CH4 Concentrations Research Articles

Climatic Impact on the Air Pollutant Concentrations Emitted from Gas Stations in Fallujah, Al-Anbar, Western Iraq

The research investigates the influence of climatic elements like temperature, relative humidity, rainfall, evaporation, dust storms, wind direction, and speed on the air pollutant concentrations at gas stations in Fallujah city while examining their impact on humans and the environment. This was achieved by measuring concentrations of CO, NO2, and CH4, suspended particles (TSP, PM10), and Cu, and Pb. It was found that the impact increased in July compared to January, because of the influence of the measured climatic elements. Rising temperatures increase air pollutants' concentrations in the atmosphere, while winds spread them from emission sites to distant locations. Moreover, summer temperatures significantly impacted air pollutant concentrations at the study stations, particularly at Al-Rehab gas station, with the highest recorded temperatures of 48.4°C. Some gas stations also exceeded local environmental limits for TSP, PM10, CO, NO2, and Pb. The study revealed that summer temperatures with wind speeds of 2.1 m/s resulted in the highest air pollutants values, while winter temperatures with wind speeds of 1.9 m/s decreased these values. Higher temperatures increase chemical reactions and temperature inversions, leading to increased pollution concentrations and exacerbating air quality problems in the study area. Strong winds disperse pollutants, reducing concentration in the study area, while low wind speed increases concentrations and stagnation, resulting in poor air quality in the studied sites. The importance of the current study lies in evaluating pollutants in the Fallujah city, determining their causes, the extent of the impact, and contribution of natural and human sources in causing changes in air pollutant concentrations; caused by emission from the source. Moreover, the current study showed its impact on human’s health, and trying to find solutions to limit these effects or reduce their levels to ensure the safety of the environment and health.

СO2-rich thermal waters of the Neitrino Research Gallery (Baksan Neitrino Observatory, North Caucasus)

Isotope-geochemical (δ2H and δ18O in H2O, δ15N in N2, δ13C in CO2 and CH4,3He/4He) studies of СО2-rich thermal waters (up to 41.3oC) which located in 4 km long tonnel of the Baksan Neutrino Observatory were carried out. The δ13C(CO2) values (–8.0… –6.4‰) indicate the volcanogenic genesis of CO2. The presence of the volcanogenic component is also emphasized by high values of 3He/4He (346 × 10–8). At the same time, nitrogen present in the gas phase is characterized by values of δ15N = +1.3‰, indicating its crustal genesis. In the tunnel, an elevated concentration of CH4 (up to 0.5%) was noted in one of the gas outlets. This methane is characterized by high δ13C values (–33.5 and –26.0‰), which, in general, are typical for other СО2-rich springs of the Eastern Elbrus Mountains. In contrast with the other CO2-rich springs of the North Caucasus, which are practically indistinguishable from surface waters in terms of δ2H and δ18O values, the CO2-rich thermal springs of the tunnel are noticeably enriched in heavy oxygen isotope (18O). This is a consequence of oxygen exchange between the waters and the host rocks at elevated temperatures. In the δ18O-δ2H diagram, the figurative points of thermal waters form a trend that reflects the mixing of isotope-light infiltration waters with isotope-heavy waters.

Sediment properties control riverine methane emissions: A case study of the Liao River in northern China

River and stream sediments act as biogeochemical reactors for greenhouse gases, particularly methane. However, understanding how riverbed sediment properties influence river carbon emissions remains relatively unclear. The Liao River in northern China is a typical watershed with heterogeneous water and sediment sources, characterized by varying sediment properties. In this study, we surveyed CH4 and CO2 emissions from its mainstem and tributaries during flood and dry seasons. We found consistent seasonal patterns in CH4 and CO2 emissions, with peaks occurring during the flood season. The average CH4 and CO2 fluxes were 1.64 ± 1.80 mmol·m−2·d−1 and 59.66 ± 44.60 mmol·m−2·d−1, respectively. Notably, the percentage of sediment silt was significantly correlated with CH4 concentration and flux (R2 = 0.12−0.30, p < 0.05). Fine particles dominated the availability of sediment organic matter and redox conditions, which were related to riverine CH4 production and emissions. Structural equation modeling revealed that both grain size and the percentage of TOC (total organic carbon) directly influenced riverine CH4 and CO2 emissions. The organic content and redox conditions of the riverbed sediment collectively explained 65% of riverine CH4 emissions, while grain size composition indirectly controlled CH4 emissions by altering sediment substrate quality and redox conditions. In contrast, river CO2 emissions were only weakly dependent on anaerobic metabolism in riverbed sediments. These findings enhance our understanding of the sources and metabolic mechanisms of riverine CH4 and CO2 emissions and offer potential improvements for estimating carbon fluxes in regional or global riverine networks by considering riverbed sediment properties.

Pollution gradients shape microbial communities associated with Ae. albopictus larval habitats in urban community gardens.

The Asian tiger mosquito Aedes albopictus is well adapted to urban environments and takes advantage of the artificial containers that proliferate in anthropized landscapes. Little is known about the physicochemical, pollutant, and microbiota compositions of Ae. albopictus-colonized aquatic habitats and whether these properties differ with noncolonized habitats. We specifically addressed this question in French community gardens by investigating whether pollution gradients (characterized either by water physicochemical properties combined with pollution variables or by the presence of organic molecules in water) influence water microbial composition and then the presence/absence of Ae. albopictus mosquitoes. Interestingly, we showed that the physicochemical and microbial compositions of noncolonized and colonized waters did not significantly differ, with the exception of N2O and CH4 concentrations, which were higher in noncolonized water samples. Moreover, the microbial composition of larval habitats covaried differentially along the pollution gradients according to colonization status. This study opens new avenues on the impact of pollution on mosquito habitats in urban areas and raises questions on the influence of biotic and abiotic interactions on adult life-history traits and their ability to transmit pathogens to humans.

Methane dynamics in the Baltic Sea: investigating concentration, flux, and isotopic composition patterns using the coupled physical–biogeochemical model BALTSEM-CH4 v1.0

Abstract. Methane (CH4) cycling in the Baltic Sea is studied through model simulations that incorporate the stable isotopes of CH4 (12C–CH4 and 13C–CH4) in a physical–biogeochemical model. A major uncertainty is that spatial and temporal variations in the sediment source are not well known. Furthermore, the coarse spatial resolution prevents the model from resolving shallow-water near-shore areas for which measurements indicate occurrences of considerably higher CH4 concentrations and emissions compared with the open Baltic Sea. A preliminary CH4 budget for the central Baltic Sea (the Baltic Proper) identifies benthic release as the dominant CH4 source, which is largely balanced by oxidation in the water column and to a smaller degree by outgassing. The contributions from river loads and lateral exchange with adjacent areas are of marginal importance. Simulated total CH4 emissions from the Baltic Proper correspond to an average ∼1.5 mmol CH4 m−2 yr−1, which can be compared to a fitted sediment source of ∼18 mmol CH4 m−2 yr−1. A large-scale approach is used in this study, but the parameterizations and parameters presented here could also be implemented in models of near-shore areas where CH4 concentrations and fluxes are typically substantially larger and more variable. Currently, it is not known how important local shallow-water CH4 hotspots are compared with the open water outgassing in the Baltic Sea.

Fiducial Reference Measurement for Greenhouse Gases (FRM4GHG)

The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks.

Technical feasibility and modeling of enzymatic pre-treatments of organic fraction of municipal solid waste to improve anaerobic digestion

The study explored the combined effects of enzymatic pre-treatment and anaerobic digestion (AD) on the organic fraction of municipal solid wastes (OFMSW) through experimental and multicriteria decision-making approaches. Five enzymes (UPP2, MPCS, USC4, USE2, and A. niger) and their dosages were studied. AD parameters included two inoculum origins (waste active sludge - WAS - and cow-agricultural sludge - CAS), the substrate: inoculum (SI) ratio, and inoculum incubation time (INOC). Desirability functions were used to optimize the multiple experimental responses simultaneously by converting each of them into values from 0 (unacceptable) to 1 (completely acceptable) and then combining these into a global desirability (D). D highlighted that higher enzyme dosages, INOC, and SI, improved AD performances, with optimal DOSE (at the highest level adopted for each enzyme) and INOC (5–10 d). AD tests with the five enzymes increased CH4 production by 10–13%v/v compared to untreated OFMSW. For UPP2 and MPCS, increasing DOSE boosted the biogas production, while increasing INOC enhanced the CH4 content. MPCS reached the highest efficiency (478. 43 NL CH4/kg VS with CAS, SI = 2:1, INOC = 10 d), followed by UPP2. Furthermore, higher INOC reduced A. niger doses, increasing CH4 production by 9%v/v compared to literature, with 5–10 d INOC (452.86 NL s/kg VS with WAS, SI = 2:1).

Medium-Term Monitoring of Greenhouse Gases above Rice-Wheat Rotation System Based on Mid-Infrared Laser Heterodyne Radiometer

The rice-wheat rotation system is a major agricultural practice in China as well as an important source of greenhouse gas (GHG) emissions. In this study, the developed mid-infrared laser heterodyne radiometer (MIR-LHR) was used for the remote sensing of atmospheric CH4 and N2O concentrations above the rice-wheat rotation system. From April 2019 to May 2022, the atmospheric column concentrations of CH4 and N2O above the rice-wheat rotation system were continuously observed in Hefei, China. The peak values of the N2O column concentration appeared 7~10 days after wheat seasonal fertilization, with additional peaks during the drainage period of rice cultivation. During the three-year rice-wheat crop rotation cycle, a consistent trend was observed in the CH4 column concentrations, which increased during the rice-growing season and subsequently decreased during the wheat-growing season. The data reveal different seasonal patterns and the impact of agricultural activities on their emissions. During the observation period, the fluctuations in the CH4 and N2O column concentrations associated with the rice-wheat rotation system were about 40 ppbv and 6 ppbv, respectively. The MIR-LHR developed for this study shows great potential for analyzing fluctuations in atmospheric column concentrations caused by GHG emissions in the rice-wheat rotation system.

Methylotuvimicrobium alcaliphilum 20Z based ectoine production from various industrial CH4 sources: Cultivation optimization and comprehensive analysis

Methanotroph-based CH4 conversion technology is being widely studied due to its advantages of mild operating conditions and environmental friendliness. In this study, operating strategies were investigated for industrial CH4 sources in order to widely disseminate methanotroph-based CH4 conversion technology using the promising strain, Methylotuvimicrobium alcaliphilum 20Z. The optimal O2/CH4 ratio for extremely different CH4 concentrations was explored based on kinetic-based simulation for biological reaction, and experimentally proven using fermenter-scale experiments. As a result, when high CH4 concentration is used, ectoine production rate can be maximized (33.8 mg/L·h) at an O2/CH4 ratio of 1 while favoring the “production of metabolites”. On the other hand, in the low CH4 concentration case, when changing from the general O2/CH4 ratio of 4 to the optimal O2/CH4 ratio (i.e., 1), although the improvement in ectoine concentration was not noticeable (3.9 to 7.5 mg/L·h), the CH4 conversion rate rapidly decreased (50 to 20 %), suggesting that the focus in the low concentration case should be on “removal of CH4”. In the case of biogas, the rapid pH drop caused by the large amount of CO2 in the feed is offset by a buffer solution, and the concentration of Na+ ions increases during the overall reaction time. Therefore, the production of metaboiltes can be maximized while simultaneously controlling pH and Na+ ion through continuous operation with a high dilution rate (19.8 mg/L·h). Furthermore, major performance indicators for each industrial gas were derived through comprehensive comparative analysis, through which the “dual-functions” of methanotrophs could be emphasized. This study provides a practical and strategic approach for methanotrophs that can flexibly respond to diverse industrial CH4 sources.

Bridging gas and aerosol properties between the northeastern US and Bermuda: analysis of eight transit flights

Abstract. The western North Atlantic Ocean is strongly influenced by continental outflow, making it an ideal region to study the atmospheric transition from a polluted coastline to the marine environment. Utilizing eight transit flights between the NASA Langley Research Center (LaRC) in Hampton, Virginia, and the remote island of Bermuda from NASA's Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE), we examine the evolution of trace gas and aerosol properties off the US East Coast. The first pair of flights flew along the wind trajectory of continental outflow, while the other flights captured a mix of marine and continental air mass sources. For measurements within the boundary layer (BL), there was an offshore decline in particle N&lt;100 nm, N&gt;100 nm, CH4, CO, and CO2 concentrations, all leveling off around ∼900 km offshore from the LaRC. These trends are strongest for the first pair of flights. In the BL, offshore declines in organic mass fraction and increases in sulfate mass fraction coincide with increasing hygroscopicity based on f(RH) measurements. Free troposphere measurements show a decline in N&lt;100 nm, but other measured parameters are more variable when compared to the prominent offshore gradients seen in the BL. Pollution layers exist in the free troposphere, such as smoke plumes, that can potentially entrain into the BL. This work provides detailed case studies with a broad set of high-resolution measurements to further our understanding of the transition between continental and marine environments.

Improving the anaerobic digestion of sewage sludge by adding cobalt nanoparticles

ABSTRACT This work evaluated the effects of cobalt nanoparticles (CoNPs) (0.025–7 mg/gVS) on the intensification of sewage sludge anaerobic digestion (AD) using biochemical methane potential (BMP) tests. This study was motivated by the need to improve the efficiency and stability of anaerobic digestion of sewage sludge, a critical process in waste management and renewable energy production. The effects at doses less than 2 mg/gVS were not substantial, but 3–7 mg/gVS improved the performance. The maximum biogas yield was 232 mL/gVS (at a dose of 7 mg/gVS), whereas it was 132 mL/gVS in the control (zero dose). Similarly, the reductions in the volatile solids and methane contents reached maxima of 16 and 74.3%, respectively. The analyses of volatile fatty acids, redox potential, and electron transfer system activity indicated that the addition of CoNPs stimulated the early stages of AD. Finally, acetate consumption and the increase in CH4 content suggested that CoNPs positively affected system stability and acetoclastic methanogenesis. That is, CoNPs effectively intensified the behaviour and stability of the anaerobic process. The novelty of this research lies in the comprehensive evaluation of the effects of CoNPs across a wide range of doses on sewage sludge AD, providing new insights into the optimisation of this process for increased biogas production and organic matter reduction.

Simultaneous measurement of temperature and C2H4 concentration in hydrocarbon flames using interference-immune differential absorption spectroscopy at 3.3 μm

In diagnostic applications based on tunable diode laser absorption spectroscopy, the measurement of target substances can be influenced by factors such as background thermal radiation in the combustion environment, extinction caused by solid or liquid particles, and other interfering absorptions. In this work, we developed a differential absorption diagnostic technique based on wavelength pairs, utilizing an interband cascade laser near 3.3 μm to simultaneously measure temperature and C2H4 concentration in hydrocarbon flames. Based on a detailed study of the C2H4 spectrum in this region and considering the optimal standard for spectral lines, two wavelength pairs were selected. The temperature is determined by the ratio of the absorption cross-sections of two wavelength pairs, and the C2H4 concentration is inferred based on the wavelength pair with higher differential absorption. In the initial stage, the system’s accuracy was verified in high-temperature static conditions (T = 300–800 K, P = 1 atm), and continuous time series measurements demonstrated the system’s stability. The limit of detection achieved by Allan-Werle variance analysis is 2.5 ppm at the optimal average time of 100 s. Subsequently, measurements were taken in a hydrocarbon flame. The obtained results indicate an average deviation of 1.021 % between the measured temperature in the flame and the reference value, with a standard deviation of 1.381 % for concentration measurement. All the measurements show that the system can be potentially applied to combustion diagnosis.

PSXII-29 Effect of tannins level and diet type on in vitro ruminal fermentation and methane production

Abstract The objective of the study was to evaluate the effect of four levels of a commercial product based on quebracho that contains tannins (Table 1) on three types of diets: Feedlot, Dairy Cattle, and Grazing, using the in vitro gas production technique on ruminal fermentation, dry matter digestibility and methane (CH4) production to determine its potential use as a greenhouse gas mitigation strategy in ruminants. An in vitro trial was carried out in a completely randomized block design with a factorial arrangement of 4 [dose: 0, 0.25, 0.50, and 0.75 % of Protein Enhancer (PE)] x 3 [diet types: low (LFD), medium (MFD) and high forage (HFD)]. The fermentation of each treatment was carried out in triplicate in 120 mL amber antibiotic bottles, containing 0.5 g of substrate previously deposited in nylon bags (24 µm pore size) and 60 mL of a mixture of medium and rumen fluid from three Holstein cows. Incubations were replicated in two independent runs (blocks). The gas pressure (PSI) was recorded at 1, 2, 3, 6, 9, 12, 18, 24, 30, 36, 48, 60 and 72 hours of incubation. Gas pressure data were converted to gas volume (y = mL of gas; x = gas pressure PSI). Subsequently, pH was measured, and subsamples for analysis of volatile fatty acids (VFA) by gas chromatography were collected. Methane was analyzed with a Crowcon Gas-Pro detector, while ammoniacal nitrogen with a hybrid multimodal microplate reader. The data were analyzed with the MIXED procedure of SAS, and the comparison of means was analyzed with Tukey and with orthogonal polynomials for doses. An interaction (P &amp;lt; 0.05) was observed between diets and PE levels for CH4 concentration (%), where the diet with a greater level of forage and the greatest level of PE (0.75%), showed the least concentration (30%, P &amp;lt; 0.05) compared with the control diet of dairy cattle. On average, CH4 production [mL CH4/g dry matter (DM)] were 83.3, 63.6, and 35.3 for LFD, MFD, and HFD, respectively (Table 2). As the dose of PE increased, rumen pH and N-NH3decreased (P &amp;lt; 0.05), and the total VFA concentration increased (linear effect, P &amp;lt; 0.05; Table 3). Methane production was less (30%) with the grass-based diet and the greatest level of quebracho-based product with condensed tannins, compared with the dairy cattle diet with 0% condensed tannins. The diet for feedlot cattle was more digestible and, therefore, produced more gas and a greater concentration of CH4, in contrast to the grass-based diet, which produces less CH4. It is necessary to carry out in vivo trials, particularly in grazing cattle, to evaluate the effect of the quebracho-based product on performance and in vivo methane emission. This study was partially funded by PAPIIT-DGAPA-UNAM (grant IN212523).

Very high cycle fatigue properties of ultrahigh strength steels in the presence of hydrogen

The very high cycle fatigue (VHCF) properties of 2000 MPa ultrahigh strength martensitic steels after hydrogen pre-charging were investigated by means of ultrasonic fatigue tests. Results showed that the VHCF lives of the experimental steels were drastically decreased by about two orders after pre-charged with a hydrogen concentration of CH = 1.23 wppm. The experimental steel tempered at a higher temperature of 300 °C with some epsilon-carbides and a lower density of dislocations showed higher VHCF lives in the presence of hydrogen. It could be attributed to the lower hydrogen diffusion coefficient since hydrogen might accelerate fatigue crack propagation in the granular bright facet (GBF) area.

Robust prediction for characteristics of digestion products in an industrial-scale biogas project via typical non-time series and time-series machine learning algorithms

Anaerobic digestion (AD) is a well-established pathway for treating agricultural organic waste, and machine learning has emerged as a novel tool to predict its product performance. In prior research, the majority of studies concentrated on non-time series models for laboratory-scale fermentation data. Consequently, the generalization performance of these models was significantly constrained, particularly in the context of industrial-scale biogas projects. Thus, in this study, typical non-time series models (GBR and RF) and time-series models (LSTM, CNN-LSTM, and DA-LSTM) after hyperparameter optimization were chosen to accurately predict the characteristics of digestion products in a biogas project. The ideal GBR model for CH4 content was obtained, and the R2 values of the test set and training set were 0.93 (RMSE=1.11) and 0.97 (RMSE=0.69), respectively. Temperature was the most important parameter for biogas production according to feature importance and SHAP analysis of the RF model. The DA-LSTM was superior to LSTM and CNN-LSTM for the prediction of biogas production, and the R2 of DA-LSTM was 0.87 (RMSE=1048.14) with a seq_len of 10 d. This study provides direction for high-efficiency biogas production in wet biogas projects with the aid of reliable machine learning models.

The Used of Variuos Biomass Waste as Raw Material Biogass Production using Cow Dung as Source of Microbe by Continuously-Anaerobic Fermentation on the 15 Liter Reactor

In Indonesia, there were some biomass wastes if there not treatment, will cause quality- environmental decreasing. It is need effort to minimalize negative effect of those biomass wastes by treating to higher value product. The organic materials in the biomass waste could be anaerobically fermentatation degradated to produce biogass. The anaerobic fermentation were depended on the use of raw materials and microorganism. The organic wastes that use as raw material on this research were (1) tapioca industrial wastewater,(2) tofu industrial wastewater, (3) fruits-peel wastes and (4) vegatable wastes. The source of microbe were found from cow dung The reaserch purpose were to know the influence of the kind of raw materials on the biogas production using cow dung as source of microbe. The research were done at Engineering Faculty Laboratry, Malahayati University Bandarlampung on the 15 liter continuously-anaerobic bioreactor with 15 days retention time. The influen were added 2 liter/2days continuously. The tested variable were COD and biogas composition. The research result showed that the COD in the tapioca industrial wastewater were reduced 71.00 – 89.5 %, in the tofu industrial wastewater reduced 70.00 – 75.00 %, in the fruit-peel waste reduced 7.00-86.00 % andin the vegetable waste reduced 65.00 – 67 %. The CH4 concentration in the produced biogas were 57.63 % ; 40,75 %; 41,41 % and 40.64 %. The C/N ratio effluent between 7.94 – 14.08 could be used directly as liquid organic fertilizer The research conclusion were the production biogas using tapioca industrial wastewater showed the best result . That cause tapioca industrial wasterawte contain high carbohydrate concentration. In the anaerobic digestion, the carbohydrate material were degradated to CH4 (methane)

Part-per-Billion (Ppb)-Level Acetylene Sensor Employing Optical Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) with an Erbium-Doped Fiber Amplifier (EDFA) and a Fiber-Optic Fabry–Perot Interferometer

An all-optical double-pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for the detection of acetylene (C2H2) at part-per-billion (ppb) levels was developed and experimentally validated. By employing an erbium-doped fiber amplifier (EDFA) capable of emitting up to 1 W of optical power, a commercial quartz tuning fork (QTF) resonating at 30.7 kHz, and double-pass acoustic microresonators, the amplitude of the QEPAS signal was significantly enhanced, thereby improving the sensitivity of the C2H2-QEPAS sensor. Instead of using piezoelectric detection in conventional QEPAS, a highly sensitive fiber-optic Fabry–Perot interferometer (FPI) was employed to measure the vibration of the QTF prong. A working point self-stabilizing technique was exploited to improve the demodulation sensitivity and stability. The linear response of the sensor to laser power and C2H2 concentration confirmed that no saturation occurred. With an excitation laser power of 1 W and a C2H2 absorption line of 1532.83 nm, a C2H2 minimum detection limit (MDL) of 19.1 ppb was achieved, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.58 × 10−8 cm−1∙W∙Hz−1/2. Owing to its high sensitivity, long-term stability, and immunity to electromagnetic interferences, the QEPAS sensor provides considerable potential for remote gas sensing in environmental monitoring and other applications.

Advanced soil-gas geochemical exploration methods for orogenic gold deposits: A case study of Chalapu deposit, Xizang

Orogenic gold deposits play a significant role in the world’s gold reserves, and their distinctive characteristics pose challenges for exploration. The low sulfide content and narrow, fault-controlled sulfide-quartz veins hinder the use of traditional mineral exploration methods to locate deeply buried ore bodies, particularly in regolith-covered areas. Enhanced methods are required to detect deposits at greater depths. Soil gas composition shows promising potential for mineral exploration by conveying information about sulfur-rich and carbon-rich gases related to deep-seated mineralization into surface soils. However, the prospects of this method for gold deposits remain uncertain. In this study, a novel method was introduced to perform an integrated H2S, SO2, CH4, and CO2 soil-gas geochemical survey on gold ore bodies of different scales at the Chalapu deposit in Tibet. The results unveiled notable gas geochemical anomalies of H2S, SO2, CH4, and CO2 above the multi-layered or thick gold ore bodies. For instance, on exploration line 16 at point A1607, H2S reached the regional maximum value of 1.064 ppm, coinciding with the surface exposure of the thickest gold ore body, measuring 19.81 m. While the presence of CH4 and CO2 anomalies alone may not signify potential mineralized zones, the combined presence of anomalous H2S and SO2 values along with CH4 and CO2 concentrations appears to be effective in identifying mineralization. These combinations of geochemical anomalies not only uncover concealed ore bodies, but also delineate the trend and extension direction in strike and dip of ore bodies. Gas intensity may provide insights into the scale of the ore bodies, with stronger gas anomalies observed in areas with thicker ore bodies at similar depths. Thus, the study reveals that soil-gas exploration shows great promise as an exploration technique for orogenic gold deposits, especially in areas with regolith cover hindering traditional methods from detecting mineralized zones for gold exploration.

Spatio-Temporal Assessment of Air Quality in Rajsamand District, Rajasthan Using Cloud-Based Google Earth Engine Approach

This study examines the spatial and temporal variations of key air pollutants in Rajsamand District, Rajasthan, from January 2015 to December 2019, using Sentinel-5P TROPOMI data. The pollutants analysed include carbon monoxide (CO), nitrogen dioxide (NO2), formaldehyde (HCHO), sulphur dioxide (SO2), methane (CH4), and aerosols. The findings reveal significant impacts of marble mining activities on local air quality. CO levels increased notably near mining sites, with mean annual values rising from 0.022 mol/m2 in 2015 to 0.026 mol/m2 in 2019. NO2 concentrations peaked near urban and industrial areas, increasing from 0.00013 μg/m3 in 2015 to 0.00016 μg/m3 in 2019. Elevated HCHO levels were observed near mining clusters, with concentrations rising from 0.00018 μg/m3 in 2015 to 0.00021 μg/m3 in 2019, posing significant respiratory health risks. SO2 emissions, primarily from diesel machinery and blasting activities, increased from 0.00028 ppm in 2015 to 0.00031 ppm in 2019. CH4 concentrations, influenced by underground releases during mining, increased from 1795 ppm in 2015 to 1810 ppm in 2019. Aerosol levels, elevated due to dust emissions from mining, increased from 0.48 μg/m3 in 2015 to 0.51 μg/m3 in 2019. These results underscore the need for stringent air quality regulations and sustainable mining practices to mitigate environmental and health impacts in Rajsamand District.

Riparian vegetation influences aquatic greenhouse gas production in an agricultural landscape

Although riparian vegetation is widely acknowledged for its positive impact on soil and water quality and its role in regulating terrestrial greenhouse gas emissions in agricultural landscapes, there remains a gap in understanding how different types of riparian vegetation affect aquatic greenhouse gas production. Thus, the objective of this study was to investigate whether the type of vegetation within riparian zones influenced aquatic environmental factors, subsequently impacting aquatic greenhouse gas emissions. To address this, we measured greenhouse gases in the aquatic environment bordered by riparian zones with herbaceous vegetation (GRS) compared to undisturbed natural riparian forests dominated by deciduous (UNF-D) or coniferous (UNF-C) vegetation or a rehabilitated riparian forest (RH). Our findings indicate that aquatic CO2 concentrations were not influenced (p < 0.05) by vegetation type ranging from 9 g L−1 to 11 g L−1. In contrast, aquatic CH4 concentrations were significantly lower (p < 0.05) in treed riparian zones, ranging from 14 μg L−1 to 24 μg L−1, compared to a riparian zone with herbaceous vegetation (34 μg L−1). However, we observed significantly higher (p < 0.05) aquatic N2O concentrations in treed riparian zones (9.5 μg L−1 to 10.3 μg L−1), particularly those dominated by coniferous vegetation (23.0 μg L−1), compared to the riparian zone with herbaceous vegetation (7.7 μg L−1). The total CO2-C equivalent (i.e., CO2 + CH4 + N2O) was highest in the riparian zone with coniferous trees (UNF-C: 10,717 mg CO2-Ceq L−1), followed by the GRS (9494 mg CO2-Ceq L−1), RH (9423 mg CO2-Ceq L−1) and UNF-D (9,183 mg CO2-Ceq L−1) riparian zone. Moreover, riparian vegetation was influenced by various environmental factors that likely controlled physicochemical and biological processes related to the production of greenhouse gases within the aquatic environment.