Variation Of Surface Concentration Research Articles

Variations in Surface Concentrations and Total Column of CO2 and CH4 in the Central Part of the European Territory of Russia

Variations in Surface Concentrations and Total Column of CO2 and CH4 in the Central Part of the European Territory of Russia

Variations in Surface Concentrations and Total Column of CO<sub>2</sub> and CH<sub>4</sub> in the Central Part of the European Territory of Russia

The results of measurements of surface concentrations and the total column of atmospheric carbon dioxide and methane at Obninsk station by the method of IR spectroscopy are presented. The description of the MR-32/MGС equipment for monitoring the gaseous composition of the atmosphere is given. Interannual and seasonal variations and trends in surface concentrations of CO2 and CH4 for 1998-2021 and total column for 2015–2021are analyzed. According to the results of cross-correlation wavelet analysis, the phase of annual variations in the column-averaged CH4 concentrations is ahead of the phase of surface variations by 2–3 months, and the variations in column-averaged CO2 concentrations lag behind the phase of annual variations in surface values by 1–2 months. The minimum surface concentrations of methane in May-A-ugust coincide with the column-averaged concentrations, and for carbon dioxide in the same period they are lower by 20–30 ppm. In the winter months, the minimum surface concentrations of methane and carbon dioxide are higher than column-averaged values by 70–150 ppb and by 6–15 ppm consequently. The measurement results are compared with GOSAT and data from European ground stations.

Variations in Surface Concentration of Fine Particulate Matter in Central Regions of the European Part of Russia

The model estimation is presented for the impact of interaction between anthropogenic and biogenic emissions of trace gases and aerosols on the mass concentration of the fine fraction of particulate matter (PM2.5) in the central region of the European part of Russia. The numerical study is performed with the CHIMERE chemistry transport model taking into account the formation of secondary organic aerosol from the oxidation of semivolatile organic compounds. The simulation results are in agreement with data of PM2.5 measurements at the Mosekomonitoring stations in Moscow. It is shown that the anthropogenic-biogenic interaction results in the growth of PM2.5 concentration. Its relative value varies within the analyzed region from several percent to several tens of percent and leads to the considerable (by 1.5 times) increase in the number of episodes in which average daily PM2.5 concentration exceeds the maximum permissible concentration accepted in Russia. It is found that the revealed increase in the number of such episodes is mainly caused by the accelerated formation of biogenic secondary organic aerosol in the presence of anthropogenic air pollution which accounts (on average over the region and season) for ∼60% of its surface mass concentration.

Influence of wall shear stress and geometry on the lumen surface concentration of low density lipoprotein in a model abdominal aortic aneurysm

In this work, the correlation between the wall shear stress (WSS) and the surface concentration variation of low density lipoprotein (LDL) on the walls of an idealized abdominal aortic aneurysm (AAA) is explored. It is observed that on the walls of AAA, the WSS has a significant effect on the LDL deposition pattern and a region of low WSS does not always correspond to a locally high concentration of LDL. The correlation between the WSS and the LDL deposition is found to be linked to the local fluid-flow pattern. This is explained by conducting an analysis on simplified geometries using steady inflow conditions that produced a fluid-flow pattern similar to that in the original AAA under physiologically relevant pulsatile inflow conditions. Furthermore, the influence of geometric parameters, such as the height, the width, and the shape of the aneurysm, on the surface concentration of LDL is studied. The width of the aneurysm is found to have a strong influence on the variation of the LDL surface concentration.

Silver Nanocube and Nanobar Growth via Anisotropic Monomer Addition and Particle Attachment Processes.

Understanding the growth mechanism of noble metal nanocrystals during solution synthesis is of significant importance for shape and property control. However, much remains unknown about the growth pathways of metal nanoparticles due to the lack of direct observation. Using an in situ transmission electron microscopy technique, we directly observed Ag nanocube and nanobar growth in an aqueous solution through both classical monomer-by-monomer addition and nonclassical particle attachment processes. During the particle attachment process, Ag nanocubes and nanobars were formed via both oriented and nonoriented attachment. Our calculations, along with the dynamics of the observed attachment, showed that the van der Waals force overcomes hydrodynamic and friction forces and drives the particles toward each other at separations of 10-100 nm in our experiments. During classical growth, anisotropic growth was also revealed, and the resulting unsymmetrical shape constituted an intermediate state for Ag nanocube growth. We hypothesized that the temporary symmetry breaking resulted from different growth rates on (001) surfaces due to a local surface concentration variation caused by the imbalance between the consumption of Ag+ near the surface and the diffusion of Ag+ from the bulk to the surface.

Source Apportionment and Size Distribution of Aerosols at Lin'an Atmosphere Regional Background Station During Winter

Using a wide-range particle spectrometer (WPS), an environmental management system (EMS), KC-120H middle volume sampler, a 850 professional ion chromatography analyzer, and heat/light carbon analyzer (DRI2001A), we observed the number concentration of aerosols with sizes ranging from 10 nm to 10 μm, gas concentrations, and concentrations of PM2.5, water-soluble ions, OC, and EC in a Lin'an atmospheric background station from January 9 to 31, 2015. The positive matrix factorization (PMF) model was applied for source apportionment, and the size distribution and diurnal variations of emission sources were analyzed based on the meteorological data. The average aerosol concentration was 5062 cm-3·nm-1 and PM2.5 mass concentration was 123.6 μg·m-3. The average concentrations of NO3-, SO42-, and NH4+, the main water-soluble ions in PM2.5 were 19.2, 15.4, and 10.8 μg·m-3, which accounted for 37.9%, 30.4%, and 21.4% of total water-soluble ions, respectively. Theaverage concentrations of OC and EC were 24.4 μg·m-3 and 6.6 μg·m-3. Secondary aerosol formation, coal combustion, motor vehicle emissions, dust, andbiomass burning were the main sources of PM2.5 in Lin'an during winter with contributions of 42.3%, 21.4%, 17.1%, 8.7%, and 10.6%, respectively. Different sources had different aerosol number concentration distributions. The aerosol number concentration spectra of secondary sources, vehicle emissions, dust, and biomass burning followed unimodal-type distributions with peaks at 120, 50, 100, and 90 nm. Coal particle number concentration was a bimodal distribution which exhibited peak values at 25 nm and 100 nm (19842 cm-3·nm-1 and 18372 cm-3·nm-1, respectively). The spectra of surface concentrations of secondary sources, coal combustion, motor vehicle emissions, dust, and biomass burning followed a three-peak distribution. The peaks were at 650, 210, 160, 180, and 575 nm. The diurnal variations of particle number concentrations influenced by diurnal variations in the boundary layer and human activities were consistent with the variations in surface concentrations, which displayed bimodal-type distribution.

The influence of nonstoichiometry on electrical transport and ethanol sensing characteristics for nanocrystalline LaFexO3 − δ sensors

Nonstoichiometric nanocrystalline LaFexO3−δ(x=0.7/0.8/0.9/1.0/1.1/1.2/1.3) powers were prepared by sol–gel method with citric acid. Temperature dependence of resistance for LaFexO3−δ sensors fits best to Holsteins model of small polaron hopping conduction. The resistance is determined by the competition between electrical valence compensation and oxygen vacancy compensation. And at each fixed temperature, the resistance is decreased with the introduction of more Fe deficiency. XPS analysis on O1s and C1s spectra verifies the existence of La-carbonate on the surface. The variation of surface concentration of adsorbed oxygen and La-carbonate, atomic ratio of Fe4+/Fe3+ and Fe/La with x value are discussed in combination, which indicate that the release of electrons trapped by native active oxygen due to the decomposition of monodentate La-carbonate also makes contribution to the response of LaFexO3−δ sensors to ethanol, in addition to the major contribution from adsorbed oxygen species. The best sensing performance of nanocrystalline LaFe0.8O3−δ sensor is ascribed to its relatively large surface concentration of adsorbed oxygen species and monodantate La-carbonate.

Seasonal and diurnal patterns in the dispersion of SO2 from Mt. Nyiragongo

Mt. Nyiragongo is an active volcano located in the Democratic Republic of Congo, close to the border of Rwanda and about 15 km north of the city of Goma (∼ 1,000,000 inhabitants). Gases emitted from Nyiragongo might pose a persistent hazard to local inhabitants and the environment. While both ground- and satellite-based observations of the emissions exist, prior to this study, no detailed analysis of the dispersion of the emissions have been made. We have conducted a dispersion study, using a modelling system to determine the geographical distribution of SO2.A combination of a meteorological model (WRF), a Lagrangian particle dispersion model (FLEXPART-WRF) and flux data based on DOAS measurements from the NOVAC-network is used. Since observations can only be made during the day, we use random sampling of fluxes and ensemble modelling to estimate night-time emissions.Seasonal variations in the dispersion follows the migration of the Inter Tropical Convergence Zone. In June–August, the area with the highest surface concentrations is located to the northwest, and in December–February, to the southwest of the source. Diurnal variations in surface concentrations were determined by the development of the planetary boundary layer and the lake-/land breeze cycle around lake Kivu. Both processes contribute to low surface concentrations during the day and high concentrations during the night. However, the strong northerly trade winds in November–March weakened the lake breeze, contributing to higher daytime surface concentrations along the northern shore of Lake Kivu, including the city of Goma. For further analysis and measurements, it is important to include both seasonal and diurnal cycles in order to safely cover periods of high and potentially hazardous concentrations.

Synthesis and processing of ELISA polymer substitute: The influence of surface chemistry and morphology on detection sensitivity

Despite the known drawbacks of enzyme-linked immunosorbent assay (ELISA), one of the deficiencies that have relatively been ignored is the performance of ELISA substrate itself. Polystyrene (PS), as the cost effective material of choice for mass production of ELISA well-plates, has shown obvious lacks of suitable physical and chemical properties for protein attachment. The general concept of this work was to develop a potential substrate that can be suggested as a material of choice for production of a new generation of ELISA analytical kits. Spin-coated thin films of polymethyl methacrylate-co-methacrylic acid (PMMA-co-MAA) on silicon surfaces were designed and processed for detection of dengue virus. Coated surfaces of different molar ratios have been investigated as carboxyl-functionalized layers for obtaining platform for biomolecule immobilization with high level of protein activity. To improve the sensitivity of detection, we have used amine functional “spacers”, hexamethylenediamine (HMDA) and polyethyleneimine (PEI), which were covalently bonded to the surfaces of PMMA-co-MAA coatings. Results demonstrate that the variation of surface concentration of carboxyl groups of PMMA-co-MAA can be used to control the amine surface concentration after carbodiimide coupling with HMDA and PEI spacers. The presence of amine spacers increases hydrophilicity of the coatings and significantly impacts the polymer surface morphology. In particular, protein immobilization via amine-bearing spacers has been achieved in two effective steps: (1) carbodiimide bonding between amine spacer molecules and PMMA-co-MAA polymer coatings; and (2) covalent immobilization of antibody via glutaraldehyde reaction with amine groups from amine-treated surfaces. The application of PEI spacer in comparison to HMDA has shown much higher intensity of detection signal in ELISA experiment, indicating better immobilization efficiency and preservation of antibody activity upon attachment to the polymer surface.

Exploring Differences between Charge and Discharge of LiMn2O4/Li Half-cell with Dynamic Electrochemical Impedance Spectroscopy

The electrochemical impedance spectroscopy (EIS) of a lithium-ion battery is usually measured at open-circuit state under a constant state-of-charge (SOC). In this way, the differences between charge and discharge cannot be distinguished, because they both occur in one cycle of the alternating current. To explore the differences, in this study, we propose a new implementation method measuring the dynamic EIS (DEIS) of a LiMn2O4/Li half-cell (0.8 mAh) in the galvanostatic mode while the cell is under charging or discharging at a series of direct currents (DC). The results show the charge transfer resistance, Rct, decreases with the increased DC. Also, Rct during charging is usually smaller than that during discharging. The dependency of Rct on the DC can be explained according to the Butler-Volmer equation. The difference in Rct between charge and discharge, ΔRct, is ascribed to a significant surface concentration variation caused by the DC.

Experimental Characterization of Front Propagation by Marangoni Forces in Ultrathin Liquid Films

Italian physicist Carlo Marangoni published a treatise in 1865 which first described the spontaneous flow of a liquid film caused by gradients in surface t ension at a gas/liquid interface. Such gradients are established by variations in surface concentration of molecular species which lower the surface tension in proportion to the interface concentration. While the dynamics and power law behavior of the initial circular advancing front in surfactant coated films has been studied for about two decades, there has been relatively little work conducted on characterizing the fractal spreading patterns which develop behind this front. In this thesis, we examine the dynamics of front propagation and subsequent fractal evolution in ultrathin liquid films of glycerol driven to spread by concentration gradients in Aerosol OT, an insoluble anionic surfactant. We vary only the initial deposition volume and concentration while maintaining the initial liquid film thickness at 2.5 microns. Contrary to theoretical analyses in the literature, our results reveal that the coefficient and exponent characterizing the advance of both the first front as well as the following unstable front is not a constant depending only on geometry (i.e. rectilinear vs axisymmetric spreading) but varies with the initial surfactant concentration of the deposition volume. Furthermore, the overall speed of the fronts is observed to increase with ambient relative humidity, an effect we ascribe to a reduction in the viscosity of the glycerol film clue to absorption of water from the ambient atmosphere. Only in cases of relatively high humidity (higher than approximately 40% relative humidity) do we observe the formation of fractal patterns in the unstable front. Measurements of the fractal dimension yield values in the range 1.45-1.65. The largest values approximate those fractal dimensions observed in systems undergoing diffusion driven aggregation or viscous fingering, neither of which mechanism is pertinent to Marangoni flow.

Water column distribution and carbon isotopic signal of cholesterol, brassicasterol and particulate organic carbon in the Atlantic sector of the Southern Ocean

Abstract. The combination of concentrations and δ13C signatures of Particulate Organic Carbon (POC) and sterols provides a powerful approach to study ecological and environmental changes in both the modern and ancient ocean. We applied this tool to study the biogeochemical changes in the modern ocean water column during the BONUS-GoodHope survey (February–March 2008) from Cape Basin to the northern part of the Weddell Gyre. Cholesterol and brassicasterol were chosen as ideal biomarkers of the heterotrophic and autotrophic carbon pools, respectively, because of their ubiquitous and relatively refractory nature. We document depth distributions of concentrations (relative to bulk POC) and δ13C signatures of cholesterol and brassicasterol combined with CO2 aq. surface concentration variation. While the relationship between CO2 aq. and δ13C of bulk POC and biomarkers have been reported by others for the surface water, our data show that this persists in mesopelagic and deep waters, suggesting that δ13C signatures of certain biomarkers in the water column could be applied as proxies for surface water CO2 aq. We observed a general increase in sterol δ13C signatures with depth, which is likely related to a combination of particle size effects, selective feeding on larger cells by zooplankton, and growth rate related effects. Our data suggest a key role of zooplankton fecal aggregates in carbon export for this part of the Southern Ocean (SO). Additionally, in the southern part of the transect south of the Polar Front (PF), the release of sea-ice algae during the ice demise in the Seasonal Ice Zone (SIZ) is hypothesized to influence the isotopic signature of sterols in the open ocean. Overall, the combined use of δ13C values and concentrations measurements of both bulk organic C and specific sterols throughout the water column offers the promising potential to explore the recent history of plankton and the fate of organic matter in the SO.

동북아시아 대기오염물질의 이동 패턴에 따른 장거리 수송 특성 연구

This paper investigates the physical and chemical characteristics of long-range transport (LRT) process of air pollutants by employing the MM5-CMAQ and its comparison with local emission dominant (LED) case over northeast Asia. We first classified high air pollution days into LRT and LED cases based on the synoptic meteorological variables of vorticity and geostrophic wind speed/direction at a geopotential level of over 850hPa. LRT cases are further categorized into three types of transport patterns (LRT-I-III) according to the air mass pathways from source regions. LRT-I-III are originated from northern, central, and southern China, respectively, identified by back trajectory analysis. Three LRT-I-III groups have different and unique locations of high pressure and transport pathways. The chemical characteristics showed that the simulated spatial distributions varied in terms of locations of maximum concentrations and the temporal variation of surface concentrations. The primary air pollutants such as , and of all of three LRT cases are well transported into Korea peninsula with different concentration levels. Of LRT cases, LRT-II has the greatest effect on air quality of Korea peninsula, followed by LRT-I and LRT-III. In comparison with LRT, the LED case shows relatively higher air pollution concentrations in general, but showed a variety of different air quality levels following the emission strength pattern. These widely varying patterns are impling the case dependent multi-directional approach for the development of indicators of long-range transport process over northeast Asia.

Hydrophobic droplets in amphiphilic bilayers: a coarse-grained mean-field theory study

Hydrophobic molecules such as oils and certain drugs can be encapsulated between the two leaflets of an amphiphilic bilayer in both lipid and polymer systems. We investigate the case where the hydrophobic molecules are incompatible with the amphiphile tails and so form droplets. Using a coarse-grained mean-field model (self-consistent field theory, or SCFT), we find that droplets of a wide range of sizes have the same characteristic lens shape, and explain this result in terms of simple capillarity arguments, consistent with the measured variations of surface concentrations of amphiphile in the bilayer and in the monolayers that cover the droplet. We study the effect of the strength chi_BO of the repulsion between the hydrophobic liquid and the amphiphile tails on the droplet shape, and find a gradual flattening of the droplet as chi_BO is reduced. The droplet remains at least metastable even at very low values of chi_BO. This is in contrast to the behavior as the length of the hydrophobic molecules is varied. Specifically, if these molecules are at least as long as the amphiphile tails, increasing their length further is found to have little effect on the droplet shape, while reducing their length below this value quickly causes the droplet to become unstable.

Co-located column and in situ measurements of CO<sub>2</sub> in the tropics compared with model simulations

Abstract. The first ground-based remote sensing measurements of the column averaged volume mixing ratio of CO2 (XCO2) in tropical South America have been obtained at Paramaribo, Suriname (5.8° N, 55.2° W). The remote sensing observations are complemented by surface air-samples collected at the site, analyzed for CO2 and 13CO2. The surface in-situ measurements are strongly influenced by local sources. From the isotopic composition of the air samples the local source component is suggested to be dominated by the terrestrial biosphere. Using δ13C from the NOAA/ESRL stations Ascension Is. (ASC), 7.9° S, 14.4° W, and Ragged Point (RPB), 13.2° N, 59.4° W, the data has been corrected for the local source component. Due to the migration of the Intertropical Convergence Zone (ITCZ) over the measurement site the sampled air masses belong to the Northern or Southern Hemisphere depending on the time of the year. Comparison to analyzed CO2 fields based on TM3 model simulations using optimized fluxes indicate agreement for the seasonality in XCO2 as well as for the corrected CO2 mixing ratios at the surface for the long dry season, when Paramaribo belongs to the Southern Hemisphere. A slightly worse agreement during the short dry season is attributed to a larger representation error during this time of the year. Overall the comparison indicates that the TM3 model is capable to simulate the seasonal variation of surface concentrations as well as column densities of CO2 correctly at Paramaribo. It has been also shown that the column measurements currently performed at Paramaribo have a limited precision and lack the link to the in situ measurements. Solutions for future improvements have been suggested.

Measurement of the surface concentration (liquid) of an evaporating multicomponent droplet using pendant droplet method

The surface concentration on the liquid side of the interface of an evaporating multicomponent droplet could be different from the bulk concentration. In this work, surface tension is used as a means to measure surface concentration of an evaporating multicomponent droplet. Surface tension is measured using pendant droplet method that relies on the best fit between theoretical and experimental drop profiles. Surface tension is a surface property, and it exhibits a dependence on concentration. Hence, it is an ideal candidate to track the variation of surface concentration during the evaporation of a multicomponent droplet. This method is used to study the evaporation of ethanol–water and methanol–water droplets. The correctness and applicability of this technique are critically assessed, and important observations are made for single droplet evaporation for these binary mixtures.

XPS and ToF-SIMS analysis of natural rubies and sapphires heat-treated in a reducing (5 mol% H 2/Ar) atmosphere

Surface effects on Mong Hsu rubies and Kanchanaburi sapphires after heat treatment in a controlled reducing atmosphere (5 mol% H 2/Ar) have been investigated using advanced surface science techniques including X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Visual appearance of the gemstones is clearly affected by the heat treatment in a reducing atmosphere. Kanchanaburi sapphires, in particular, exhibit Fe-containing precipitates after the heat treatment which have not been observed in previous studies under an inert atmosphere. Significant correlation between changes in visual appearance of the gemstones and variations in surface concentration of trace elements, especially Ti and Fe are observed. The XPS and ToF-SIMS results suggest that; (1) a reducing atmosphere affects the oxidation state of Fe; (2) dissociation of Fe–Ti interaction may occur during heat treatment.

Interfacial Dilatational Elasticity and Viscosity of β-Lactoglobulin at Air−Water Interface Using Pulsating Bubble Tensiometry

The ability of proteins to provide stability in foams is greatly influenced by their interfacial dilatational rheological properties. Surface tension response of a pulsatingbubble with an adsorbed layer of beta-lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. A methodology, accounting for adsorption/desorption as well as variation of surface concentration due to expansion/contraction, was developed for the evaluation of surface dilatational elasticity and viscosity at different frequencies from these measurements. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. The desorption rates were shown to be negligible for beta-lactoglobulin from the surface pressure response of a spread monolayer when subjected to compression in a Langmuir minitrough. The proposed model was employed to infer the interfacial dilatational viscosity and elasticity of an adsorbed beta-lactoglobulin layer at the air-water interface from experimental pulsating bubble data for protein concentrations in the range of 0.01-0.5 wt % at pH 7. As expected, the interfacial dilatational rheological properties were found to be higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. Heating at 80 degrees C for 30 min was found to result in higher interfacial dilatational viscosity and lower interfacial dilatational elasticity though this difference was within experimental error. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis.

Pulsed Current and Potential Response of Acid Copper System with Additives and the Double Layer Effect

A mathematical model for analyzing the double layer (dl) effect on pulse plating in the presence of additives is presented. Numerical simulations are employed to predict the influence of additives with various inclusion rates and capacities on current and potential response and mass transfer. It is shown that capacitive current density will not only increase in the presence of additives due to the increase in overpotential but also will increase with increasing dl capacity. Then, the variation of surface concentrations of additives and metal ions will even out as a result of the charging and discharging of the dl. The predicted results are compared with the experimental overpotential response on a copper rotating disk electrode in a bath containing 0.348 M and 2.06 M with and without 100 ppm polyethylene glycol. Good agreement between them is found. © 2002 The Electrochemical Society. All rights reserved.

Electrosorption of p-nitrobenzoic acid at a gold electrode in perchloric acid solutions studied by using cyclic voltammetry, EQCM, in situ FTIRS and Raman spectroscopy

Adsorption of p-nitrobenzoic acid (PNBA) at an Au electrode in 0.1 M HClO 4 solutions has been studied by combining cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), in situ Fourier transform infrared spectroscopy (FTIRS) and surface enhanced Raman spectroscopy (SERS). The adsorption of PNBA on Au electrode yields two current peaks appearing in the potential region between 0.3 and 1.0 V. A surface mass change of 74 ng cm −2 has been determined by EQCM, corresponds to the adsorption, which associates to a variation of surface concentration of 2.8×10 14 molecules cm −2. The spectral features observed from studies of in situ FTIRS and SERS illustrated, at molecular level, the potential-dependence properties of PNBA adsorption. The results demonstrated that the molecule of PNBA adsorbs in a flat mode at potentials below 0.3 V and that at higher potentials it trends to adsorb in a vertical adsorption mode via its carboxylic group towards Au electrode surface.