerable evidence indicates that this is because of consequent effects on the intracellular ionic composition. Although both cations and anions undoubtedly play a role in a modulating sperm function, most of the evidence currently available concerns cations. Therefore, this review will concentrate on cations, focussing on Ca2+, Na+, K+ and H+. Their requirements for successful capacitation (mammalian sperm) and acrosomal exocytosis (both invertebrate and mammalian sperm) will be considered. In particular, the mechanisms which may control ion fluxes, leading to changes in the intracellular ionic composition and subsequently to changes in sperm functional potential, will be addressed.

Parameters influencing the rejection properties of FT30 membranes

In order to elucidate the rejection properties of FT30 membranes, reverse osmosis experiments were carried out with varying ion concentration (1–40 mol/m 3), ion composition, transmembrane pressure drop (1–3 MPa) and pH (4–10). As model solution for each experiment demineralized water was used containing known amounts of salts such as NaCl, NaNO 3, KCl, KNO 3, Na 2SO 4 and CaCl 2 either single or in combination. Some experiments were made with solutions containing compounds that cause fouling of the membrane such as Fe(OH) 3 or humic substances. Specific rejection and overall salt rejection were determined by measuring the ion concentrations and electrical conductivity in samples of the permeate and concentrate. The results showed an increase of rejection with transmembrane pressure drop and a decrease in rejection with increasing concentration, whereby the latter effect was more distinct in mixed salt solutions than in single salt solutions. Rejection of anions and cations increased with pH as the membrane charge became more negative. Multivalent ions were better rejected than univalent ions. Nitrate was better rejected as single solute than in combination with other salts in solution. If fouling layers were formed on the membrane surface, the rejection properties changed. Fouling layers made of iron hydroxide caused a marginal decrease in salt rejection whereas fouling layers made of humic substances caused an improvement of salt rejection under the conditions used.

Radioactive aerosol charging with spatially varying ion concentrations

The bipolar ion production rate from β- or α-decays from a radioactive aerosol is not expected to be uniform in space, but to be concentrated close to aerosol particles. A charging theory is constructed which allows for this spatial dependence and contains ion recombination, radial ion diffusion and the aerosol attachment coefficients of Gunn ( J. Meteor. 11, 329 (1954)). The radial equations for the positive and negative ion concentrations are transformed into equations for the mean ion concentration and the net ionic charge which enables charge conservation to be treated explicitly. In the steady-state, the radial equations for the concentrations and the electric field are numerically solved iteratively to obtain the mean charge j on a radioactive aerosol. Results for j are obtained for wide ranges of aerosol concentrations and decay rates, and show very good agreement with values obtained assuming spatially uniform ion concentrations. The agreement, which arises in spite of large spatial variations in ion production rates, is attributed to the combination of radial ion diffusion and the ion recombination process.

Isotopic and ionic changes in a snow cover at different altitudes: observations at Austre Okstindbreen in 1991

Ionic and isotopic analyses of snow samples collected at four sites at the Norwegian glacier Austre Okstindbreen during two field seasons in 1991 showed that, before melting started, the snowpack was vertically inhomogeneous. Patterns of variation with depth of both ions and oxygen isotopes were maintained throughout the pre-melt period. Horizontal variations of ionic concentration were smaller than vertical ones. The stratigraphic pattern of ionic concentrations in the pack at lower altitudes reflected the influence of melting-refreezing processes, as well as original variations in the falling snow. The mean ionic content of the first set of samples collected at the lowest site was much lower than that at the others, indicating that ions had already been removed by meltwater. Much liquid water was present in the snowpack when drainage started, and ions were removed quickly with the first meltwater. During the melting phase, comparative rates of loss of ions resulting from differential movement through the pack were SO42−> Na+> Cl−. At 1475m, only 13% of the winter accumulation melted between 6 June and 9 July, but at least 88% of the Na+, 89% of the Cl−and about 100% of the SO42−was lost. Initially, there was no altitudinal trend in the mean δ18O values of the snowpack. Warming of the pack was accompanied by a tendency towards isotopic homogenisation. At the three sites at which snow remained in July, considerable18O enrichment had occurred since the middle of June.

Isotopic and ionic changes in a snow cover at different altitudes: observations at Austre Okstindbreen in 1991

Ionic and isotopic analyses of snow samples collected at four sites at the Norwegian glacier Austre Okstindbreen during two field seasons in 1991 showed that, before melting started, the snowpack was vertically inhomogeneous. Patterns of variation with depth of both ions and oxygen isotopes were maintained throughout the pre-melt period. Horizontal variations of ionic concentration were smaller than vertical ones. The stratigraphic pattern of ionic concentrations in the pack at lower altitudes reflected the influence of melting-refreezing processes, as well as original variations in the falling snow. The mean ionic content of the first set of samples collected at the lowest site was much lower than that at the others, indicating that ions had already been removed by meltwater. Much liquid water was present in the snowpack when drainage started, and ions were removed quickly with the first meltwater. During the melting phase, comparative rates of loss of ions resulting from differential movement through the pack were SO42− > Na+ > Cl−. At 1475m, only 13% of the winter accumulation melted between 6 June and 9 July, but at least 88% of the Na+, 89% of the Cl− and about 100% of the SO42− was lost. Initially, there was no altitudinal trend in the mean δ18O values of the snowpack. Warming of the pack was accompanied by a tendency towards isotopic homogenisation. At the three sites at which snow remained in July, considerable 18O enrichment had occurred since the middle of June.