Gas-phase Concentrations Research Articles

Ammonium nitrate evaporation and nitric acid condensation in DMT CCN counters

Abstract. The effect of inorganic semivolatile aerosol compounds on the cloud condensation nucleus (CCN) activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase. Two different questions were studied: (1) how big a fraction of semivolatiles is evaporated from particles after entering but before particle activation in the DMT-CCN counter? (2) How much can the CCN activity be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase? Both experimental and modelling results show that the evaporation of ammonia and nitric acid from ammonium nitrate particles causes a 10 to 15 nm decrease to the critical particle size in supersaturations between 0.1% and 0.7%. On the other hand, the modelling results also show that condensation of nitric acid or similar vapour can increase the CCN activity of nonvolatile aerosol particles, but a very high gas phase concentration (as compared to typical ambient conditions) would be needed. Overall, it is more likely that the CCN activity of semivolatile aerosol is underestimated than overestimated in the measurements conducted in ambient conditions.

Assessment of mass transfer correlations in rate-based modeling of a large-scale CO2 capture with MEA

A Rate-based simulation model was utilized for assessing the effect of correlations for mass transfer coefficients (kg, k1) and effective interfacial area (ae) on the performance of absorber for large-scale CO2 capture from a gas-fired power plant with a chemical solvent. The mass transfer and interfacial area correlations available in the literature are applied in the RateSep model to demonstrate the uncertainty associated with using these correlations in a large-scale CO2 capture plant. Selecting the best correlations for such a CO2 capture process is outside the scope of this work due to a lack of large-scale data for model validation. The absorption performance is expressed in terms of pressure drop per height of packing, gas and liquid phase temperature and concentration profiles, enhancement factor and necessary packing height. Variations in individual mass transfer coefficients, effective interfacial area, and overall mass transfer coefficient are also shown. The study showed that there is substantial uncertainty associated with applying the proposed correlations for determining the required absorber height. The variation in results, given as packing height needed for 90% CO2 removal, was very high, ranging from 6 to 24m. These are clearly too large discrepancies to be acceptable. The reason can, at least partly, be explained by the relationship between transport parameters, kinetics, mass transfer coefficients and effective interfacial area. Most packing mass transfer correlations available in the literature were developed and tested for specific packing types, specific chemical systems and mainly for distillation where the resistance lies mostly in the vapor phase. The best way to judge the correctness of these correlations for application in a large-scale CO2 capture processes with chemical solvents is to see how well the correlations predict reality, and validating the correlation's performance with pilot, or full scale data from CO2 capture with the same chemical solvent.

NO oxidation on plasma pretreated Pyrex: the case for a distribution of reactivity of adsorbed O atoms

The formation of NO2 molecules on a Pyrex surface, as a result of NO oxidation by adsorbed O atoms on the wall, is experimentally demonstrated and quantified. The measurements reveal that the characteristic times of heterogeneous NO2 production and NO gas phase decay change from ∼60 to ∼1500 s as the gas phase concentration of NO introduced in a tube pretreated with an oxygen radiofrequency discharge increases from 1013 to 1015 cm−3. Moreover, a clear variation of the characteristic loss frequency of NO molecules when small amounts of NO are successively injected in the tube is detected, between ∼7 × 10−2 and ∼5 × 10−3 s−1. The complex surface kinetics observed is studied and interpreted with the help of a mesoscopic surface model accounting for Eley–Rideal NO oxidation and slow NO2 adsorption, confirming the existence of adsorption sites possessing a distribution of reactivity on the surface.

Gas/solid particulate phthalic esters (PAEs) in Masson pine (Pinus massoniana L.) needles and rhizosphere surface soils

Phthalic acid esters (PAEs) are used in many branches of industry and are produced in huge amounts throughout the world. An investigation on particulate- and gas-phase distribution of PAEs has been conducted between January 2011 and December 2012 in Nanjing (China). Masson pine (Pinus massoniana L.) needles and rhizosphere surface soils were sampled from urban to suburban/remote sites, to investigate the pine needle/soil distribution of PAEs. The results showed that the average total PAE concentration (gas+particle) was 97.0ngm−3. The six PAE congeners considered predominantly existed in the gas phase and the average contribution of gas phase to total PAEs ranged from 75.0% to 89.1%. The PAE concentrations in rhizosphere soils and pine needles were positively correlated with their particulate- and gas-phase concentrations, respectively, which suggested that surface soils accumulated PAEs mainly through gravity deposition of particles and pine needle stomata absorbed PAEs mainly from the gas phase. The gas/particle partitioning (KP) and soil-pine needle ratio (Rs/n) were determined. Experimentally determined KP values correlated well with the subcooled liquid vapor pressures (PL). A set of interesting relationships of logRs/n−logKP−logPL was employed to explain the experimental findings of PAEs deposition to surface soils and to needles. This data set offered a unique perspective into the influence that Rs/n played in KP and correlated with PL.

Distribution of artificial sweeteners in dust and soil in China and their seasonal variations in the environment of Tianjin

A nationwide investigation on the occurrence of artificial sweeteners (ASs) was conducted by collecting 98 paired outdoor dust and soil samples from mainland China. The ASs were widely detected in Chinese atmospheric dry deposition and soil samples, at concentrations up to 6450 and 1280ng/g, respectively. To give a picture on AS distribution and source in the whole environment, the concentrations and seasonal variations of ASs in Tianjin were studied, including atmosphere, soil, and water samples. The AS levels were significantly higher in Haihe river at TJW (a sampling site in central city) in winter, while no obviously seasonal trends were obtained at BYL (close to a AS factory) and the site at a wastewater treatment plant. Saccharin, cyclamate, and acesulfame were the dominant ASs in both gas and particulate phase, with concentrations varying from 0.02 to 1940pg/m3. Generally, gas phase concentrations of the ASs were relatively higher in summer, while opposite results were acquired for particulate phase. Wet and dry deposition fluxes were calculated based on the measured AS levels. The results indicated that both wet and dry deposition could efficiently remove ASs in the atmosphere and act as important pollutant sources for the ASs in surface environment.

Quantitative Validation of the n-Butanol Sniffin' Sticks Threshold Pens.

Odorant pens are used by medical practitioners and researchers to assess olfactory dysfunction. Despite their routine use, there are currently no data on the gas-phase odorant concentrations released from the pen tips or whether these concentrations scale linearly with the aqueous-phase concentrations inside the pens. The commercially available Sniffin’ Sticks odor threshold test containing n-butanol was chosen for evaluation. The gas-phase concentration of n-butanol at the tip of each pen was measured directly in a new set of pens via proton-transfer-reaction mass spectrometry (PTR-MS). Measurements were additionally made on the same pens after 6 months and two older pen sets, namely a 3-year-old (used) and 4-year-old (new) set. Furthermore, application-related tests were made to determine the performance of the pens during routine use and under stress. These data demonstrate that the gas-phase n-butanol concentrations of the threshold pens are linear over the entire set, both for brand-new pens and 6 months later; this reflects the expected performance that was previously only assumed. Furthermore, the application–simulation tests demonstrated a good performance of the pens when used according to their intended protocol. Measurements of the older pen sets suggest that storage conditions are more critical than usage for pen stability. The present findings confirm that the n-butanol odorant pens are an appropriate tool for threshold testing, provided they are stored and handled correctly. Figureᅟ

CFD simulation of isothermal diesel oil hydrodesulfurization and hydrodearomatization in trickle bed reactor

The computational fluid dynamics (CFD) technique was used to study the effect of operational parameters on hydrodesulfurization (HDS) and hydrodearomatization (HDA) conversion in a trickle bed reactor (TBR). The Eulerian–Eulerian multiphase approach with appropriate momentum and mass interphase interactions models were implemented to describe reactor performance. The porosity distribution was considered to account wall effect on interphase interactions through the reactor. The simulations were performed at partially wetted bed at different operational conditions (temperatures, pressures, liquid and gas velocities as well as hydrogen sulfide concentration in gas phase) with proposing new reactions constant to remove reactions dependency from wetting effects. Furthermore, simulations were repeated at fully wetted bed to consider hydrotreating reactions conversion at fully wetted conditions. The effect of operational pressure on pressure drop through the bed and influence of liquid velocity on hydrodearomatization conversion were studied. Furthermore, temperature effect on mass fractions of species (desulfurized components, hydrogen and hydrogen sulfide) and reaction rate of HDS and HDA reactions were considered at both partially and fully wetted conditions. Finally, influence of bed porosity distribution was investigated on the local velocity, HDS reaction rate and hydrogen interphase mass transfer through the bed.

Boron Elimination Filter from SiH4 and B2H6 Gas Mixture for Purification of Metallurgical Si

We have proposed the solar-grade Si film formation method from metallurgical-grade (MG) Si source by using a chemical transport induced by high-pressure hydrogen plasma1). In this method, selectivity of hydrogen induced chemical reaction was utilized to eliminate the metal impurities from MG-Si source. However, MG-Si also contains B and P which are electrically active element in Si matrix. These are difficult to remove by using above method, because they can form volatile hydrides. So, the simple process to eliminate these elements is necessary. Fortunately, it can be expected that elimination of PH3 would be easily achieved by using a molecular sieve due to the polarity of PH3 2). However, B2H6 molecule has no dipole moment in common with SiH4, hence molecular sieve is not expected to remove B2H6 efficiently from SiH4 and B2H6gas mixture.Then, in this study, we have attempted to eliminate B2H6 from the gas mixtures by using difference of the pyrolytic behavior of both gases and demonstrated that the developed filter can operate effectively as B2H6filter. EXPERIMENTAL The porous carbon plate with its thickness of 5mm was used as filter element to the benefit of its chemical inertness, electrical conductivity (162μΩcm), relatively wide specific surface area, and its porosity (30%). The plate was settled in the filter vessel and connected to the heater power source to control its temperature by electrical heating. To investigate the elimination property of the pyloritic filter precisely, the SiH4 and B2H6 gases supplying from gas cylinder were used in this study. The gas mixture ratio of SiH4 and B2H6 was controlled through mass flow controller. Moreover, H2 and He are used as carrier gas. The transmission property of SiH4 and B2H6for porous carbon filter at various temperatures was evaluated by gas phase FTIR. To ensure the Boron elimination from Si material by using the filter, Si film was formed on Si substrate by thermal CVD at 800°C through the use of gas mixture after passing through the filter and B concentration in the film was evaluated by SIMS. RESULTS AND DISCUSSION Figure 1 shows the filter temperature (Tfilter) dependence of transmission properties of SiH4 and B2H6. He carrier gas flow rate was 10 slm. During the experiment, the filter vessel pressure was kept at 200 Torr. As shown in Fig.1, B2H6 transmittance begins to decrease at 200°C and is reduced to almost zero at 350°C. On the other hand, SiH4 begins to decrease at 450°C and shows the transmittance of 10% even at 550°C. From this result, it is found that B2H6 can be eliminated efficiently without sacrifice of SiH4, if the Tfilteris kept at 400°C.Figure 2 shows the B removal performance of the porous carbon filter at various temperatures. The carrier gas flow rate was 10slm. The removal performance (RPgas/film) was defined by dividing the concentration ratio in the gas phase(([B]/[Si])gas) by that in the Si film(([B]/[Si])film). The supplying concentration ratio in gas phase was 10-3 in this study. RPgas/film exponentially increases from 60 to 3200 with increasing the Tfilter from 300°C to 500°C. This temperature dependence of RPgas/film assures that the filter operates on the basis of difference of thermochemical decomposition between SiH4 and B2H6. CONCLUSION We have proposed and developed the B eliminating filter operating on the basis of difference of pyrolitic behavior between B2H6 and SiH4. B concentration in both gas phase and Si film could be decreased by filtering the gas mixture at the Tfilterof more than 300°C.REFERENCES1) H. Ohmi et al., Appl. Phys. Lett. 95(2009) 181506-1-3.2) A. Yusa et al., J. Electrochem. Soc. 122 (1975) 1700.

Correlating Ex-Situ and In Situ Measurement for Proton Exchange Membrane Fuel Cells

In the development of proton exchange membrane fuel cells (PEMFCs), the contamination effect on PEMFC durability can retard commercialization.1-4 To understand contamination mechanisms and their impacts on PEMFCs, experimental studies conducted and found the sensitivity of performance to the low levels of contamination. 1-9 Also, a simple isothermal model for contamination of a PEMFC which includes adsorption on the Pt catalyst, absorption into the membrane, and ion-exchange with ionomeric components was developed and presented. 8-9 In this paper, we discuss the relationship between ex-situ measurements using thin film electrodes and the in-situ performance of PEMFCs. The isotherms from ex-situ measurements for each mechanism provide a quantitative effect of coverage by contaminants and are shown to predict in-situvoltage losses when the proper dimensionless variables are used. For the Pt coverage the ex-situ measurements are performed on thin-film electrodes, which have typically lower Pt loadings (e.g., 0.02mg/cm2 vs. 0.4mg/cm2) and smaller geometric electrode areas (e.g., 0.24cm2 vs. 50cm2). As shown in Figure 1, these ex-situ Pt coverage data can be obtained with contaminants in the liquid phase. In contrast, for the in-situ performance, transport of contaminants can be through the gas phase. To establish the relationship between the coverage measured with ex-situ liquid concentration and the coverage corresponding to in-situ gas phase concentration, scaling techniques are required. Data are presented and discussed to test the scaling and the dimensionless groups. Acknowledgements The authors gratefully acknowledge support for this work by the DOE EERE Fuel Cell Technologies Office (DE-AC36- 08GO28308) under a subcontract from NREL (ZGB-0-99180- 1) to the University of South Carolina R eferences [1] R. Borup, J. Meyers, B. Pivovar, Y. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J. E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota , Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K. Kimijima and N. Iwashita, Chem. Rev. 107, 3904-3951, 2007.[2] K. O’Leary and B. Lakshmanan Paper #1036 presented at the 220th ECS Meeting & Electrochemical Energy Summit in Boston, MA, Oct. 13, 2011. [3] Proton Exchange Membrane Fuel Cell: Contamination and Mitigation Strategies edited by H. Li, S. Knights, Z. Shi, J. W. Van Zee, J. Zhang, p. 100, CRC press, New York, 2010.[4] J. St-Pierre, Air impurities: Polymer electrolyte fuel cell durability edited by F. Buchi, M. Inaba, T. J. Schmit, p. 289-321, Springer, New York, 2009.[5] H. N. Dinh, H. Wang, C. S. Macomber, K. O’Neil, and KC Neyerlin, Paper #34 presented at the 243rd ACS National Meeting, San Diego, CA 2012.[6] Md. Opu, M. Ohashi, H. Cho, C. S. Macomber, H. N. Dinh, J. W. Van Zee, ECS Trans. 50(2), 619-634 (2013).[7] H. Cho, Md. Opu, M. Ohashi, and J. W. Van Zee, Paper #1295, presented at the 222nd ECS Meeting & Honolulu PRiME 2012, HI, Oct. 09, 2012.[8] H. Cho and J. W. Van Zee, Paper #1260, presented at the 224th ECS Meeting 2013, San Francisco, CA, Oct. 27, 2013.[9] H. Cho and J. W. Van Zee, under review, Journal of the Electrochemical Society, 2013.

Improved Method for Measuring and Characterizing Phthalate Emissions from Building Materials and Its Application to Exposure Assessment

Phthalate emission from vinyl floorings was measured in specially designed stainless steel chambers. Phthalate concentrations increased and reached steady state after 2 to 5 days for all experiments. By having a high ratio of emission surface to sorption surface, avoiding mass loss of phthalates onto sampling pathways, and improving air mixing inside the chamber, the time to reach steady state was significantly reduced, compared to previous studies (1 to 5 months). An innovative approach was developed to determine y0, the gas-phase concentration of phthalates in equilibrium with the material phase, which is the key parameter controlling phthalate emissions. Target phthalate material-phase concentration (C0) and vapor pressure (Vp) were explicitly measured and found to have great influences on the y0 value. For low phthalate concentrations in materials, a simple partitioning mechanism may linearly relate y0 and C0, but cannot be evoked for high-weight phthalate percentages. In addition, the sorption kinetics and adsorption isotherm of phthalates on stainless steel chamber surfaces were determined experimentally. Independently measured or calculated parameters were used to validate a semivolatile organic compounds (SVOCs) emission model, with excellent agreement between model predictions and the observed chamber concentrations in gas and stainless steel phases. With the knowledge of y0 and emission mechanisms, human exposure to phthalates from tested floorings was assessed; the levels were comparable to previous studies. This work developed a rapid, novel method to measure phthalate emissions; emission measurement results can be connected to exposure assessment and help health professionals estimate screening-level exposures associated with SVOCs and conduct risk-based prioritization for SVOC chemicals of concern.

Correlation between catalytic activity and catalytic surface area of a Pt/Al2O3 DOC: An experimental and microkinetic modeling study

The readjustment of kinetic parameters in models of automotive catalytic converters due to catalyst aging calls for a better understanding of the correlation between model parameters and easily accessible quantitative catalyst properties. It is shown by means of CO light-off and CO chemisorption measurements that the catalytic activity of a commercial Pt/Al2O3 diesel oxidation catalyst can be successfully correlated to the catalytic surface area. This correlation exhibits the same trend for all investigated aging temperatures, aging times and lean aging atmospheres. However, no distinct correlation between catalytic activity and catalytic surface area is found for aging treatment in N2. The mechanism of noble metal sintering seems to depend on the oxygen content of the aging atmosphere and aging in N2 leads to a particle size distribution which is more beneficial to the catalyst activity, as compared to the particle sizes arising from lean aging conditions. This observation also implies that CO oxidation over platinum is structure sensitive. Furthermore, a refined microkinetic model for the platinum catalyzed oxidation of CO is developed which comprises two different paths for CO2 formation. The experimentally found correlation between catalytic activity and catalytic active surface area is successfully used for simulation of the activity change caused by lean hydrothermal aging. Spatially resolved gas phase concentration profiles of CO and CO2 during CO oxidation at full conversion are measured for further validation of the model.

Modeling the multiphase processing of an urban and a rural air mass with COSMO–MUSCAT

A reduced version of the complex aqueous phase mechanism CAPRAM3.0i (C3.0RED) was used in the regional chemistry transport model COSMO–MUSCAT in a 2-D application. Besides sulfate and nitrate production, the mechanism treats a complex HOx-chemistry, transition metal ion chemistry and organic species up to C4. The effects of the cloud chemistry on the chemical composition of air and particles were investigated. Sensitivity studies were conducted for an urban and a rural air mass. For this purpose simulations with C3.0RED were compared to ones with a simple inorganic aqueous phase mechanism (INORG) and without aqueous phase chemistry. A reduction of the gas phase concentrations of major oxidants was observed especially in the urban environment. Compared to INORG, C3.0RED is always more acidic leading to shifts in several chemical subsystems, (e.g. production of sulfate). Using C3.0RED instead of INORG, differences in sulfate mass of 3% to −15% occurred. The modeled O/C-ratio tends to be higher than observations as C3.0RED does not consider the whole population of organics and no insoluble organic mass. Nevertheless, the modeled concentration of glyoxalic acid is in the range of atmospheric measurements in both environments, whereas oxalic acid and pyruvic acid are underestimated in the urban case.

Composition and effects of inhalable size fractions of atmospheric aerosols in the polluted atmosphere: Part I. PAHs, PCBs and OCPs and the matrix chemical composition

Atmospheric particulate matter (PM) abundance, mass size distribution (MSD) and chemical composition are parameters relevant for human health effects. The MSD and phase state of semivolatile organic pollutants were determined at various polluted sites in addition to the PM composition and MSD. The distribution pattern of pollutants varied from side to side in correspondence to main particle sources and PM composition. Levels of particle-associated polycyclic aromatic hydrocarbons (PAHs) were 1-30ngm(-3) (corresponding to 15-35% of the total, i.e., gas and particulate phase concentrations), of polychlorinated biphenyls (PCBs) were 2-11pgm(-3) (4-26% of the total) and of DDT compounds were 2-12pgm(-3) (4-23% of the total). The PM associated amounts of other organochlorine pesticides were too low for quantification. The organics were preferentially found associated with particles <0.45μm of aerodynamic equivalent diameter. The mass fractions associated with sub-micrometer particles (PM0.95) were 73-90%, 34-71% and 36-81% for PAHs, PCBs and DDT compounds, respectively. The finest particles fraction had the highest aerosol surface concentration (6.3-29.7)×10(-6)cm(-1) (44-70% of the surface concentration of all size fractions). The data set was used to test gas-particle partitioning models for semivolatile organics for the first time in terms of the organics' MSD and size-dependent PM composition. The results of this study prove that at the various sites particles with diverse size, matrix composition, amount of contaminants and toxicological effects occur. Legislative regulation based on gravimetric determination of PM mass can clearly be insufficient for assessment.

Transported PDF modeling of pulverized coal jet flames

A transported composition probability density function (PDF) method is developed for pulverized coal combustion. A consistent hybrid Lagrangian particle/Eulerian mesh algorithm is used to solve the modeled PDF transport equation for the gas phase, with finite-rate gas-phase chemistry. The model includes k–ε turbulence, gradient transport for scalars, and a Euclidean minimum spanning tree (EMST) mixing model. A separate Lagrangian description is used to solve for the coal particle phase, including particle tracking, coal devolatilization and surface reaction models. Interphase coupling models are developed to handle the interaction between the gas phase and the solid phase. Radiative heat transfer is modeled by a P1 model for a gray absorbing emitting and scattering gas–particle system. Two independent laboratory-scale pulverized coal jet flames (“flame A” and “flame B”) are simulated using the new model. For flame A, the baseline model reproduces the measured mean and rms particle axial velocity reasonably well. Some discrepancies are found in particle temperature and gas-phase concentrations, which may in part be due to the uncertainties in the experimental data. Sensitivities of model results to coal-related model variations, turbulence–chemistry interactions, different interphase coupling strategies, and finite-rate chemistry are explored to establish sensitivities and to determine which aspects of the models are most important. The same model is applied to a second flame (flame B), the only change being in parameters related to the different coal composition. It is found that experimental standoff heights cannot be reproduced for three different stoichiometric ratios using a single model. Time scales for chemical reactions, devolatilization and turbulence are extracted and compared, to study the level of turbulence–chemistry–particle interactions in flame A and to test the popular assumption of equilibrium chemistry in coal combustion modeling. Mixture-fraction statistics for flame B are explored to test assumptions that have been proposed for mixture-fraction-based coal models. While the usual assumption of Beta distributions is found to be appropriate, assumptions of statistical independence of two mixture fractions are not valid.

A Modified Indigo Method for the Determination of Ozone in Nonaqueous Solvents

The indigo method for the analysis of aqueous ozone was modified to allow analysis of dissolved ozone in nonaqueous liquid phases. The method was tested using the solvent decamethylcyclopentasiloxane 245 and a vegetable oil. The molar absorptivity at 600 nm of the indigo trisulphonate molecule was re-checked and found to be 20,069 ± 412 L mol−1 cm−1 which is in agreement with the generally accepted value. Linear correlation between liquid phase and gas phase ozone concentrations confirmed that ozone solubility in decamethylcyclopentasiloxane 245 obeyed Henry's law with a constant of 1.71 ± 0.09 mg L−1 per mg L−1 in the gas phase. Ozone solubility in the vegetable oil followed a power law model with k = 0.148 and n = 0.767 (liquid and gas phase concentrations in mg L−1). The stoichiometry of the reaction between ozone in the nonaqueous phase and indigo trisulfonate in acidic solution was also confirmed as being about one. Moreover, the reaction products were confirmed by chromatographic analysis. This method was found effective to analyze ozone in nonaqueous solvents with a lower limit of detection of 2.6 μg L−1 and upper limit of detection of 142.7 mg L−1.

Study of Hydrate-Based Methane Separation from Coal-Bed Methane in Scale-up Equipment with Bubbling

In this work, orthogonal-test are introduced in small apparatus SHD-I with stirring and amplification experiments are carried out using scale-up equipment SHW-II with bubbling for hydrate-based CH4 separation from coal-bed methane gas. The optimal condition including 150ml THF-SDS solution, 1.50MPa and 277.15K are determined by orthogonal-test. Under the condition of 277.15K and 1.50MPa, the gas uptake with SHW-II is 165-fold enlarged comparing with that obtained in SHD-1. However, the amount of gas uptake per mole water, CH4 concentration in the residual gas phase and CH4 split fraction are nearly identical. It is testified that the scale-up equipment with bubbling is feasible as the enlargement equipment for CH4 recovery via hydrate-based separation method.

Theoretical investigation of structures and compositions of double neon-methane clathrate hydrates, depending on gas phase composition and pressure

The region of existence of neon clathrate hydrates is an actual problem of hydrate chemistry. The current work presents theoretical study of the equilibrium formation conditions of pure neon clathrate hydrates and double clathrate hydrates of neon-methane mixture. The structures and properties of double clathrate hydrates were described within the scope of the previously developed molecular clathrate hydrate model that takes into account the influence of guest molecules on the host lattice, interaction of guest molecules between themselves, and the possibility of multiple filling of host lattice cages by guest molecules. The model makes it possible to find an equilibrium state and thermodynamic properties of clathrate hydrates at given values of p and T. In the present work, we considered the properties of double clathrate hydrates in the range of pressures from 0 to 4 kbar at 250 K. The results of modeling have shown that the mass fraction of neon in double clathrate hydrate of Ne and CH4 mixture of cubic structure I (sI) can reach 26%, and 22.5% in double hydrate of cubic structure II (sII) even at a low methane concentration (1%) in gas phase, at high pressure. It is shown that in double clathrate hydrates of the Ne and CH4 mixture at high pressures, phase transition sII-sI can occur.

Model for acid-base chemistry in nanoparticle growth (MABNAG)

Abstract. Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapours condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapour pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapour pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3–20 nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 1010 cm−3 for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentrations of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e.g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organics and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.

Use of a Versatile High Efficiency Multiparallel Denuder for the Sampling of PAHs in Ambient Air: Gas and Particle Phase Concentrations, Particle Size Distribution and Artifact Formation

The design and performance of a multiparallel plate denuder able to operate at low and high-flow (3-30 L/min) for the collection of polycyclic aromatic hydrocarbon (PAH) vapor is described. The denuder, in combination with a micro orifice uniform deposit impactor (MOUDI) was used to assess processes of artifact formation in MOUDIs used with and without an upstream denuder. Duplicate sampling trains with an upstream denuder showed good repeatability of the measured gas and particle-phase concentrations and low breakthrough in the denuder (3.5-15%). The PAH size distributions within undenuded and denuded MOUDIs were studied. Use of the denuder altered the measured size distribution of PAHs toward smaller sizes, but both denuded and undenuded systems are subject to sampling artifacts.

Factors affecting the atmospheric occurrence and deposition of polychlorinated biphenyls in the Southern Ocean

Abstract. Persistent organic pollutants, such as polychlorinated biphenyls, reach the Southern Ocean atmosphere through long-range atmospheric transport. In this study we report the largest dataset available for the atmospheric occurrence of PCBs in the Southern Ocean surrounding the Antarctic Peninsula from samples obtained during three cruises in 2005, 2008 and 2009. The gas phase concentrations of total PCBs (Σ25PCBs) ranged from 1 to 70 pg m−3, while the aerosol phase concentrations were significantly lower (0.04 to 0.4 pg m−3). The aerosol phase is enriched in the more hydrophobic congeners consistent with the model predictions of gas-particle partitioning. There is a net air-to-water diffusive flux of PCBs to the Southern Ocean, up to 100 times higher than the dry deposition flux of aerosol-bound PCBs. The air-water disequilibrium is higher for the more hydrophobic congeners consistent with the role of the biological pump removing PCBs from the water column by settling of PCBs bound to organic matter. The atmospheric half-lives of PCB 52 and 180 are of 3.8 and 1 days, respectively, as calculated from the measured atmospheric concentration and depositional fluxes. The volatilization of PCBs from Antarctic soils during the austral summer drives higher gas phase concentrations in the atmosphere over Antarctica during the warmer periods. This temperature dependence is not observed for PCBs over the adjacent Southern Ocean, probably due to the importance of long-range atmospheric transport and atmospheric deposition modulating the atmospheric occurrence of PCBs.