Coupled Gas Phase Research Articles

Janus Cobalt Sites on Carbon Nitride for Efficient Photocatalytic Overall Water Splitting

Regulating the dual active sites is crucial for enhancing the carrier-directed migration efficiency and shortening mass transfer distance of intermediates, particularly in photocatalytic overall water splitting. In this paper, we adopt in situ hydrothermal coupled gas phase chemical reduction methods to synthesize janus cobalt cocatalysts on g-C3N4. Experimental measurement and density functional theory calculations show that the janus cobalt cocatalysts fine-tunes the local electronic structure of g-C3N4, which can greatly reduce energy barriers and shorten mass transfer distance of intermediates for reactions. And while the built-in electric field of CoP and CoO also further efficiently facilitates rapid directional separation of interface carriers of the cocatalysts. This study elucidates atom-level mechanisms underlying overall water splitting and offers valuable insights for rational design of high-performance catalysts for overall water splitting. As a result, the CoP/CoO@g-C3N4 samples exhibit a remarkable enhancement in overall water splitting activity (133.2 μmol g−1 h−1 H2 and 67.2 μmol g−1 h−1 O2), surpassing that of the CoP@g-C3N4 and CoO@g-C3N4 samples by 1.4 and 3.8 times, respectively.

Multiple Promotional Effects of Vanadium Oxide on Boron Nitride for Oxidative Dehydrogenation of Propane.

Featuring high olefin selectivity, hexagonal boron nitride (h-BN) has emerged recently as an attractive catalyst for oxidative dehydrogenation of propane (ODHP). Herein, we report that dispersion of vanadium oxide onto BN facilitates the oxyfunctionalization of BN to generate more BOx active sites to catalyze ODHP via the Eley–Rideal mechanism and concurrently produce nitric oxide to initiate additional gas-phase radical chemistry and to introduce redox VOx sites to catalyze ODHP via the Mars–van Krevelen mechanism, all of which promote the catalytic performance of BN for ODHP. As a result, loading 0.5 wt % V onto BN has doubled the yield of light alkene (C2–C3) at 540–580 °C, and adding an appropriate concentration of NO in the reactants further enhances the catalytic performance. These results provide a potential strategy for developing efficient h-BN-based catalysts through coupling gas-phase and surface reactions for the ODHP process.

Experimental Investigation of Thermophysical Properties and Combustion Characteristics of Thickened Jet Fuel

ABSTRACT The thermophysical properties and combustion characteristics of PIB thickened jet fuel are investigated based upon both aims of expanding basic combustion theory (i.e., the coupled gas phase and liquid phase flows and heat transfer involving flame spread over liquid fuel) and potential practical applications (i.e., the oil additive in two-stroke gasoline engine and in-situ burning of leaked oils). The effects of PIB on the thermophysical parameters of jet fuel including density, flashpoint, viscosity and surface tension are experimentally measured. The logarithm of the dynamic viscosity varies linearly with the proportion of PIB, which is in good agreement with predictions. Then, the impact of PIB on fire safety of jet fuel is examined through flame spread and ignition experiments. The temperature evolution, flame spread rate, length and velocity of subsurface flow are quantitated and analyzed. The addition of PIB into jet fuel reduces the flame spread rate, but promotes the ignitability. The viscosity augment plays the principal role in hindering flame spreading over thickened jet fuel.

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900 °C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

Numerical investigation of droplet-droplet collisions in a water and milk spray with coupled heat and mass transfer

Large scale simulation models can aid in improving the design of spray dryers. In this work an Eulerian-Lagrangian model with coupled gas phase and droplet heat and mass transfer balances is used to study airflow dynamics, temperature and humidity profiles at different positions in the spray. The turbulent gas flow is solved using large eddy simulation (LES). A turbulent dispersion model accounts for the stochastic subgrid fluid velocity fluctuations along the droplet trajectory. The dispersed phase is treated with Lagrangian transport of droplets, and collisions between droplets which are detected with a stochastic Direct Simulation Monte Carlo (DSMC) method. The outcome of a binary collision is described by collision boundary models for water and milk concentrates. The drying of droplets is modeled by the reaction engineering approach (REA). The effect of the inlet air conditions and of droplet viscosity on the temperature and humidity distributions are analyzed. Most of the heat and mass transfer occurs in the first 10-20 cm from the nozzle where the slip velocities and temperature and humidity driving forces are higher. The droplets size increases, both in the axial and radial direction, because of the dominance of coalescence over separation in the droplet spray studied here. Because the spray domain considered in this work is relatively small, the droplet residence time is small, and consequently the amount of evaporation is still low. The droplet size distributions of milk concentrates are affected by the predominance of coalescence over separation events. The coalescence dominated regime increases when the droplet viscosity is higher.

Dithiocyanurates and thiocyamelurates: Thermal thiyl radical generators as flame retardants in polypropylene

A series of aliphatic and aromatic dithioethers of s-triazine and thioethers of s-heptazines were incorporated into polypropylene and their effectivity as flame retardants was analyzed using a limiting oxygen index (LOI) test, a DIN 4102-1 B2 test, thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and FTIR coupled gas phase analysis (EGA-FTIR). Four symmetric s-triazine disulfides of the type (RSS)3C3N3 - namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(octyldithio)- (8) and 2,4,6-tris(dodecyldithio)-1,3,5-triazine (10) - as well as five symmetric s-heptazine sulfides of the type (RS)3C6N7 - namely 2,5,8-tris(phenylthio)- (3), 2,5,8-tris(para-tolylthio)- (5), 2,5,8-tris(1,3-benzothioazol-2-yl)- (6), 2,5,8-tris(iso-propylthio)- (7) and 2,5,8-tris(octylthio)-s-heptazine (9) - were studied. The syntheses of 6, 7, 8 and 9 are reported for the first time. All compounds were analyzed by 1H and 13C NMR spectroscopy, FTIR and elemental analysis. The molecular structure of 7 was determined by single crystal XRD. Beside the flame retardant tests, the fluorescence of 3, 5 and 6 in powder form and when incorporated into polypropylene was measured.In the LOI test, the disulfides of s-triazine are more effective flame retardants than previously known organic disulfides studied in polypropylene.

Gas phase hydrotreatment of chlorophenols over Pd catalysts as an alternative route to cyclohexanone

We have established viability of cyclohexanone (C6ONE) production via coupled gas phase (1 atm, 423 K) continuous hydrodechlorination/hydrogenation of mono- and di-chlorophenols over bulk Pd and Pd/Al2O3. The catalysts have been characterised by temperature programmed reduction (TPR), H2 chemisorption, powder XRD and TEM analyses. Hydrodechlorination is not a thermodynamically limiting step where under catalytic control we achieve significantly greater C6ONE yields relative to those from standard phenol hydrogenation. We account for this response in terms of a direct chlorophenol → C6ONE conversion facilitated by electron delocalisation in the intermediate generated via electrophilic hydrogen cleavage of C–Cl bond(s). The C6ONE selectivity/conversion profiles coincided for bulk and supported Pd and we demonstrate structure sensitivity for the production of C6ONE from 2,4-dichlorophenol with higher specific rates over larger Pd particles (2 → 250 nm).

Detectability of deuterated water in prestellar cores

Water is an important molecule in the chemical and thermal balance of dense molecular gas, but knowing its history through-out the various stages of the star formation is a fundamental problem. Its molecular deuteration provides us with a crucial clue to its formation history. H$_2$O has recently been detected for the first time towards the prestellar core L1544 with the Herschel Space Observatory with a high spectral resolution (HIFI instrument). Prestellar cores provide the original reservoir of material from which future planetary systems are built, but few observational constraints exist on the formation of water and none on its deuteration before the collapse starts and a protostar forms at the centre. We report on new APEX observations of the ground state 1$_{0,1}$-0$_{0,0}$ HDO transition at 464 GHz towards the prestellar core L1544. The line is undetected, and we present an extensive study of the conditions for its detectability in cold and dense cloud cores. The water and deuterated water abundances have been estimated using an advanced chemical model simplified for the limited number of reactions or processes that are active in cold regions (< 15 K). We use the LIME radiative transfer code to compute the expected intensity and profile of both H$_2$O and HDO lines and compare them with the observations. We present several ad hoc profiles that best-fit the observations and compare the profiles with results from an astrochemical modelling, coupling gas phase and grain surface chemistry. Our comparison between observations, radiative transfer, and chemical modelling shows the limits of detectability for singly deuterated water, through the ground-state transitions 1$_{0,1}$-0$_{0,0}$ and 1$_{1,1}$-0$_{0,0}$ at 464.9 and 893.6 GHz, respectively, with both single-dish telescope and interferometric observations.

Assessing the kinetics of high temperature oxidation of Inconel 617 in a dedicated HTR impure helium facility coupling thermogravimetry and gas phase chromatography

A new facility coupling thermogravimetric analysis (TGA) with gas phase chromatography (GPC) has been developed. This facility is dedicated for studying high temperature oxidation of Inconel 617 in impure helium environment containing H2O, H2 and CO at very low partial pressures (in the Pa range), which is representative of the high temperature reactor (HTR) concept developed within the Generation IV Forum. Simultaneous acquisition of mass gain and gas composition has allowed the influence of carbon monoxide and water vapour on the kinetics of oxidation to be studied. GPC measurements of gas consumption have allowed the plotting of individual mass gain curves for oxidation by H2O and CO. During isothermal exposure at 1123K for 20h, the oxidation was mainly due to water vapour with a minor contribution of carbon monoxide during the first hours. The contribution of water vapour to the oxidation kinetics was extracted. It was shown to obey a complete parabolic law and to be limited by an interfacial reaction during the first few hours of oxidation and to be controlled by a mixed interfacial and diffusion process, diffusion becoming the rate-determining step for long term oxidation. There was very good agreement between GPC measurements and the experimental TGA results.

Coupling catalysis and gas phase electrocatalysis for the simultaneous production and separation of pure H2 and C2 hydrocarbons from methane and natural gas

This study reports the simultaneous production of pure H2 and C2 hydrocarbons (ethane and ethylene) in a solid oxide electrolysis cell coupled with an active catalyst powder bed. For first time, an Ag/YSZ/Ag double chamber cell was used and high yields to both, hydrogen and C2 hydrocarbons were achieved. The separately feeding of H2O and CH4 to the inner and outer chamber of the reactor, respectively, allows to obtain both kinds of products streams. Thus, steam was electrolyzed on the inner Ag electrode of the electrochemical cell (cathode), producing pure H2 (as the first product) and O2− ions, which were electrochemically supplied through the YSZ solid electrolyte to the outer Ag electrode (anode). On this latter, the reaction of the O2− ions and the oxygen evolved with the methane stream led to the production of C2 hydrocarbons (together with CO and CO2 as secondary combustion products). The C2s yield of this outer stream was strongly enhanced by the addition of an active catalyst powder bed (Ce–Na2WO4/SiO2 or Mn–Ce–Na2WO4/SiO2) to obtain the second product stream (with a high C2 yield up to 15%). The influence of the oxidative coupling catalyst powder bed, the reaction temperature and the gas phase composition was studied. Finally, the optimized system was studied by feeding a synthetic natural gas stream (instead of CH4) in order to approach to a more practical system. The high performance of the system was again verified along with a durability test under polarization conditions in view of the possible practical application of this novel reactor configuration system.

The role of surface species in chemical vapor deposited carbon nanotubes

Chemical vapor deposition (CVD) of carbon nanotubes (CNTs) has been investigated usinga coupled gas phase and surface chemistry model. This model successfully bridgedthe gap between the reactor and molecular length scales and allowed individualsurface kinetic processes to be identified as growth limiting directly from reactorscale parameters. Carbon nanotube growth rate is a function of the reactor walltemperature such that deposition would occur in the transition region between thehydrogen abstraction and hydrocarbon adsorption limited regimes. Deposition waslimited under low reactor temperatures or rich methane conditions by hydrogenabstraction from surface bound hydrocarbons due to the availability of gaseousH1. At high reactor temperatures and rich hydrogen conditions, the deposition reaction wasshown to be limited by hydrocarbon adsorption onto the nanoparticle surface. Optimalprocess conditions for efficient CNT production are discussed, as well as identifying thelimiting reaction steps for the surface chemistry.

A global model for C4F8 plasmas coupling gas phase and wall surface reaction kinetics

A global or zero-dimensional model for C4F8 plasmas is formulated by coupling gas phase and wall surface reaction kinetics. A set of surface reactions implements experimental findings and quantifies the effect of the fluorocarbon film formed on the reactor walls on the densities of species in the gas phase. The model allows the calculation of the pressure change after the ignition of the discharge and the effective sticking (surface loss) coefficients of the neutral species on the wall surface. The model is validated by comparison with experimental measurements, i.e. pressure rise and densities of F atoms, CF2 and CF radicals, in an inductively coupled plasma reactor. It is predicted that C4F8 is vastly dissociated and CF4 becomes the dominant species even at low power conditions. A net production of CF3 radical and a net consumption of CF2 radical at the reactor walls are predicted. A study on the contribution of each reaction to the production and consumption of the species shows that at least one surface reaction is among the major sinks or sources of CF4, CFx radicals and F.

Particle nucleation following the O3 and OH initiated oxidation of α‐pinene and β‐pinene between 278 and 320 K

Measurements of particle nucleation following the gas phase oxidation of α‐pinene and β‐pinene are reported. Particle nucleation following ozonolysis and O3 plus OH initiated monoterpene oxidation was measured in a 70‐L Teflon bag reactor over the temperature range 278 to 320 K. Particle concentration temporal profiles were measured for a range of initial monoterpene and ozone concentrations using ultrafine condensation particle counters. Profiles were interpreted using a coupled gas phase chemistry and kinetic multicomponent nucleation model to determine the molar yield of the nucleating species in the ozonolysis experiments to be 1 × 10−5 and 0.009, for α‐pinene and β‐pinene, respectively. OH initiated oxidation was found to increase the nucleator yield for α‐pinene, approximately a factor of three, but not for β‐pinene. The molar yield of condensable reaction products (vapor pressure &lt; 20 ppt at 296 K) was determined to be 0.06 for both α‐pinene and β‐pinene and was independent of the oxidation source. Particle growth, which is determined by the condensable reaction products, was nearly temperature independent. Atmospheric box model calculations of nucleation and particle growth for α‐pinene and β‐pinene oxidation under typical tropospheric conditions are presented and showed that (1) nucleation can be significant under favorable conditions, (2) nucleation is dominated by OH initiated oxidation, and (3) the partitioning of the condensable monoterpene oxidation products made a significant contribution to the growth of atmospheric aerosol and was capable of explaining the observed particle growth rates commonly observed in remote forests.

Technical note: A new comprehensive SCAVenging submodel for global atmospheric chemistry modelling

Abstract. We present the new scavenging scheme SCAV, simulating the removal of trace gases and aerosol particles by clouds and precipitation in global atmospheric chemistry models. The scheme is quite flexible and can be used for various purposes, e.g. long term chemistry simulations as well as detailed cloud and precipitation chemistry calculations. The presence of clouds can substantially change the chemical composition of the atmosphere. We present a new method of mechanistically coupling gas phase, aerosol, cloud and precipitation chemistry, which enables studies of feedbacks between multiphase chemistry and transport processes.

Effect of aerosol precursors from gas turbine engines on the volatile sulfate aerosols and ion clusters formation in aircraft plumes

A comprehensive analysis of the influence of sulfate aerosol precursor gases and chemi-ions generation in the internal flow of a jet engine (gas turbine engine) on sulfate volatile aerosols and ion cluster formation in an aircraft plume is presented. The evolution of the aerosol size distribution and the chemical composition change is simulated using a previously developed quasi one-dimensional flow field model with coupled gas phase kinetics, aerosol nucleation, condensation, and coagulation processes. An increased abundance of the aerosol precursors SO3, HSO3, and H2SO4 at the nozzle exit leads to an increased number of larger volatile aerosol particles, with diameter > 5 and 9 nm, than previously measured in aircraft exhaust plumes. Most of the gaseous H2SO4 gets converted to liquid aerosol particles within about 1 s. The generation of HSO4−, NO3−, NO+, and H3O+ ions in the combustor results in the formation of charged clusters, mostly HSO4−(H2SO4)m, NO3−(HNO3)(H2O), HSO4−(HNO3)n, H3O+(H2O)m, H3O+(CH2O)(H2O)n in the near field plume (first few hundred meters). For typical cruise conditions of a B-747 aircraft the calculated values of ion cluster concentration at the distance from nozzle exit L<40 m are around 3 × 105–3 × 106 cm−3 for fuel sulfur content (FSC≥0.04%) and only 7 × 104 cm−3 for free sulfur fuel (FSC=0%).

Fluid-solid coupling mathematical model of contaminant transport in unsaturated zone and its asymptotical solution

The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contaminant transport in unsaturated zone has been established based on fluid-solid interaction mechanics theory. The asymptotical solutions to the nonlinear coupling mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of pore pressure, pore water velocity and contaminant concentration in unsaturated zone has been presented under the conditions of with coupling and without coupling gas phase. An example problem was used to provide a quantitative verification and validation of the model. The asymptotical solution was compared with Faust model solution. The comparison results show reasonable agreement between asymptotical solution and Faust solution, and the gas effect and media deformation has a large impact on the contaminant transport. The theoretical basis is provided for forecasting contaminant transport and the determination of the relationship among pressure-saturation-permeability in laboratory.

Modeling cloud effects on hydrogen peroxide and methylhydroperoxide in the marine atmosphere

Hydrogen peroxide (H2O2) and methylhydroperoxide (CH3OOH) are studied with a coupled gas phase and aqueous phase chemical model representing a remote nonprecipitating cloudy boundary layer. Cloud interactions may deplete or enhance H2O2 but have a minor effect on CH3OOH. Therefore two primary questions are addressed: (1) do nonprecipitating clouds perturb the ratio of H2O2/CH3OOH, and if so, (2) what is the rate of reestablishment of this ratio to clear‐sky levels following cloud contact. The results show that the rate of recovery of the ratio of H2O2 to Ch3OOH after perturbation by cloud interactions depends on NOx (=NO + NO2) mixing ratios and on the time of day that cloud is encountered. When cloud contact is followed by a significant period of daylight, recovery to precloud values is rapid; however, when cloud contact occurs during the late afternoon or night, recovery can take up to 24 hours under high NOx conditions. Sensitivity tests show that in‐cloud heterogeneous conversion of HNO3 to aerosol has a small but detectable effect (∼10%) on the recovery of the ratio. Neglecting dry deposition of H2O2 and HNO3 increases the predicted ratio H2O2/CH3OOH in clear air prior to cloud contact, and has a small effect on the relative recovery rate of the ratio. In‐cloud consumption of H2O2 by SO2 suppresses the postcloud ratio by ∼40% relative to that in the base case for low levels of SO2 (∼200 ppt), with a more pronounced effect on the ratio and its rate of recovery for [SO2] ∼1 ppb. Because of the uncertainties associated with measurement of peroxides, and the dependence of the recovery of the ratio on the time of cloud contact, it is suggested that measurements of the ratio be considered judiciously and that they may not be of broad utility in predicting recent cloud contact.

Sulfur chemistry over the central Arctic Ocean during the summer: Gas‐to‐particle transformation

Atmospheric gas‐to‐particle transformation of the oxidation products of dimethyl sulfide (DMS) was investigated over the central Arctic Ocean by using observational data and a coupled gas phase chemistry‐aerosol dynamics model. Chemical compounds investigated were sulfuric acid (H2SO4(g)), methasulfonic acid (MSA(g)), and sulfur dioxide (SO2(g)) in the gas phase, and non‐sea‐salt sulfate (nss‐SO42−) and MSA in the particulate phase. During the advection from the open ocean to over the pack ice region, the particulate phase was found to be influenced significantly by three processes: (1) rapid removal of particulate matter during the first 1–2 days of advection, (2) continual formation of particulate nss‐SO42− and MSA, and (3) local production of particles consisting mostly of matter other than nss‐SO42− and MSA over the pack ice. In the absence of clouds and fogs, the principal sink for the vapors H2SO4(g) and MSA(g) were their condensational transport to submicron particles. SO2(g) was influenced significantly by both dry deposition and gas phase oxidation. Although there is a local source of coarse sea‐salt particles within the pack ice region, the role of these particles in the budgets of nss‐SO42− and SO2(g), and probably also in the budget of MSA, is only minor, especially when compared with marine regions at lower latitudes. The performance of the DMS gas‐phase chemistry scheme was tested against field data using a measurement case influenced minimally by clouds/fogs and the free troposphere. The predicted concentration of nss‐SO42− was within the uncertainties of the analysis, whereas that of MSA was high by a factor of 3–6. This demonstrates that not only heterogeneous reactions involved in atmospheric DMS chemistry but also certain gas‐phase reactions require further investigation.

Physico‐chemical modeling of the First Aerosol Characterization Experiment (ACE 1) Lagrangian B: 1. A moving column approach

During Lagrangian experiment B (LB in the following) of the First Aerosol Characterization Experiment (ACE 1), a clean maritime air mass was followed over a period of 28 hours. During that time span, the vertical distribution of aerosols and their gas phase precursors were characterized by a total of nine aircraft soundings which were performed during three research flights that followed the trajectory of a set of marked tetroons. The objective of this paper is to study the time evolution of gas phase photochemistry in this Lagrangian framework. A box model approach to the wind shear driven and vertically stratified boundary layer is questionable, since its basic assumption of instantaneous turbulent mixing of the entire air column is not satisfied here. To overcome this obstacle, a one‐dimensional Lagrangian boundary layer meteorological model with coupled gas phase photochemistry is used. To our knowledge, this is the first time that such a model is applied to a Lagrangian experiment and that enough measurements are available to fully constrain the simulations. A major part of this paper is devoted to the question of to what degree our model is able to reproduce the time evolution and the vertical distribution of the observed species. Comparison with observations of O3, OH, H2O2, CH3OOH, DMS, and CH3I, made on the nine Lagrangian aircraft soundings shows that this is in general the case, although the dynamical simulation started to deviate from the observations on the last Lagrangian flight. In agreement with experimental findings reported by Q. Wang et al. (unpublished manuscript, 1998b), generation of turbulence in the model appears to be most sensitive to the imposed sea surface temperature. Concerning the different modeled and observed chemical species, a number of conclusions are drawn: (1) Ozone, having a relatively long photochemical lifetime in the clean marine boundary layer, is found to be controlled by vertical transport processes, in particular synoptic‐scale subsidence or ascent. (2) Starting with initally constant vertical profiles, the model is able to “create” qualitatively the vertical structure of the observed peroxides. (3) OH concentrations are in agreement with observations, both on cloudy and noncloudy days. On the first flight, a layer of dry ozone rich air topped the boundary layer. The model predicts a minimum in OH and peroxides at that altitude consistent with observations. (4) Atmospheric DMS concentrations are modeled correctly only when using the Liss and Merlivat [1986] flux parameterization, the Wanninkhof [1992] flux parameterization giving values twice those observed. To arrive at this conclusion, OH is assumed to be the major DMS oxidant, but no assumptions about mixing heights or entrainment rates are necessary in this type of model. DMS seawater concentrations are constrained by observations.

Dust acoustic waves in strongly coupled dusty plasmas

Dust grains, or solid particles of \ensuremath{\mu}m to sub-\ensuremath{\mu}m sizes, are observed in various low-temperature laboratory plasmas such as process plasmas and dust plasma crystals. The massive dust grains are generally highly charged, and it has been shown within the context of standard plasma theory that their presence can lead to new low-frequency modes such as dust acoustic waves. In certain laboratory plasmas, however, the dust may be strongly coupled, as characterized by the condition ${\ensuremath{\Gamma}}_{d}{=Q}_{d}^{2}\mathrm{exp}(\ensuremath{-}d/{\ensuremath{\lambda}}_{D}{)/dT}_{d}g~1,$ where ${Q}_{d}$ is the dust charge, $d$ is the intergrain spacing, ${T}_{d}$ is the dust thermal energy, and ${\ensuremath{\lambda}}_{D}$ is the plasma screening length. This paper investigates the dispersion relation for dust acoustic waves in a strongly coupled dusty plasma comprised of strongly coupled negatively charged dust grains, and weakly correlated classical ions and electrons. The dust grains are assumed to interact via a (screened Coulomb) Yukawa potential. The strongly coupled gas phase (liquid phase) is considered, and a quasilocalized charge approximation scheme is used, generalized to take into account electron and/or ion screening of the dust grains. The scheme relates the small-$k$ dispersion to the total correlation energy of the system, which is obtained from the results of published numerical simulations. Some effects of collisions of charged particles with neutrals are taken into account. Applications to laboratory dusty plasmas are discussed.