Low Gas Concentrations Research Articles

Statistical modeling of the effects of wind speed, air temperature and relative humidity on the concentration of carbon monoxide in the urban atmosphere

The high carbon monoxide content in the urban atmosphere is one of the most important indicators of poor air quality in megacities such as Moscow. This study is to evaluate the importance of wind speed, air temperature, and relative air humidity for predicting the concentrations of carbon monoxide for the day ahead using a simplified one-dimensional quasistationary statistical model. It is shown that the concentration of carbon monoxide in the Moscow atmosphere is determined by a combination of internal (previous days CO concentration) and external (meteorological conditions) factors. The variation of carbon monoxide concentration at one station differs from the variation at another station due to the differences in local conditions. Taking into account wind speed and air temperature increases the predictive value of the onedimensional quasi-stationary statistical model for most of the stations. In contrast to wind, relative air humidity decreases the predictive value of the model for most of the stations. This means that meteorological factors considered in this study could have different effects on predicting carbon monoxide concentration in the case of Moscow. The data from the Balchug weather station, located in the city center, offers a more accurate CO concentration forecast for most Moscow stations compared to the VDNKh weather station. For a more complete description of the influence of meteorological conditions on the predicted low concentration of gases, it is useful to take into account the model wind direction, surface air pressure, and the intensity of mixing in the urban boundary layer.

The enhancement detection method based on the Fabry–Pérot cavity using terahertz frequency-domain spectroscopy

This article demonstrates a simple, efficient, and low-cost gas detection method for gases with absorption peaks in the terahertz range. A modes-adjustable Fabry–Pérot cavity is designed. By adjusting the length of the cavity, the center resonant frequency of the cavity can be coupled to the gas absorption peak. This kind of coupling can greatly enhance gas detection. To detect gas absorption peaks, we choose terahertz frequency domain spectroscopy (THz-FDS), whose frequency resolution can be up to the MHz level. Vapor is selected to verify the coupling phenomenon. The resonant frequency of the cavity is modified to couple to 0.56 THz, the absorption peak of vapor. Experiments are conducted at different humidity levels, the humidity is controlled by the supersaturated salt solution. Results indicate that at a humidity level of 15%, the coupling effect can enhance the detectability of vapor by approximately 167%, and this enhancement effect diminishes as humidity increases. We analyze the effect of different modes on the coupling and find that the high modes can make the coupling easier, but have little effect on the enhancement. Furthermore, the method is used to detect biomolecule-α-tyrosine to ensure it has wide applicability. This method can be used to detect substances with absorption peaks in the THz regime, especially for low-concentration gas.

A Comparative Review of Graphene and MXene-Based Composites towards Gas Sensing.

Graphene and MXenes have emerged as promising materials for gas sensing applications due to their unique properties and superior performance. This review focuses on the fabrication techniques, applications, and sensing mechanisms of graphene and MXene-based composites in gas sensing. Gas sensors are crucial in various fields, including healthcare, environmental monitoring, and industrial safety, for detecting and monitoring gases such as hydrogen sulfide (H2S), nitrogen dioxide (NO2), and ammonia (NH3). Conventional metal oxides like tin oxide (SnO2) and zinc oxide (ZnO) have been widely used, but graphene and MXenes offer enhanced sensitivity, selectivity, and response times. Graphene-based sensors can detect low concentrations of gases like H2S and NH3, while functionalization can improve their gas-specific selectivity. MXenes, a new class of two-dimensional materials, exhibit high electrical conductivity and tunable surface chemistry, making them suitable for selective and sensitive detection of various gases, including VOCs and humidity. Other materials, such as metal-organic frameworks (MOFs) and conducting polymers, have also shown potential in gas sensing applications, which may be doped into graphene and MXene layers to improve the sensitivity of the sensors.

A new experimental method to study the flame inhibition performance of low concentration halogenated gas

The minimum fire extinguishing concentration is a key index for the development of next generation chemical clean fire extinguishing gases, which is usually got by the cup-burner. The fire suppression performance of low concentration of chemical gas is hard to be understood by the available methods. In this work, the fundamental acknowledgement of steady flame surface attacking mechanism by halon functional group is newly discussed by conducting a series of bench scale tests with a cylindrical channel under a varied fluorinated gases. The characteristics of flame propagation under differentiated air atmosphere environmental conditions is obtained. The influence of fluorine-containing gas flow rate on flame propagation speed is clarified. A dimensionless relationship including atomic radius, bond length, polarization degree, molar mass and molar volume are proposed to describe the influence of low concentration of fluorine-containing gas on flame propagation speed. It provides an insight for the understanding of the flame inhibition performance of low concentration halogenated gas.

Optimization for hydrogen gas quantitative measurement using tunable diode laser absorption spectroscopy

Gas sensors are vital for safety, quality control, and environmental preservation across diverse industries. Tunable diode laser absorption spectroscopy (TDLAS) is widely employed for gas analysis due to its high sensitivity and selectivity. However, quantifying low concentrations of hydrogen gas using TDLAS in the infrared region proves challenging due to its lower absorption compared to other gases in the NIR region. This study introduces an innovative method for precise hydrogen gas measurement through the analysis of absorption spectra at different pressures and the employment of a high-pressure gas cell. By applying these methodologies to a calibration-free technique, we can realize the optimal measurement conditions for increasing the gas detection limit and stabilizing the wavelength lock for the laser diode. As a result, a linear relationship between hydrogen gas concentration and sensor response is achieved in the wide detection range of 0.01% to 100%. Under the optimal measurement conditions, our TDLAS system’s stability is demonstrated with minimum detection limits of 0.2866% and 0.0055% at integration times of 1 s and 30 s, respectively.

Thermal oxidation CuO nanowire gas sensor for ozone detection applications

In this study, cupric oxide nanowires (CuO NWs) on patterned interdigitated electrodes (PIEs) used as ozone (O3) gas sensors, were successfully fabricated using thermal oxidation and the microelectromechanical systems (MEMS) technique. After the thermal oxidation process, CuO NWs with different heights and densities were fabricated using a pure copper seed layer with a thickness ranging from 0.5 μm to 2 μm. In this experiment, a low temperature, low concentration, and repeatable CuO NWs gas sensor was fabricated, which can detect O3 gas at a low concentration of 50 ppb and low temperature of 100°C with a high sensor response (40%). The concentration response of this gas sensor shows an increasing linear trend, with an increase of O3 concentration in the range of 50 ppb - 300 ppb. Additionally, the results indicated that this CuO NWs gas sensor is more selective for O3 than CO, CO2, C2H5OH, C3H6O, NO2, or NH3. While CuO has been less studied in O3 detection compared with other semiconducting metal oxide materials, CuO NWs show potential applications in gas sensing devices for low-temperature and low-concentration O3 environmental monitoring.

Synthesis, characterization and sensing applications of TiO2 doped MOF composites for selective detection of ammonia at room temperature

Herein, we have developed a highly sensitive chemiresistive TiO2 doped metal–organic framework(MOF) composite-based sensor for ammonia detection at room temperature. Two novel Ti-MOFs@TiO2 composites are developed employing terephthalic acid and 2-amino terephthalic acid as organic linkers with Titanium tetra isopropoxide (TTIP) as a metal source by solvothermal technique. The morphology and crystallinity of synthesized compounds were characterized by using Field-emission scanning electron microscopy (FE-SEM) with EDX analysis, X-ray diffraction (PXRD), XPS and Brunauer–Emmett–Teller (BET) analysis techniques. MIL-125@TiO2 sensors exhibited a more specific surface area (374.74 m2 g−1) than the other three compounds. For gas-sensing applications, all composite materials were exposed to different gas vapours like ammonia, formaldehyde, acetic acid, ethyl alcohol, acetone, xylene, toluene and benzene at room temperature. The sensing results indicate that the sensors exhibit excellent response at low concentrations of ammonia, formaldehyde and acetic acid gases (1 ppm level). The enhanced sensor response was attributed to MIL-125@TiO2 (85 response at 50 ppm) and NH2-MIL-125@TiO2 (71 response at 50 ppm) towards ammonia gas and shows a better selectivity, sensitivity and repeatability to ammonia gas. All the materials exhibited less response times (between 8 and 45 sec) and more recovery times (between 13 and 125 sec).

Interface engineering of a 3D carbon nanofiber/iron oxide scaffold for room-temperature ethanol sensing

Ethanol is one of the most widely consumed chemicals and has high volatility. Long-term exposure to ethanol can cause irritation and damage to human organs and even lead to cancer. Therefore, reliable, low-cost and low-power ethanol gas sensors are urgently needed. However, due to the high barrier associated with the reaction between adsorbed oxygen and ethanol gas, current commonly used chemiresistive sensors are difficult to detect low concentration of ethanol gas at room temperature. Herein, we developed a 3D composite scaffold sensor, i.e. iron oxide nanoparticles decorated carbon nanofiber scaffolds (CNFs) from both the inside and outside (named Fe2O3@FCNFs) through interface engineering. The Fe2O3@FCNFs composite scaffold exhibited a 6-fold increase in specific surface area as compared to that of the FCNFs, and its carrier concentration of was one order higher than that of its counterpart. Therefore, the typical Fe2O3@FCNFs sensor exhibited an unanticipated good response to ethanol gas at room temperature, including high sensitivity (-6.268 % toward 100 ppm) and low limit of detection (10 ppm). This study provides an effective solution for preparing room-temperature chemiresistive ethanol gas sensors, which can be extended to other gas detection by tuning the semiconductor sensitive materials.

Extensive glacitectonism and rapid deglacial fluid expulsion in the northeastern Barents Sea

High-latitude regions store large amounts of carbon trapped by ice sheets, permafrost and gas hydrates, yet joint evolution of these climate components is poorly understood. Covered by a cold-based ice-sheet during the last glaciation, the seafloor of the northeastern Barents Sea reveals one of the largest known glacitectonic provinces in the Arctic. Up to 200-m high glacitectonic landforms are cratered and overlie faults associated with ‘bright spots’ indicative of subsurface gas accumulations. However, sediment samples show low pore gas concentrations and no present-day gas seepage. We combine new observations and ice-sheet - hydrate modelling to propose that during the Late Weichselian, glacitectonism was caused by patchy substrate stiffening due to gradual growth of subglacial gas hydrates and permafrost. Ice decay led to rapid destabilisation and full drainage of shallow hydrate reservoirs and permafrost thaw, causing craterisation which was likely accompanied by large fluxes of carbon released into the water column. This study shows that these processes were more widespread across glaciated margins, also highlighting sensitivity and potential for abrupt changes of high-latitude carbon pools in response to complex interactions between the cryosphere, ocean, and solid earth.

Sub-ppm of toxic gases detection on Ag-doped WO3 nanosensor

AbstractRecent investigations reveal an increasing interest in detecting toxic substances that, if present in the environment at low concentrations, can cause serious health conditions. Moreover, some of these toxic substances can be found as gases in human breath due to disease. Nanomaterial-based sensors have emerged as a crucial area of research for this purpose. This study focuses on silver-doped tungsten oxide nanoparticles (Ag/WO3) as nanosensors capable of detecting trace amounts of toxic gases at room temperature. These gases include Hydrogen sulfide (H2S), as well as other toxic gases like acetone, Ammonia (NH3), Ethanol (C2H5OH), and Acetone ((CH3)2CO). The gas-sensing behavior of Ag/WO3 nanosensors was investigated at extremely low concentrations of these gases. X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were employed to analyze the material's structure and chemical state. The sensor exhibited sensitivity to gas concentrations as low as 0.25 ppm, with a robust response of up to 80%. Notably, it showed the highest selectivity toward H2S gas compared to ethanol, ammonia, and acetone. The sensor's performance was also evaluated under varying temperatures and humid conditions, demonstrating reliable responses at room temperature. Heron, the synthesis of Ag/WO3 sensors with excellent sensitivity at extremely low gas concentrations is reported, making this sensor a promising tool for detecting toxic gases that threaten human health. Furthermore, the potential implications of this research on human health are significant, as detecting low concentrations of these gases can be a potential tool for the diagnostic process as well as health and environmental monitoring.

Real-Time Monitoring of Toxic Gases using Artificial Neural Networks with SnO2-based Thick Film Gas Sensors

The present study aims to develop an advanced system for real-time identification and measurement of harmful gases using Pd-doped SnO2-based thick film gas sensors integrated with Artificial Neural Networks. These sensors, renowned for their exceptional sensitivity and selectivity, undergo testing in a meticulously controlled gas chamber environment. Here, gas concentrations, temperature, and humidity are meticulously controlled. The gas chamber setup allows for mixing gases like carbon monoxide, nitrogen dioxide, and sulfur dioxide with nitrogen gas to achieve desired concentrations ranging from to . Temperature is kept at and relative humidity is maintained between to . The sensitivity analysis of the sensor demonstrates its adeptness in detecting low concentrations of target gases, with sensitivity increasing as gas concentrations rise, also the selectivity assessments highlight their ability to accurately differentiate between target gases and common interferents, ensuring precise detection even in complex gas mixtures. Response time testing indicates rapid detection capabilities, crucial and useful for emergencies. The Artificial Neural Network model, trained via the backpropagation algorithm, demonstrates remarkable accuracy, precision, recall, and F1 scores in predicting gas concentrations. The findings indicate that this integrated system offers a reliable and efficient solution for toxic gas detection, with potential applications in industrial safety and environmental monitoring.

Numerical Study on the Local Aggregation of Helium Bubbles in Liquid Lithium and Its Thermal Analysis

Abstract Liquid lithium is widely regarded as an optimal cooling medium for space nuclear reactors due to its exceptional heat transfer properties and low density. However, the helium bubbles generated by liquid lithium under space irradiation pose significant hazards to the safe and stable operation of nuclear reactions. This study employs the COMSOL finite element software to construct the level-set two-phase flow models and bubble stream model separately to investigate the local accumulation of helium bubbles and the overall flow of low-concentration gas–liquid mixtures. The main focus is on examining the different distributions of multiple helium bubbles randomly generated in local liquid lithium and the influence of boundary conditions on their accumulation morphology, as well as the impact of low-concentration bubble stream on their overall heat transfer performance. Agglomerated bubbles with radii between 5 μm and 150 μm are classified into three categories based on local concentrations: circular (≤20.37%), irregular elongated (up to 30.44%), and banded (up to 36.31%).The interconnected banded bubbles can be up to 8 times larger than irregularly elongated ones, and they have a positive effect on the distribution of physical quantities and wall temperature perturbations in the pipeline. The increase in inlet velocity triggers bubble impacts and fragmentation, further reducing thermal resistance and enhancing heat transfer performance. When the bubble diameter is less than 15 μm and the bubble concentration is within 1%, the influence of the mixed flow on overall heat transfer is not significant. This study provides insights for manipulating bubble structure and guiding localized and comprehensive thermal analyses.

Progress and advancements of coal mine gas control and management for safe mining in China

Coal is a guarantee and ballast of China’s energy security, and the Chinese government strongly supports the development of the coal industry. The level of coal mine gas control and utilization in China has increased to a new level, which has effectively promoted the high-quality development of China’s coal industry. In this new situation, the future innovative development of China’s coal mine gas control is discussed in six directions: continuously promoting the construction of transparent mines, paying attention to the atypical coal and gas outburst disasters, disaster monitoring and early warning, precise development of coal mine gas, industrialization technology of low-concentration gas, and coal mine gas control under the dual-carbon target. This will continue to contribute to the high-quality development of China’s coal industry and promote green, low-carbon transformations, and high-quality development in the coal industry.

Full characterization and calibration of a transfer standard monitor for atmospheric radon measurements

Abstract. In this work, a full characterization of the new user-friendly version of the Atmospheric Radon MONitor (ARMON), used to measure very low activity concentrations of the radioactive radon gas in the outdoor atmosphere, is carried out. The ARMON is based on the electrostatic collection of 218Po+ particles on a semiconductor detector surface. A main advantage of this instrument is that it offers high-resolution alpha-energy spectra, which will allow us to separate radon progeny (210Po, 218Po, and 214Po). The monitor feature may also allow measurements of thoron (220Rn) by collection of 216Po+, although the instrument is not calibrated for this gas. In the paper, the physical principle; the hardware configuration; and the software development of the automatic and remotely controlled ARMON, conceived and constructed within the MAR2EA and the traceRadon projects, are described. The monitor efficiency and its linearity over a wide span of radon concentration activities have been evaluated and tested here using theoretical and experimental approaches. Finally, a complete budget analysis of the total uncertainty of the monitor was also achieved. Results from the application of a simplified theoretical approach show a detection efficiency for 218Po+ of about 0.0075 (Bq m−3)−1 s−1. The experimental approach, consisting of exposing the ARMON at controlled radon concentrations between a few hundreds to a few thousands of becquerels per cubic metre (Bq m−3), gives a detection efficiency for 218Po+ of 0.0057 ± 0.0002 (Bq m−3) s−1. This last value and its independence from the radon levels were also confirmed thanks to a new calibration method which allows us, using low-emanation sources, to obtain controlled radon levels of a few tens of becquerels per cubic metre (Bq m−3). The total uncertainty of the ARMON detection efficiency obtained for hourly radon concentrations above 5 Bq m−3 was lower than 10 % (k= 1). The characteristic limits of the ARMON – being those dependent on the presence of thoron in the sampled air – were also calculated. A detection limit of 0.132 Bq m−3 was estimated in the absence of thoron. At a typical thoron concentration at atmospheric sites of 0.017 min−1, the detection limit was calculated to be 0.3 Bq m−3, but this can be reduced if using a delay volume, obtaining a decision threshold of 0.0045 Bq m−3. Current results may allow us to confirm that the ARMON is suitable to measure low-level radon activity concentrations (1–100 Bq m−3) and to be used as a transfer standard to calibrate secondary atmospheric radon monitors.

Investigation on thermal annealing effect on the physical properties of CuO-SnO2:F sprayed thin films for NO2 gas sensor and solar cell simulation

Thin films, owing to their versatility, are extensively employed in various applications, including solar cells and gas detection. In this study, CuO-SnO2:F thin films were fabricated using spray method. The influence of annealing temperature on their properties was examined. X-ray diffraction analysis of post-annealing at 300 °C revealed the emergence of the Cu2O phase, which disappeared at higher annealing temperatures of 500 °C. Substantial improvements in structural, optical, and electrical characteristics were observed, with the optimized films exhibiting heightened responsiveness at low NO2 gas concentration (4 ppm). The optimum operating temperature was determined at 150 °C, demonstrating small response and recovery times, and good reproducibility. Furthermore, Silvaco TCAD simulation was employed to model CIGS (Copper Indium Gallium Selenide) solar cells incorporating CuO-SnO2:F thin films as a buffer layer, yielding an impressive efficiency of 15.31 %.

Research on Low Concentration Gas Catalytic Oxidation Power Generation System

In response to the difficulties in direct utilization of low concentration gas in coal mines and the slow development of industrial application of catalytic oxidation technology, a new mode of direct utilization of low concentration gas with a methane concentration of 1.0% in coal mines in catalytic oxidation gas turbine power generation is explored. And based on the development of a 30kW low concentration gas catalytic oxidation gas turbine power generation system, this paper introduces the design process of key equipment such as catalytic oxidation burners, low-temperature and low-pressure turbines, and countercurrent regenerators, providing a technical reference for the utilization of low concentration gas catalytic oxidation.

Recent Progress on Porous Carbons for Carbon Capture.

High emission of carbon dioxide (CO2) has caused CO2 levels to reach more than 400 ppm in air and led to a serious climate problem. In addition, in confined spaces such as submarines and aircraft, the CO2 concentration increase in the air caused by human respiration also affects human health. In order to protect the environment and human health, the search for high-performance adsorbents for carbon capture from high and low concentration gas is particularly important. Porous carbon materials, possessing the advantages of low cost and renewability, have set off a boom in the research of porous adsorbents, which have the opportunity to be utilized on a large scale for industrial carbon capture in the future. In this review, we summarize the recent research progress of porous carbons for carbon capture from flue gas and directly from air in the last five years, including activated carbon (AC), heteroatom-modified porous carbon, carbon molecular sieves (CMS), and other porous carbon materials, with a focus on the effects of temperature, water content, and gas flow rate of industrial flue gas on the performance of porous carbon adsorbents. We summarize the preparation strategies of various porous carbons and seek environmental friendly porous carbon materials preparation strategies under the premise of improving the CO2 adsorption capacity and selectivity of porous carbon adsorbents. Based on the effects of real industrial flue gas on adsorbents, we provide new ideas and evaluation methods for the development and preparation of porous carbon materials.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Ultrasensitive ion liquid-CNT vdW heterostructure interface via anion-cation pair switch for SO2 detection

Low dimensional van der Waals (vdW) interface shows great advantages for application in vapor detection, such as ultra-high sensitivity and excellent reversibility. However, detection of non-character REDOX capacity and low atmosphere concentration gas such as SO2 is more challengeable. Inspired by the high efficient gas adsorption performance and versatile ion pair combination of ionic liquids, we constructed a vdW heterostructure interface based polymeric ion liquid/SWCNT sensor with different ionic pairs for SO2 detection. Via the composites tuning of SWCNTs and poly(vinylbenzyl 3-ethylimidazolium)-based ionic liquids (PILs) modified with different anions of chloride (Cl-), boron tetrafluoride (BF4-), hexafluorophosphate (PF6-), and bis(trifluoromethanesulfonimide) ions (Tf2N-), stable vdW heterostructure interface was successfully constructed, as proved by SEM, FTIR, XPS and Raman spectra. Upon SO2 adsorption, the distance between the cation/anion was tuned at the heterostructure interface, which triggered great composite tightness changes and thus electrical signal changes of heterostructure interface due to the reversed electron transfer, proved by XPS, Raman spectra and dynamics simulations. Among the sensors composed of the different anions, PIL-BF4-SWCNT exhibited lowest detection limit 20.4 ppt for SO2, which is the best result ever reported. The sensor also show great selectivity, reversibility and stability, with 3.77% response for 512 ppt SO2 within 14 days. The new strategy will open a new way for selective, ultrasensitive and low power vapor detection in complex environment.

Active manipulation of the plasmonic induced asymmetric photonic spin Hall effect

The asymmetric photonic spin Hall effect (APSHE) induced by surface plasmon polaritons in a graphene-based structure is actively manipulated by external magnetic field and electric field. It is revealed that the spin-dependent splitting exhibits spatio-temporal asymmetric property due to the involvement of the anisotropic graphene. The peak of asymmetry degree in APSHE at the position of reflectance valley corresponds toward a smaller incident angle with the increase of magnetic field intensity or Fermi energy, which is attributed to the tunability of reflectance for the graphene-based structure. Based on the asymmetric splitting shift, a potential application is proposed for detecting low concentration gas molecules and the detection resolution can be dynamically tunable by changing the magnetic field intensity and Fermi energy. This study may provide a new reference in the fabrication of graphene-based plasmonic sensor devices.