Photochemistry of Ions at D-region Altitudes of the Ionosphere: A Review

The current state of knowledge of the D-region ion photochemistry is reviewed. Equations determining production rates of electrons and positive ions by photoionization of atmospheric neutral species are presented and briefly discussed. Considerable attention is given to the progress in the chemistry of O⁺(⁴S), O⁺(²D), O⁺(²P), N⁺, N₂ ⁺, O₂ ⁺, NO⁺, N₄ ⁺, O₄ ⁺, NO⁺(N₂), NO⁺(CO₂), NO⁺(CO₂)₂, NO⁺(H₂O) _n for n = 1–3, NO⁺(H₂O)(N₂), NO⁺(H₂O)₂(N₂), NO⁺(H₂O)(CO₂), NO⁺(H₂O)₂(CO₂), O₂ ⁺(H₂O), H₃O⁺(OH), H⁺(H₂O) _n for n = 1–8, O^?, O₂ ^?, O₃ ^?, O₄ ^?, OH^?, CO₃ ^?, CO₄ ^?, NO₂ ^?, NO₃ ^?, ONOO^?, Cl^?, Cl^?(H₂O), Cl^?(CO₂), HCO₃ ^?, CO₃ ^?(H₂O), CO₃ ^?(H₂O)₂, NO₃ ^?(H₂O), NO₃ ^?(H₂O)₂, OH^?(H₂O), and OH^?(H₂O)₂ ions. The analysis of the D-region rocket ion mass spectrometer measurements shows that, among these ions, O₂ ⁺, NO⁺, NO⁺(H₂O), and H⁺(H₂O) _n for n = 1–7 can make the main contribution to the total positive ion number density, and O^?, O₂ ^?, Cl^?, OH^?(H₂O), CO₃ ^?, HCO₃ ^?, NO₃ ^?, ONOO^?, CO₄ ^?, NO₃ ^?(H₂O), NO₃ ^?(H₂O)₂, and ³⁵Cl^?(CO₂) ions can be responsible for the main contribution to the total negative ion number density. Photodetachment of electrons from O^?, Cl^?, O₂ ^?, O₃ ^?, OH^?, NO₂ ^?, and NO₃ ^?, dissociative electron photodetachment of O₄ ^? and OH^?(H₂O), and photodissociation of O₃ ^?, O₄ ^?, CO₃ ^?, CO₄ ^?, ONOO^?, HCO₃ ^?, CO₃ ^?(H₂O), NO₃ ^?(H₂O), O₂ ⁺(H₂O), O₄ ⁺, N₄ ⁺, NO⁺(H₂O), NO⁺(H₂O)₂, H⁺(H₂O) _n for n = 2–4, NO⁺(N₂), and NO⁺(CO₂) are studied, and the photodetachment and photodissociation rate coefficients are calculated using the current state of knowledge on the cross sections of these processes and fluxes of solar radiation.     

Photodissociation rates in the atmosphere below 100km

In this survey we consider the atmospheric photodissociation rates of the molecules, O₂, O₃, NO, NO₂, N₂O, N₂O₅, HNO₃, HO₂, H₂O, H₂O₂, CO₂, CH₄, CH₂O, SO₂, and H₂S. Data for the absorption cross sections and quantum yields of these molecules are assembled here along with other information pertinent to the determination of photodissociation rates. The most recent techniques for computing atmospheric photodissociation rates are discussed. Photodissociation rates for all of the molecules are given at several solar zenith angles for altitudes up to 100 kilometres. A knowledge of the photodissociation rates of atmospheric molecules is essential to the resolution of many important atmospheric problems. Pollution of the stratosphere by high-flying aircraft, and of the troposphere by other anthropogenic activities, can only be described in terms of complex photochemical-dynamical models in which photolytic processes have a dominant role. A great deal of scientific effort is presently being spent in determining the mechanisms which control ozone, nitric oxide, and excited molecular oxygen concentrations in the mesosphere. Photolytic processes are already known to be important to all of these species. The photodissociation rates presented here can be applied directly to atmospheric problems such as these, or the methodology and data contained in this work can be used to compute photorates as needed.     

Ion Chemistry of the Ionosphere at E- and F-Region Altitudes: A Review

The current state of knowledge of E- and F-region ion chemistry is reviewed. Considerable attention is given to the progress in the chemistry of unexcited N₂ ⁺, O₂ ⁺, NO⁺, O⁺(⁴S), N⁺, H⁺, He⁺, Fe⁺, Mg⁺, Na⁺, Ca⁺, and K⁺ ions and electronically excited O⁺(²D), O⁺(²P), O⁺(⁴P), and $ {\text{O}}^{ + } (^{2} {\text{P}}^{*} ) $ ions. Achievements in our understanding of the role of vibrationally excited N₂ ⁺, O₂ ⁺, and NO⁺ ions in the ionosphere are discussed.     

Sulphur isotope equilibrium during sulphur hydrolysis at high temperatures

Studies of the sulphur hydrolysis reaction, 4S + 4H₂O /ag 3H₂S + HSO₄^? + H⁺, were conducted between 200 and 320°C in sealed silica glass tubes. The isotope exchange reaction: H₂¹⁸O + HS¹⁶O₄^? /ag H₂¹⁶O + HS¹⁸O₄^? is so rapid at the low pH (1.5–3) as to be unquenchable. However, the sulphur isotope exchange reaction: H₂³⁴S+ H³²SO₄^? /ag H₂³²S + H³⁴SO₄^? gave t12 values of 0.1, 0.3 and 1.7 days at 320, 260 and 200°C respectively and equilibrium H₂S - HSO₄^? sulphur isotope fractionation values of 20.9, 22.4, 24.8, 26.7 and 29.3‰ at 320, 290, 260, 230 and 200°C respectively. This latter data is represented by: 1000lnα_(HSO4^??H2S) = 5.07 (10⁶T^?2) + 6.33, and has valuable applications in geothermal and ore deposit studies.     

A numerical study of ionospheric profiles for mid-latitudes

This paper presents a numerical model and results for the mid-latitude ionospheric profile below the peak of the F₂-layer. The basis of the model is the solving of equations for four ionic species O⁺, NO⁺, O⁺₂ and N⁺₂, as well as the meta-stable O⁺(²D) and O⁺(²P). Diffusion and wind-induced drifts and 21 photo-chemical reactions are also taken into account. Neutral atmospheric density and temperature are derived from the MSIS86 model and solar extreme ultraviolate irradiance from the EUV91 model. In an effort to obtain a more realistic ionospheric profile, the key point at foF₂ and hmF₂ is fitted from the simulation to observations. The model also utilizes the vertical drifts derived from ionosonde data with the help of the Servo model. It is shown that the ionospheric height of peak can be reproduced more accurately under the derived vertical drifts from the Servo theory than with the HWM90 model. Results from the simulation are given for Wuchang (30.5°N, 114.4°E) and Wakkanai (45.6°N, 141.7°E), showing the profile changes with season and solar activity, and the E-F valley structure (the depth and the width). This simulation also reveals the importance of meta-stable ions and dynamical transport processes on the formation of the F₁-ledge and F₁-F₂ valley.     

The role of vibrationally excited nitrogen in the formation of the mid-latitude negative ionospheric storms

Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H⁺, O⁺(⁴S), O⁺(²D), O⁺(²P), NO⁺, O⁺₂ and N⁺₂ ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N₂ and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N₂] MSIS-86 decrease and vibrationally excited N₂ effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N₂ is brought about by the increase in the O⁺+N₂ rate factor.     

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

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.     

Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece

The chemical and isotopic compositions (δD_H2O, δ¹⁸O_H2O, δ¹⁸O_CO2, δ¹³C_CO2, δ³⁴S, and He/N₂ and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ¹⁸O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H₂–Ar, H₂–N₂, and H₂–H₂O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H₂O–H₂–CO₂–CO–CH₄ system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.     

Chemical Composition of Dew Resulting from Radiative Cooling at a Semi-arid Site in Agra, India

Dew samples were collected between October 2007 and February 2008 from a suburban site in Agra. pH, conductivity, major inorganic ions (F^?, Cl^?, NO ₃ ^? , SO ₄ ^2? , Na⁺, K⁺, Ca²⁺, Mg²⁺, and NH ₄ ⁺ ), and some trace metals (Cr, Sn, Zn, Pb, Cd, Ni, Mn, Fe, Si, Al, V, and Cu) were determined to study the chemistry of dew water. The mean pH was 7.3, and the samples exhibited high ionic concentrations. Dew chemistry suggested both natural and anthropogenic influences, with acidity being neutralized by atmospheric ammonia and soil constituents. Ion deposition flux varied from 0.25 to 3.0?neq?m^?2?s^?1, with maximum values for Ca²⁺ followed by NH ₄ ⁺ , Mg²⁺, SO ₄ ^2? , Cl^?, NO ₃ ^? , Na⁺, K⁺, and F^?. Concentrations of trace metals varied from 0.13 to 48?μg?l^?1 with maximum concentrations of Si and minimum concentration of Cd. Correlation analysis suggested their contributions from both crustal and anthropogenic sources.     

A numerical model of the ionosphere,including the E-region above EISCAT

It has been previously demonstrated that a two-ion (O⁺ and H⁺) 8-moment time-dependent fluid model was able to reproduce correctly the ionospheric structure in the altitude range probed by the EISCAT-VHF radar. In the present study, the model is extended down to the E-region where molecular ion chemistry (NO⁺ and O⁺₂, essentially) prevails over transport; EISCAT-UHF observations confirmed previous theoretical predictions that during events of intense E×B induced convection drifts, molecular ions (mainly NO⁺) predominate over O⁺ ions up to altitudes of 300 km. In addition to this extension of the model down to the E-region, the ionization and heating resulting from both solar insolation and particle precipitation is now taken into account in a consistent manner through a complete kinetic transport code. The effects of E×B induced convection drifts on the E- and F-region are presented: the balance between O⁺ and NO⁺ ions is drastically affected; the electric field acts to deplete the O⁺ ion concentration. The [NO⁺]/[O⁺] transition altitude varies from 190 km to 320 km as the perpendicular electric field increases from 0 to 100 mV m⁻¹. An interesting additional by-product of the model is that it also predicts the presence of a noticeable fraction of N⁺ ions in the topside ionosphere in good agreement with Retarding Ion Mass Spectrometer measurements onboard Dynamic Explorer.     

Fumarole/plume and diffuse CO2 emission from Sierra Negra caldera, Galapagos archipelago

Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO₂ emission of 11?±?2?t day^?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H₂S/SO₂, CO₂/SO₂, and H₂O/SO₂ molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H₂O, CO₂, and H₂S emission rates were 562, 394, and 3?t day^?1, respectively. The total output of diffuse CO₂ emissions from the summit of Sierra Negra volcano was 990?±?85?t day^?1, with 605?t day^?1 being released by a deep source. The diffuse-to-plume CO₂ emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H₂O; the main noncondensable components amounted to 97.4?mol% CO₂, 1.5?mol% SO₂, 0.6?mol% H₂S, and 0.35?mol%?N₂. The higher H₂S/SO₂ ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. ³He/⁴He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25?R _A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively.     

Time-dependent simulations of the global polar wind

It has been clearly established that there is a substantial outflow of ionospheric plasma from the Earth's ionosphere in both the northern and southern polar regions. The outflow consists of both light thermal ions (H⁺ and He⁺) and an array of energized ions (NO⁺, O₂⁺, N₂⁺, O⁺, N⁺, He⁺, and H⁺). If the outflow is driven by thermal pressure gradients in the ionosphere, the outflow is called the “classical” polar wind. On the other hand, if the outflow is driven by energization processes either in the auroral oval or at high altitudes in the polar cap, the outflow is called the “generalized” polar wind. In both cases, the field-aligned outflow occurs in conjunction with magnetospheric convection, which causes the plasma to drift into and out of the sunlit hemisphere, cusp, polar cap, nocturnal auroral oval, and main trough. Because the field-aligned and horizontal motion are both important, three-dimensional (3-D) time-dependent models of the ionosphere–polar wind system are needed to properly describe the flow. Also, as the plasma executes field-aligned and horizontal motion, charge exchange reactions of H⁺ and O⁺ with the background neutrals (H and O) act to produce low-energy neutrals that flow in all directions (the neutral polar wind). This review presents recent simulations of the “global” ionosphere–polar wind system, including the classical, generalized, and neutral polar winds. The emphasis is on displaying the 3-D and dynamical character of the polar wind.     

A discussion of the chemistry of some minor constituents in the stratosphere and troposphere

A discussion is given of atmospheric reactions in the H₂O–CH₄–O₂–O₃–NO _x system. In the lower troposphere such reactions may lead to significant production of ozone. Their role in the odd hydrogen balance, especially of the troposphere and lower stratosphere, is discussed. CH₃OH may be an intermediate in the oxidation cycle of methane, especially in the cold stratosphere. Its photodissociation into H₂ and CH₂O may consequently provide an important source for stratospheric H₂. Catalytic photochemical chains of reactions involving NO _x and HO _x may also lead to tropospheric destruction of ozone. Due to lack of knowledge it is not possible at present to evaluate the importance of the before-mentioned reactions.With the aid of model calculations it is indicated that stratospheric ozone is most sensitive to changes in the adopted lower boundary values of N₂O and that an increase in water vapour concentrations in the lower stratosphere will indeed cause some increase in ozone as predicted.Fluctuations in the flux of solar radiation near 190 nm may cause significant variations in stratospheric ozone concentrations.     

Subauroral red arcs as a conjugate phenomenon: comparison of OV1-10 satellite data with numerical calculations

This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15–17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He+ ions (three major ions: O⁺ H⁺ and He⁺ and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the diffusion of NO⁺ and O⁺₂ ions and O(¹D) and the revised electron cooling rates arising from their collisions with unexcited N₂, O₂ molecules and N₂ molecules at the first vibrational level. The updated model includes the option to use the models of the Boltzmann or non-Boltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the first five vibrational levels of N₂ were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N₂. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modeled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzm-ann vibrational distribution of N². The effect of using of the O(¹D) diffusion results in the decrease of 4–6% in the calculated integral intensity of the northern hemisphere and 7–13% in the calculated integral intensity of the southern hemisphere. It is found that the modeled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coefficients of O⁺(⁴S) ions with vibrationally excited nitrogen molecules and quenching of O⁺(²D) by atomic oxygen than the modeled intensities of the northern hemisphere.     

Negative ions in air-like gas mixtures

Summary The nature of negative ions in an air-like gas mixture containing 300 ppm²) of carbon dioxide and 1 ppm of water has been investigated using a drift tube working at atmospheric pressure and interfaced with a quadrupole mass spectrometer. It was found that the most dominant ion under equilibrium conditions is CO₄–·(H₂O).

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Zusammenfassung Mittels einer Kombination eines Beweglichkeits-Spektrometers und eines Vierpol-Massenspektrometers, ersteres im Bereich des normalen Luftdrucks arbeitend, wurde die Natur der negativen Ionen in einer luftähnlichen Gasmischung untersucht. Die Gasmischung enthielt 300 ppm²) Kohlendioxid und 1 ppm Wasserdampf. Es wurde festgestellt, dass unter Gleichgewichts-bedingungen das vorherrschende Ion die Formel CO₄–·(H₂O) hat.

     

Protonated Hydroxylamine-Assisted Iron Catalytic Activation of Persulfate for the Rapid Removal of Persistent Organics from Wastewater

This research aims at optimizing the effects of processing conditions, salts, natural organic materials, and water matrices quality on the effectiveness of the Fe(II)/K₂S₂O₈/hydroxylamine process in the degradation of pararosaniline. Assisting the Fe(II)/KPS (potassium persulfate) treatment with protonated hydroxylamine (H₃NOH⁺) increases the degradation rate of pararosaniline by more than 100%. Radical scavenger experiments show that the SO₄^●− radical dominates pararosaniline degradation in the Fe(II)/KPS system, whereas ^●OH is the dominant reactive species in the presence of H₃NOH⁺. The disparity in pararosaniline removal effectiveness upon the Fe(II)/KPS/H₃NOH⁺ and Fe(II)/KPS systems gets more significant with increasing reactants doses (i.e., H₃NOH⁺, H₂O₂, Fe(II)) and solution pH (2–7). Interestingly, H₃NOH⁺ increased the working pH to 6 instead of pH 4 for the Fe(II)/KPS process. Moreover, mineral anions such as Cl⁻, NO₃⁻, NO₂⁻, and SO₄⁻ (up to 10 × 10⁻³ m ) do not affect the efficiency of the Fe(II)/KPS/H₃NOH⁺ process. In contrast, acid humic decreases the performance of the process by ≈20%. In natural mineral water, treated wastewater, and river water samples, the Fe(II)/KPS/H₃NOH⁺ process maintains higher degradation performance (≈95%), whereas the process efficiency is greatly amortized in seawater. The efficiency of the Fe(II)/KPS process was drastically decreased in the various water matrices.     

A geostatistical approach for assessing population exposure to NO2 in a complex urban area (Beirut,Lebanon)

Few studies in the Middle East region estimated the spatial distribution of air pollutants for exposure studies. This paper presents a geostatistical approach to assess background NO₂ spatial distribution and the associated exposed population in a Mediterranean city with a complex topography, Beirut. Such modeling gave an accurate mapping of the 2010 yearly background average value of NO₂: it varies between 35 and 67 μg m^?3 with a mean of 53 μg m^?3. The mean SD of the estimated error was about 3 μg m^?3. The results showed that the spatial distribution of NO₂ follows a nested structuring, with a major structure related to topoclimatic characteristics (interaction topography/atmospheric flow at large scale) and a minor one linked to micro-environment and micro-climatic characteristics (interactions urban morphology/atmospheric flows at fine scale). The probability for the city’s inhabitants to be exposed to NO₂ levels exceeding 40 μg m^?3 threshold limit set by the World Health Organization (WHO) showed that Beirut city has a real sanitary risk to the NO₂ pollution. 93 % of the population (around 358,459 people) is 100 % sure to be exposed to a yearly average exceeding 40 μg m^?3. This knowledge will be certainly useful for developing a tool for decision support in order to implement policies of reducing air pollution in Beirut, which is, given the results, very urgent.     

Etude de la phase gazeuse occluse dans les laves de «l’Ardoukôba», volcan éphémère d’une dorsale émergée (Afar)

Gases trapped in lavas of three main flows of the Ardoukôba eruption (8 to 15 November, 1978) have been analysed by mass spectrometry. These analyses concern both plagioclase phenocrysts and microcrystalline mesostasis. Fluids are released between 500°C and 1200°C, and consist of H₂O, CO₂, CO, N₂, SO₂, HCl, H₂, CH₄ with traces of hydrocarbons and H₂S. The total content is less than 0.3–0.4 wt. % of samples with about 0.1–0.15 wt % of H₂O. No significant variation among the three flows is observed. Plagioclase phenocrysts are less abundant in fluids than the mesostasis (～2/3). The gases trapped in these phenocrysts are richer in CO and organic compounds, whereas mesostasis contain more H₂O, CO₂ and SO₂. CO is likely produced by reduction of CO₂ and H₂O with carbon during either analyses or eruption itself, or is of primary origin. In the latter case, gas composition suggests an entrapment temperature of about 1200°C ± 75°C. Kinetic study of the water and carbon dioxide release allows to calculate the diffusion characteristics of these fluids. Water and carbon dioxide behave rather similarly. Plagioclase gives a single activation energy value (8 Kcal/mole), while mesostasis gives two values (8 Kcal/mole, 15 Kcal/mole). Diffusion coefficients at 20°C are estimated to fall in the range 10^?13 · 10^?12 cm² · sec^?1.     

Dynamics of stream nitrate sources and flow pathways during stormflows on urban,forest and agricultural watersheds in central Pennsylvania,USA

Understanding the influence of storm events on nitrate (NO₃^?) dynamics is important for efficiently managing NO₃^? pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land‐use were established in Spring Creek, a 201 km² mixed land‐use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO₃^? (δ¹⁵N‐NO₃^? and δ¹⁸O‐NO₃^?) and water (δ¹⁸O‐H₂O) from baseflow to peakflow. Peakflow fractions of event NO₃^? and event water were then computed using two‐component mixing models to elucidate NO₃^? flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO₃^? sources and flow pathways. During small storms (<35 mm rainfall), greater event NO₃^? fractions than event water fractions indicated the prevalence of atmospheric NO₃^? source contributions at peakflow. During larger storms (>35 mm rainfall), event NO₃^? fractions were less than event water fractions at peakflow suggesting that NO₃^? was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash‐off of atmospheric NO₃^? was an important NO₃^? source at peakflow, especially during short‐duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO₃^? at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO₃^? sources into the stream, while deep soils in the karst lowlands also may have promoted NO₃^? assimilation. The results of this study illustrated how NO₃^? isotopes and δ¹⁸O‐H₂O could be combined to show key differences in water and NO₃^? delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

The solubility mechanisms of volatiles in silicate melts and their relations to crystal-andesite liquid equilibria

The anionic structure of magmatic liquids has been estimated at 1 atm and at pressures corresponding to those of the upper mantle. These estimates are based predominantly on spectroscopic data on binary metal oxide-silica and ternary metal oxide-silica-alumina melts. Structural information on melt compositions in aluminate-silica joins has been used to provide detailed information on the role of Al³⁺ in natural magma at atmospheric and high pressure.Regardless of pressure, andesitic melts may be described as combinations of chain, sheet, and three-dimensional network units. Nearly all Al³⁺ in the magmatic liquid resides in the three-dimensional network units. This Al³⁺ is locally charge-balanced with Na⁺, K⁺, Ca²⁺, and Mg²⁺. In the latter two cases, Al³⁺ and Si⁴⁺ are ordered, whereas for Na⁺ and K⁺, Si⁴⁺ and Al³⁺ are randomly mixed. Solution of water in natural magma results in the formation of new nonbridging oxygens in addition to OH groups attached to Si⁴⁺ and metal cations.On the basis of determined solution mechanisms of CO₂ and H₂O in silicate melts, thermodynamic properties of HO+CO₂, fluids and hydrous silicate melts and melting phase relations in peridotite-H₂O-CO₂, systems, it is found that natural andesitic magma in equilibrium with spinel Iherzolite in the upper mantle (10–20 kbar) must contain at least 5–7 wt.% H₂O. Andesitic magma with 5–7 wt.% H₂O in solution may be described as a mixture of Al-free three-dimensional units, sheets, and chains with a small proportion (less than 10%) of monomers.