Increasing Gas Concentrations Research Articles

LSTM based encoder-decoder for short-term predictions of gas concentration using multi-sensor fusion

Gas is one of the most dangerous byproducts of coal in mines. Before gas accidents occur, an abnormally increased gas concentration can be observed. Therefore, a prediction of the gas concentration in coal mines is of great significance to prevent the gas accident and ensure the production safety in the mines. By calculating the Pearson correlation coefficient for the gas concentration of different sensors, the spatial correlation of the gas concentration that is monitored for each mining face is verified. We present multi-step prediction results for gas concentration time series based on the ARMA model, the CHAOS model and the Encoder-Decoder model (single-sensor and multi-sensor) and compare these results. The Encoder-Decoder model provides high robustness in a multi-step prediction and can predict the gas concentration for five different time steps. Its prediction error is significantly lower than those of the ARMA and the CHAOS models. The prediction accuracy is further improved through a fusion with information of other sensors. In this way, this study provides a novel concept and method for gas accident prevention.

Projections of changes in marine environment in coastal China seas over the 21st century based on CMIP5 models

The increases of atmospheric carbon dioxide and other greenhouse gases have caused fundamental changes to the physical and biogeochemical properties of the oceans, and it will continue to occur in the foreseeable future. Based on the outputs of nine Earth System Models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), in this study, we provided a synoptic assessment of future changes in the sea surface temperature (SST), salinity, dissolved oxygen (DO), seawater pH, and marine net primary productivity (NPP) in the coastal China seas over the 21st century. The results show that the mid-high latitude areas of the coastal China seas (East China Seas (ECS), including the Bohai Sea, Yellow Sea, and East China Sea) will be simultaneously exposed to enhanced warming, deoxygenation, acidification, and decreasing NPP as a consequence of increasing greenhouse gas emissions. The magnitudes of the changes will increase as the greenhouse gas concentrations increase. Under the high emission scenario (Representative Concentration Pathway 8.5), the ECS will experience an SST increase of 3.24±1.23°C, a DO concentration decrease of 10.90±3.92 µmol/L (decrease of 6.3%), a pH decline of 0.36±0.02, and a NPP reduction of −17.7±6.2 mg/(m2·d) (decrease of 12.9%) relative to the current levels (1980–2005) by the end of this century. The co-occurrence of these changes and their cascade effects are expected to induce considerable biological and ecological responses, thereby making the ECS among the most vulnerable ocean areas to future climate change. Despite high uncertainties, our results have important implications for regional marine assessments.

Analysis of Precipitation and Temperature Variability over Central Africa (1901-2015)

Africa is already experiencing the impact of climate change. Some of the manifestations of climate change in Africa are, changing weather patterns resulting in, flooding and drought. Temperature change has impacted health, livelihoods, productivity of food, availability of water, and state of security. This study examines the long-term climate variations in Central African Countries (Gabon, Cameroon, Republic of Congo, Central Africa Republic, Chad and Democratic Republic of Congo) for the period 1901 to 2015, and then investigates the possible influence of increases in greenhouse gas concentrations. To investigate climate patterns and trends in the Central African Countries, precipitation and temperature were analyzed on annual time scales using data collected from the World Bank Group Climate Change Knowledge Portal. Data was further aggregated using annual average blocks of 10 years. Linear and polynomial regression was performed. Also, linear time series slopes were analyzed to investigate the spatial and temporal trends of climate variability in Central African countries. Results of the analyses indicated that the mean annual temperature and precipitation records in some of the Central African Countries had both warming and cooling trends over the study period from 1901 to 2015. For example, differences between the maximum and the minimum rainfall data for Democratic Republic of Congo, Cameroon and Gabon were 13 mm, 13 mm and 11.1 mm, which corresponded to 11.04%, 10.03% and 10.44% respectively. The study also found the temperature of Chad to have significantly risen from 1901 to 2015 by almost 20%, while its rainfall’s variation was limited. Although the variation in rainfall in Chad was not dramatic, the temperature per 10 year rose by almost 20%. Chad’s temperature rose according to a cubic model from about 24.5°C to just below 27°C during the period 1901-1940. This was followed by a brief drop between 1940 and 1960. From 1960 to 2015 it rose according to the model to almost 28°C. By 2040 the temperature is expected to reach about 29.5°C if this trend continues. Gabon was found to be the wettest country in Central Africa. Between 1901 and 1960, its average rainfall rose from about 144 mm to a maximum of approximately 160 mm. It had a general average rainfall/10 year’s increase from 1901 to 2015. The paper concludes by outlining policy recommendations in the form of improving national and regional environmental policies and regulations in the region, community involvement in decision making processes both at local and the national levels so as to contribute their input in the daily management of the forest resources, poverty alleviation in the region as well as building regional information system (RIS) incorporating Geographic Information System (GIS), remote sensing and other environmental and socio-economic data to help reduce anthropogenic emissions of greenhouse gases.

Distribution of methane and carbon dioxide concentrations in the near-surface zone over regional fault zones and their genetic characterization in the Pszczyna-Oświęcim area (SE part of the Upper Silesian Coal Basin, Poland)

The objective of this paper was to characterize the variability of methane (CH4) and carbon dioxide (CO2) concentrations in the near-surface zone, measured along 4 selected sampling lines positioned perpendicularly to regional fault zones, in the SE part of the Upper Silesian Coal Basin (USCB), Poland. This way it was possible to check the migration activity of these gases to the surface through low-permeable Miocene strata. It was also possible to evaluate the applicability of surface geochemical survey methodology to the identification of potential accumulations of free natural gas in the topmost parts of the Carboniferous formations in the USCB. The results of 319 soil-gas samples were supported by stable isotope analyses and related to the geological setting and the distribution of methane potential at various depths. Moreover, the sampling included the area of the closed and remediated Andrzej VII mining shaft, where 5 soil-gas samples were taken. Additionally, gas flux was evaluated at 3 measurement points at which increased gas concentrations were detected. The maximum concentrations of CH4 and CO2 in soil gases were 15.4 and 9.39 vol%, respectively. Soil gases contain both thermogenic and microbial CH4 and CO2 that migrated from secondary and primary gas zones within the Pennsylvanian coal-bearing strata. In some sites, CO2 was also generated by the oxidation of soil organic matter and/or CH4 in a near-surface zone. Anomalous CH4 concentrations were generally found over elevated fragments of erosional structures of Carboniferous coal-bearing formations. This indicates the presence of free CH4 accumulations beneath the Miocene overburden. However, the surface anomalies did not always correlate with the zones of CH4 secondary accumulations. Anomalous concentrations of CH4 and CO2 correlated with the regional fault zones that cut through the Carboniferous formations. This indicates the potential presence of fault traps saturated with free CH4 in the upper parts of Carboniferous formations. Relatively low values were observed for both CH4 and CO2 emissions (maximum: 25 and 4320 mg m−2 d−1, respectively). This suggests relatively low dynamics of gas migration from the depth to the soil zone.

Study of the impact of injection parameters on the performance of miscible sour gas injection for enhanced oil recovery

Sour gas reservoirs have faced critics for environmental concerns and hazards, necessitating a novel outlook to how the produced sour gases could be either utilized or carefully disposed. Over the years of research and practice, several methods of sour gas processing and utilization have been developed, from the solid storage of sulfur to reinjecting the sour gas into producing or depleted light oil reservoir for miscible flooding enhanced oil recovery. This paper seeks to investigate the impact of injection parameters on the performance of sour gas injection for enhance oil recovery. In designing a miscible gas flooding project, empirical correlations are used and the key parameter which impacts the phase behavior is identified to be the minimum miscibility pressure (MMP). A compositional simulator was utilized in this research work to study the effect of injection parameters such as minimum miscibility pressure, acid gas concentration, injection pressure and injection rate on the performance of miscible sour gas injection for enhanced oil recovery. The findings showed that methane concentration had a significant impact on the MMP of the process. Additionally, an increase in acid gas concentration decreases the MMP of the process as a result of an increase in gas viscosity, consequently extending the plateau period resulting in late gas breakthrough and increased overall recovery of the process.

Enhanced fluctuation for pinned surface nanobubbles.

By employing molecular dynamics simulations we investigate the fluctuation of surface nanobubbles immersed in liquid phase. Our simulation results indicate that in comparison with the surrounding liquid and nanobubble interior, the vapor-liquid or gas-liquid interface of nanobubbles always exhibits the largest compressibility, demonstrating the enhanced fluctuation for nanobubble interfaces. We also find that vapor surface nanobubbles and gas surface nanobubbles exhibit different fluctuation behaviors. For vapor nanobubbles that appear in overheated pure liquid, both density fluctuation and interface fluctuation are independent on the external pressure since the internal pressure remains constant at a given temperature. For gas nanobubbles that appear in gas supersaturated solution, the density fluctuation monotonously decreases with the increase of gas concentration, while the interface fluctuation shows a nonmonotonic variation. Departure from the intermediate gas concentration with the minimal interface fluctuation would enhance the fluctuation, which may finally lead to nanobubble destabilization. Finally, our simulation results indicate that the complicated interface fluctuation of surface nanobubbles comprises two different modes: interface deformation and interface oscillation, both of which display similar trends as that of the combined interface fluctuation.

Projected increase in the spatial extent of contiguous US summer heat waves and associated attributes

The frequency, intensity and duration of heat waves are all expected to increase as the climate warms in response to increasing greenhouse gas concentrations. The focus of this study is on another dimension of heat waves, their spatial extent, something that has not been studied systematically by researchers but has important implications for associated impacts. Of particular interest are spatially contiguous heat wave regions, examined here over the conterminous US for the May–September season in both the current climate and climate model projections from the CMIP5 archive (11 models total) using the RCP4.5 and RCP8.5 radiative forcing scenarios. Given their myriad impacts, heat waves are defined using multiple temperature variables, one which includes atmospheric moisture. In addition to their spatial extent, several other physical attributes are computed across contiguous heat wave regions, including a proxy for energy use. An estimate of the human population exposed to current and future heat waves is also evaluated. We find that historical climate model simulations, in aggregate, show good fidelity in capturing key characteristics of heat waves in the current climate while projections show a substantial increase in spatial extent and other attributes by mid-century under both scenarios, though generally less for RCP4.5, as expected. Overall, the study presents a framework for examining the behavior, and associated impacts, of a frequently overlooked aspect of heat waves. The projected increases in the spatial extent and other attributes of heat waves reported here provides a new perspective on some of the potential consequences of the continued increase in atmospheric greenhouse gas concentrations.

Assessment on the severity of low density polyethylene (LDPE)/Ethylene hybrid explosion

The potential explosion for low-density polyethylene (LDPE) dust is greatly increased due to the presence of ethylene gas. Thus, this study was aimed to investigate the explosion severity of polyethylene/ethylene hybrid mixture in a 20-L spherical vessel. The explosion setup is equipped with two chemical ignitors and Kistler piezoelectric pressure sensors to ignite the hybrid mixture and to quantify the propagation of pressure wave during the explosion process respectively. The following hybrid explosion characteristics including the maximum explosion overpressure (Pmax), the maximum rate of pressure rise (dP/dT) and deflagration index (KST) were evaluated. This study concluded that the explosion severity of polyethylene/ethylene hybrid mixture steeply increases as the gas concentration and particle size increase to 15 g/m3 and 125 μm, beyond which the Pmax and dP/dT steadily decrease. The highest Pmax and dP/dt were recorded at 5.5 bar and, 50.5 bar/s with the KST value is 50 bar.m/s indicating the LDPE/ethylene hybrid dust explosion possess a weak explosion.

Minimum explosion concentration of coal dusts in air with small amount of CH4/H2/CO under 10-kJ ignition energy conditions

A 20-L spherical explosion chamber was used to investigate the minimum explosion concentration (MEC) of coal dusts with small amount of flammable gas which is lower than its lower explosion limit (LEL). Two dust samples (anthracite coal and bituminous coal) and three flammable gases (CH4, H2 and CO) were tested. Two methods respectively based on overpressure and combustion duration time were used to determine the MEC of the hybrid mixtures. Experimental results show that the explosion of hybrid mixtures occurs when both dust and gas concentrations are lower than the LEL or MEC of the single substances. As flammable gas concentration increases, either explosion pressure (Pex) and explosion pressure rise (dp/dt)ex) increase or the MEC decreases for all the hybrid gas-dust mixtures as a general trend, showing a strong concentration effect. At the same concentration of coal dusts, the addition of CH4 poses a higher explosion risk than the other two flammable gases. Moreover, it was found that the results of MEC determined by both methods agree each other well, suggesting that both methods are valid to determine MEC of hybrid mixture in the synergic explosion region. The distribution of experimental data in the explosion regimes shows that the restricted areas defined by empirical formulas are insufficient from safety considerations.

Molecular Dynamics Simulation of Diffusion Behavior of CH4, CO2, and N2 in Mid-Rank Coal Vitrinite

The diffusion characteristics of CH4, CO2, and N2 in coal are important for the study of CO2-enhanced coalbed methane (CO2-ECBM) recovery, which has become the most potential method for carbon sequestration and natural gas recovery. However, quantitative research on the diffusion characteristics of CH4 and the invasive gases (CO2 and N2) in coal, especially those in micropores, still faces enormous challenges. In this paper, the self-, Maxwell’s, and transport diffusions of CO2, CH4, and N2 in mid-rank coal vitrinite (MRCV) macromolecules were simulated based on the molecular dynamics method. The effects of the gas concentration, temperature, and pressure on the diffusion coefficients were examined via the comparison of various ranks. The results indicated that the diffusion coefficients have the order of D(N2) > D(CO2) > D(CH4) in their saturated adsorption states. However, when MRCV adsorbed the same amounts of CH4, CO2, and N2, the self- and transport diffusion coefficients followed the order of DS(N2) > DS(CO2) > DS(CH4) and Dt(CO2) > Dt(N2) > Dt(CH4), respectively. Independent of the gas species, all these diffusion coefficients decreased with increasing gas concentration and increased with increasing temperature. In the saturated adsorption state, the diffusion activation energies of CH4, CO2, and N2 were ordered as CH4 (27.388 kJ/mol) > CO2 (11.832 kJ/mol) > N2 (10.396 kJ/mol), indicating that the diffusion processes of CO2 and N2 occur more easily than CH4. The increase of temperature was more conducive to the swelling equilibrium of coal. For the pressure dependence, the diffusion coefficients first increased until the peak pressure (3 MPa) and then decreased with increasing pressure. In contrast, the diffusion activation energy first decreased and then increased with increasing pressure, in which the peak pressure was also 3 MPa. The swelling rate changed more obviously in high-pressure conditions.

Tuning the detection limit in hybrid organic-inorganic materials for improving electrical performance of sensing devices

Research in hybrid electronics has included advances in materials, devices and architectures. However, in practice, controversy still exists on some details which limit hybrid materials to high-performance applications, such as processing–structure–design–property relations. This paper describes a practical approach to enhancing the sensing performance of a prototype ammonia gas sensor based on electrical conductivity changes, percolation theory and current limitation to a semiconducting polymer-metal oxide medium. This device is based on fully-gravure printed polyaniline/indium - tin oxide nanocomposites, Pani100−xITOx [0 ≤ x≤ 100% (wt/wt)], layers on a freestanding high-density polyethylene substrate. We find that the electrical current of the device decreases and tends to saturate as the gas concentration increases, and the value of this electrical current limit (IL) depends on x: the higher the value of x, the smaller the IL, when the current that flows through the electronic device was dominated by the ITO-nanoparticle filled PAni, which increase the concentration of hopping carriers and contribute to the desired electrical response of a heterogeneous gas sensor. In this regime, we find a good linear relationship between x and ammonia concentration. These findings suggest new directions for future research on the development and investigation of organic-inorganic devices in which the electrical current variation is desired for enhanced sensitivity and stability of hybrid sensors.

Econometric estimates of Earth’s transient climate sensitivity

How sensitive is Earth’s climate to a given increase in atmospheric greenhouse gas (GHG) concentrations? This long-standing question in climate science was recently analyzed by dynamic panel data methods using extensive spatio-temporal data of global surface temperatures, solar radiation, and GHG concentrations over the last half century to 2010 (Storelvmo et al, 2016). Those methods revealed that atmospheric aerosol effects masked approximately one-third of the continental warming due to increasing GHG concentrations over this period, thereby implying greater climate sensitivity to GHGs than previously thought. The present study provides regularity conditions and asymptotic theory justifying the use of time series cointegration-based methods of estimation when there are both stochastic process and deterministic trends in the global forcing variables, such as GHGs, and station-level trend effects from such sources as local aerosol pollutants. The asymptotics validate estimation and confidence interval construction for econometric measures of Earth’s transient climate sensitivity (TCS). The methods are applied to observational data and to data generated from several groups of global climate models (GCMs) that are sampled spatio-temporally and aggregated in the same way as the empirical observations for the time period 1964–2005. The findings indicate that 7 out of 9 of the GCM reported TCS values lie within the 95% empirical confidence interval computed econometrically from the GCM output. The analysis shows the potential of econometric methods to provide empirical estimates and confidence limits for TCS, to calibrate GCM simulation output against observational data in terms of the implied TCS estimates obtained via the econometric model, and to reveal the respective sensitivity parameters (GHG and non-GHG related) governing GCM temperature trends.

Sense trace gases based surface plasmon polarization waveguide of graphene

To improve the selectivity of carbon nanotubes for gas sensors, we design a surface plasmon polarization waveguide based on graphene that can sense trace gases. In addition, a gas concentration measurement system was designed for a sensor based on optical cavity ring-down spectroscopy. The gas concentration measurement system was composed of two loops, which were combined with the minimum mean square error algorithm to achieve an amplified spontaneous emission noise filter. The experimental results show that the gas concentration measurement error was significantly improved after CO filtering. The slope of the logarithmic ring-down curve and the ring-down time decreased with the increasing gas concentration. The gas concentration and ring-down time showed an improved linear relationship. The design system can detect trace gases as a single gas or a variety of toxic gases in special environments. The device provided a wide range of sensors and measurements. Moreover, the proposed device is relatively simple and easy to implement, with high detection sensitivity.

Agroforestry Land Use Systems for Climate Change Adaptation and Mitigation in Ethiopia: A Review

Deforestation and forest degradation are major contributors to recent increases in atmospheric greenhouse gas concentrations and changes to the world's hydrological cycle. For instance most of the European countries, the industrial process emissions are typically 1-2% of total emissions in the world. In Ethiopia, the current contribution is very low as compare to a global scale, but will more than double from 150 MtCO 2 e to 400 Mt CO 2 e in 2030. Realizing the threat of global warming, reducing Emissions from Deforestation and Degradation (REDD+) both the Kyoto Protocol in 1992 and Paris climate change agreement in 2012 were built. To upon these commitments Ethiopia has adopted a new, sustainable development model by initiating the Climate-Resilient Green Economy (CRGE) for achieving the following four pillars: i) Improving crop and livestock production while reducing emissions; ii) Protecting and reestablishing forests; iii) Expanding electricity generation from renewable sources v) Use of modern and energy-efficient technologies. Among many climate smart Agriculture practice in Ethiopia, Agroforestry is the one which is inclusive others agricultural practicing. The aims of this paper were to reviews the possible opportunities to raise the potential environmental role of agroforestry in supporting the climate smart agriculture in Ethiopia.Studies on indigenous agroforestry systems in southeastern Ethiopia indicated that, the average total biomass carbon stock were, Coffee accounted for 11 % and Enset 9% of total biomass C on average of which trees accounting for 39–93 % of the total biomass carbon stock. On the other hands, SOC stocks (0–60cm) were 109–253 Mg ha −1 in the indigenous agroforestry systems. Various agroforestry systems practice in different parts of Ethiopia has also contributed to biodiversity conservation. One of the oldest indigenous agroforestry systems that were practiced in Hararghe highlands of eastern Ethiopia is the retaining of scattered apple-ring Acacia ( Faidherbia albida (Delile).Therefore, an Agroforestry practice provides both provisioning and regulating services and there by contributing to the mitigation of global climate changes. Keywords , Agroforestry, climate change, climate smart DOI : 10.7176/JBAH/9-8-02 Publication date : April 30 th 2019

Use of sodium carbonate and sodium polyacrylate for the prevention of vinegar syndrome

ABSTRACTTo preserve archive films of which the base material is composed of cellulose acetate, we carried out screening tests on various reagents. We selected sodium carbonate and sodium polyacrylate as an acetic acid gas removing agent and a dehumidification agent, respectively. The performance of sodium carbonate per unit mass in the removal of acetic acid gas was superior to those of commercial products. The presence of sodium carbonate suppressed the increase in concentration of acetic acid gas for several months in film preservation containers. The neutralization of sodium carbonate with acetic acid gas was evaluated quantitatively. Sodium polyacrylate controlled relative humidity at around 40%RH in film preservation containers, and it was effective for film preservation. The dehumidifying performance of sodium polyacrylate compared favourably with those of commercial products. Thus, the materials tested in this study are found to be useful to avoid vinegar syndrome in cellulose acetate-based films.

Acoustic emission monitoring technology for coal and gas outburst

AbstractIn recent years, with the increase in mining depth and strength, coal‐rock gas dynamic disasters, such as coal and gas outburst, have shown an increasing trend. Acoustic emission (AE) technology has been viewed as a promising method that can effectively forecast coal and gas dynamic disasters. This paper first tests the AE characteristics of coal and rock samples during loading. Then, self‐developed AE continuous monitoring and early warning equipment is used to monitor and predict the coal and gas outburst dynamic disasters on the working face. And it is found that the coal samples primarily show ductile failure, and the AE exhibits the evolutionary characteristics of “rise‐peak‐fall”. The rock samples primarily exhibit brittle failure, and the AE evolution mode is almost no falling stage. Coal and gas outbursts occur after the stress peak. Before coal and gas outbursts occur, there is a clear increasing trend in the AE ahead of the gas concentration variation. When the gas‐bearing coal is damaged by the load, the coal body first breaks due to the stress, and the AE value increases. Then, due to the fracture of the coal body, the crack penetrates, gas rushes out, and the gas concentration increases. The research results can provide an advanced technical method for the monitoring and early warning of coal–rock gas dynamic disasters, and improve the prediction accuracy for dynamic disasters.

Gas sensing characteristics of the FET-type gas sensor having inkjet-printed WS2 sensing layer

This paper investigates the gas sensing characteristics of the MOSFET-type sensor having an inkjet-printed WS2 sensing layer. The drain current of the gas sensor increases when NO2 gas is injected into the test chamber since NO2 gas is an oxidizing gas that extracts electrons from the sensing layer. On the contrary, the drain current decreases when H2S gas is injected into the test chamber since H2S gas is a reducing gas that donates electrons to the sensing layer. In both cases, the change of the drain current increases as the gas concentration increases. However, for other gases (NH3 and CO2), the gas sensor has a small change of the drain current. The responses of the gas sensor to 10 ppm NO2, H2S, NH3, and CO2 gases are 15.20%, 7.18%, 1.66%, and 3.02%, respectively. Therefore, the WS2 sensor has a high selectivity for NO2 gas among the four target gases.

Pilihan Mitigasi Perubahan Iklim di Sektor Perhutanan Malaysia

The Intergovernmental Panel on Climate Change (2013) reported that more than half of the observed increase in global average surface temperature was caused by the anthropogenic increase in Greenhouse gas (GHG) concentrations and other anthropogenic forcings together. Continued emissions of GHGs will cause further warming and changes in all components of the climate system. Thus, limiting climate change will require substantial and sustained reductions of GHG emissions. Deforestation and burning of fossil fuels are the major anthropogenic source of carbon emission in the developing countries including Malaysia. Climate change mitigation options in the forestry sector could play an important role in reducing emissions and improving carbon sequestration. Therefore, this article attempts to identify the potential climate change mitigation options and their characteristics in the forestry sector of Malaysia. The major mitigation options include forest protection and conservation, afforestation, reforestation, sustainable forest management, enhanced natural regeneration, urban forestry, agroforestry, short rotation tropical tree plantations, and use of wood based bio-energy. This article suggests for a comprehensive research on the economic analysis of mitigation options which would be useful to address Malaysia’s emission reduction target in a cost-effective way.

A simple route for the preparation of nanostructured GdCoO3 via the solution method, as well as its characterization and its response to certain gases

Abstract This work presents the synthesis of perovskite GdCoO3 by a microwave-assisted solution method in order to test its possible application as a gas sensor. The crystal evolution, structure, composition, texture, morphology, and particle size were analyzed by X-ray diffraction, scanning and transmission electron microscopies, and nitrogen physisorption. Our synthesis route allowed to obtain GdCoO3 at lower temperatures and shorter reaction times than conventional methods. Measurements confirmed the formation of porous GdCoO3 microbases with a thickness of 7–13 μm. The GdCoO3 microbases were constituted by nanoparticles of size 10–20 nm. Additionally, crystallites of size 85–130 nm were observed distributed on the surface of the microbases, covering a surface area of around 19 m2/g. Pellets elaborated from GdCoO3 powders were tested as sensors in carbon monoxide and propane gaseous atmospheres at different temperatures and gas concentrations. The GdCoO3 showed a good performance as a gas sensor compared to other similar oxides. The oxide was clearly sensitive to the studied gases even at concentrations as low as 5 ppm at a temperature of 100 °C. The response of the material was homogeneous and increased with both the increase in temperature and gas concentration.

Detecting and explaining why aquifers occasionally become degraded near hydraulically fractured shale gas wells

Extensive development of shale gas has generated some concerns about environmental impacts such as the migration of natural gas into water resources. We studied high gas concentrations in waters at a site near Marcellus Shale gas wells to determine the geological explanations and geochemical implications. The local geology may explain why methane has discharged for 7 years into groundwater, a stream, and the atmosphere. Gas may migrate easily near the gas wells in this location where the Marcellus Shale dips significantly, is shallow (∼1 km), and is more fractured. Methane and ethane concentrations in local water wells increased after gas development compared with predrilling concentrations reported in the region. Noble gas and isotopic evidence are consistent with the upward migration of gas from the Marcellus Formation in a free-gas phase. This upflow results in microbially mediated oxidation near the surface. Iron concentrations also increased following the increase of natural gas concentrations in domestic water wells. After several months, both iron and SO42- concentrations dropped. These observations are attributed to iron and SO42- reduction associated with newly elevated concentrations of methane. These temporal trends, as well as data from other areas with reported leaks, document a way to distinguish newly migrated methane from preexisting sources of gas. This study thus documents both geologically risky areas and geochemical signatures of iron and SO42- that could distinguish newly leaked methane from older methane sources in aquifers.