Ambient Gas Concentrations Research Articles

Rainwater Quality Disparities Across Malaysian Peninsula Sites

This research describes the physicochemical quality of harvested rainwater at four distinct locations in Peninsula Malaysia. The evaluation of rainwater quality across different geographic areas aims to provide valuable insights into potential variations and trends in rainwater quality to reduce water demand globally. This analysis is conducted to determine seven properties, namely ammoniacal nitrogen, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), dissolved oxygen (DO), pH, total dissolved solids (TDS), and turbidity. The results demonstrate that the quality of harvested rainwater meets the raw water quality standards set by the World Health Organization (WHO) and the National Water Quality Standards for Malaysia (NWQSM), indicating good quality rainwater in Malaysia. However, the COD for rainwater in all locations exceeded the limit, with a range of 14.1 to 29.7 mg/L, while the maximum limit for COD set by WHO is 10 mg/L, and according to NWQSM standards, it is 10–100 mg/L. The average pH of the collected rainwater is acidic ranged from 4.7 to 5.56. BOD5 for the collected rainwater is excellent; however, L2 has a slightly higher BOD5 at 6.5 mg/L, whereas the recommended limit by WHO is 6 mg/L, and the NWQSM standard suggests a range of 1–12 mg/L, with a standard limit of 5–7 mg/L. Nevertheless, DO levels ranged from 7.71 to 7.76 mg/L, indicating an ambient gas concentration in the rainwater. The collected rainwater can be used for portable purposes, gardening, smart farming, and toilet flushing.

Application of flame-formed carbon nanoparticle films for ethanol sensing

Carbon nanoparticles (CNPs) have received considerable attention due to their exceptional qualities and adaptability. Their unique physical and chemical characteristics make them extremely intriguing as materials for numerous high-potential applications, such as electronics and gas sensing. This study focused on producing carbon-based nanomaterial devices by deposition of flame-formed carbon nanoparticles on a suitable substrate and investigating their gas-sensing properties. CNPs were produced in a fuel-rich laminar premixed ethylene/air flame and the collected CNP film was morphologically and electrically characterized. The electrical conductivity of the film was investigated as a function of ethanol concentration and amount of deposited material. Notably, CNP films exhibited high sensitivity to ambient ethanol gas concentrations, and rapid recovery times at room temperature, and showed a sensitivity increasing with the amount of deposited material and the surface complexity. Our findings demonstrate the high potential of combustion-generated CNPs as building materials for low-cost and portable ethanol sensors.

Study on Combustion Characteristics of Low Concentration Coalbed Methane Induced by Hydrogen Jet based on Excess Air Ratio

Low concentration coal bed gas used for power generation is a better treatment scheme at present, which solves the problem of environmental pollution caused by the direct emptying of coal bed gas. Coal bed methane is a methyl alkyl fuel, and slow combustion rate will cause abnormal combustion phenomena such as large combustion cycle changes. The initial ambient gas concentration has a great influence on the development and propagation of the flame. In this paper, a constant volume bomb model is established to change the excess air coefficient of methane air premix in the initial constant volume bomb, and the change law of combustion heat release is analyzed. The results show that when hydrogen participates in the combustion stage, the combustion rate increases with the increase of excess air coefficient. When hydrogen is burned out, the combustion rate decreases with the increase of excess air coefficient.

Suppress ambient temperature interference strategy based on SnO2 gas semiconductor sensor using dynamic temperature modulation mode and principal component analysis algorithm

Semiconductor gas sensors have been widely used in environmental monitoring, toxic gas monitoring, respiratory marker monitoring and other fields due to their low price and high sensitivity etc. An easily overlooked parameter, ambient temperature, is a major factor affecting the accuracy of the sensor. In this paper, a new idea to suppress ambient temperature interference is proposed. Dynamic temperature modulation method is used to extend the dimension of output information, so that both ambient temperature and target gas concentration can be expressed simultaneously. The ambient temperature component is separated by coordinate transformation and component elimination. The data inverse transformation is carried out to achieve the purpose of suppressing the ambient temperature interference. Compared with the performance optimization of gas-sensing materials and additional temperature sensors, the first advantage of this method is to reduce the complexity and power consumption of sensor devices. In addition, the use of PCA algorithm also reduces the complexity of the recognition algorithm. At the same time, more intuitive data reduces the cost of parameter optimization.

Errors in ambient gas concentration measurement caused by acoustic response of electrochemical gas sensors

Electrochemical sensors are used to measure electroactive gases in ambient air monitoring applications. These sensors typically contain sulfuric acid electrolyte, and porous carbon working, reference, and counter electrodes. Current fluctuations caused by fluctuations in the meniscus contact shape or area at the 3 phase gas-electrolyte-electrode interface as a result of ambient pressure fluctuations have been suggested as a potentially significant source of error in sensor measurements. We confirm in the present work that the pressure oscillations associated with ambient sound can indeed lead to significant signals. We show, for a variety of commercial sensors for ambient nitrogen dioxide (NO2), that acoustic noise equivalent to that from a nearby motorcycle or heavy goods vehicle can cause transient current fluctuations at 2 Hz sampling rate equivalent in the sensor output to as much as that due to 100 parts per billion by volume (ppb) of NO2, and with a root mean square (RMS) variation averaged over 10 s of approximately 40 ppb equivalent. These observations indicate that electrochemical gas sensors can behave as “microphones” in response to loud noise. The impact of acoustic noise should be considered when using electrochemical sensors to measure ambient air quality in areas of significant noise pollution, particularly if the aim is to resolve local transient concentration variations.

Effects of High-Concentration CO2 on Ignition Delay Time of 70% n-Heptane/30% Toluene Mixtures

In order to research the high-concentration CO2 effects on ignition delay time (IDT) of diesel surrogate fuel (70% n-heptane/30% toluene), a carbon dioxide effect (CDE) model is established, which considers fuel and ambient gas concentration, density, and temperature influence on autoignition under CO2/O2 atmosphere. Firstly, a chemical model of n-heptane/toluene is established, and the coupling, reduction, and simulation processes are carried out in chemical kinetic software with the IDT as the target parameter. Secondly, a constant volume combustion chamber (CVCC) visualization platform is built by incorporating a high-speed camera system and different working conditions are set in the CO2 volume fraction range (40%-70%) at 3.0 MPa and 850 K for an autoignition experiment. Thirdly, experiment and simulation results are discussed in air, 60% CO2/40% O2, 50% CO2/50% O2, and 40% CO2/60% O2 atmospheres, including the IDT, CO2 effects, temperature sensitivity, and OH radical rate of production (ROP). The results show that the CDE model well predicts the 70% n-heptane/30% toluene IDT under the CO2/O2 atmosphere and the average error in 60% CO2/40% O2 atmosphere is 5.29%. Besides, when the CO2 volume fraction increases from 40% to 60%, the CO2 thermal effect plays a leading role in the IDT prolongation and the OH radical ROP peak of R4 (O+H2O⟶2OH) decreases by 180%.

Errors in Ambient Gas Concentration Measurement Caused by Acoustic Response of Electrochemical Gas Sensors

Errors in Ambient Gas Concentration Measurement Caused by Acoustic Response of Electrochemical Gas Sensors

Atmospheric concentrations and ecosystem fluxes of CH2Cl2, CHCl3 and CCl4 along tidal and vegetation gradients within a coastal salt marsh in Eastern China

There is a causal relationship between atmospheric concentrations and ecosystem fluxes of DCM, CF, and CT. Atmospheric concentrations of these gases likely regulate ecosystem fluxes, and they may also be influenced in turn by exchanges with the ecosystem. The relationship between atmospheric concentrations and fluxes of DCM, CF, and CT is bound to affect the occurrence and fate of these gases in the environment. However, how atmospheric concentrations and ecosystem fluxes are related remains poorly understood. Here, the dynamics of atmospheric concentrations and ecosystem fluxes of these three gases were investigated using samples from three transects along tidal and vegetation gradients within a coastal salt marsh in Eastern China. Substantial variation was found among the dynamics of the three gases, which also showed different relationships between their atmospheric concentrations and ecosystem fluxes. In general, the ecosystem flux of each gas was negatively correlated with its ambient concentration in the atmosphere, although this varied across time and space. For example, high ambient concentrations of DCM and CT often corresponded with high ecosystem fluxes, but high ambient concentrations of CF corresponded to low ecosystem fluxes. Gas fluxes were significantly correlated, suggesting that the three gases have a common source. However, there may be differences between marine and terrestrial inputs, helping to explain the inconsistent flux-atmospheric concentration relationships. External inputs (e.g., coastal seawater and terrestrial biomass burning) may act to regulate ambient gas concentrations in the coastal salt marsh atmosphere, altering patterns of exchange between the ecosystem and atmosphere. Salt marsh ecosystems may be worthy of attention as sinks for DCM, CF, and CT. Ecological restoration of coastal salt marshes is therefore critical to help mitigate high atmospheric concentrations of DCM, CF, and CT.

Inhibitor-coated enhanced-efficiency N fertilizers for mitigating NOx and N2O emissions in a high-temperature irrigated agroecosystem

Nitrogen (N) fertilizers have substantially increased global crop yields around the world during recent decades. Nevertheless, the extensive use of N fertilizers at global scale has converted agricultural fertilized soils into an important anthropogenic source of nitrous oxide (N2O) and nitric oxides (NO+NO2 = NOx). The application of enhanced-efficiency N fertilizers, with the addition of urease and nitrification inhibitors (UI and NI, respectively), facilitates the reduction of N2O and NOx emissions and the improvement of agronomic responses.Despite the fact that soil N2O emissions have been widely studied under a large variety of climatic conditions and with different enhanced-efficiency N fertilizer, few studies have focused on soil NOx emissions, particularly in high temperature environments. The main aim of this study, therefore, was the quantification of NO and NO2 fluxes at a high temporal resolution using an automatic measurement system with the capacity to evaluate 5 different treatments with three replicates, and the ambient gas concentration. In addition, N2O emissions were measured with the static chamber method. With respect to the urea (U) treatment, the results confirm a significant mitigation of N2O and NO losses with the use of the new experimental inhibitor, DMPSA, alone or combined with the urease inhibitor NBPT. Overall, NOx emissions decreased by more than 60% in all the treatments in which synthetic inhibitors (both UI and NI) were applied, while N2O emissions were reduced by more than 35% in all the fertilized treatments when compared with urea alone.The high temporal resolution allowed the observation of negative fluxes of NO and NO2 in the different treatments, although these were more frequent and intense in the U+NI treatment. In general, grain and biomass yield were not affected by the use of NI or UI. The combined result was that a substantial reduction of yield-scaled-N2O and yield-scaled-NOx emissions was obtained when these inhibitors were used with urea and, therefore, their use should be recommended for mitigating these emissions whilst maintaining yields.

Analysis of evaporation characteristics and heat transfer for flash-boiling sprays

In order to improve engine thermal efficiency with reduced emissions, substantial studies have been carried out to improve the atomization and evaporation of fuel sprays, as well as fuel-air mixing in the engine cylinder. It has been found that flash-boiling spray is an effective way to achieve these goals. To further understand the evaporation characteristics and hear transfer phenomena between flash-boiling sprays and ambient gas, liquid temperature and vapor concentration of flash-boiling spray were measured quantitatively using laser induced exciplex fluorescence (LIEF) technique. The effects of fuel temperature, ambient pressure and superheated index (Pa/Ps) on the evaporation characteristics and heat transfer of fuel spray were investigated. The experimental results demonstrate that compared with non-flash-boiling spray, the rapid evaporation of flash-boiling spray leads to a higher vapor concentration along the center line. Meanwhile, the remarkable amount of energy absorbed from liquid phase of flash-boiling spray results in a faster liquid temperature decrease along the center line. When hot fuel is injected into cold environment, increasing fuel temperature leads to an increase of heat transfer from fuel spray to ambient gas because of the higher temperature difference between them. On the other hand, increasing ambient pressure decreases the evaporation rate of fuel spray due to the higher Pa/Ps. As such, the energy absorbed for fuel evaporation from liquid phase of spray is decreased, the heat transfer from fuel spray to ambient gas is increased.

Ammonia and greenhouse gas emissions at beef cattle feedlots in Alberta Canada

This study was conducted at beef cattle feedlots, over two years in southern Alberta Canada, and focused on deriving the ammonia, methane, nitrous oxide and carbon dioxide emissions from two feedlots from June/July to October. Line-averaging sensors were used to measure ambient gas concentrations in the vicinity of the feedlots, and an inverse dispersion method was used to calculate emissions. Results show that ammonia and methane emissions were consistent with that measured from other studies. Both feedlots lost about 40% of the nitrogen feed intake as ammonia. The emission of nitrous oxide, when compared on a greenhouse gas bases, was similar to the methane emission. A diet difference between feedlots coincided with a slight difference in feedlot methane emission. There was good agreement between previously reported ammonia and methane emission rates and those derived in our feedlot study. Further evaluation of the underlying relationships causing variation in emissions should follow. A key to understanding emissions at commercial feedlots is to fully engage the management data available.

Use of electrochemical sensors for measurement of air pollution: correcting interference response and validating measurements

Abstract. The environments in which we live, work, and play are subject to enormous variability in air pollutant concentrations. To adequately characterize air quality (AQ), measurements must be fast (real time), scalable, and reliable (with known accuracy, precision, and stability over time). Lower-cost air-quality-sensor technologies offer new opportunities for fast and distributed measurements, but a persistent characterization gap remains when it comes to evaluating sensor performance under realistic environmental sampling conditions. This limits our ability to inform the public about pollution sources and inspire policy makers to address environmental justice issues related to air quality. In this paper, initial results obtained with a recently developed lower-cost air-quality-sensor system are reported. In this project, data were acquired with the ARISense integrated sensor package over a 4.5-month time interval during which the sensor system was co-located with a state-operated (Massachusetts, USA) air quality monitoring station equipped with reference instrumentation measuring the same pollutant species. This paper focuses on validating electrochemical (EC) sensor measurements of CO, NO, NO2, and O3 at an urban neighborhood site with pollutant concentration ranges (parts per billion by volume, ppb; 5 min averages, ±1σ): [CO] = 231 ± 116 ppb (spanning 84–1706 ppb), [NO] = 6.1 ± 11.5 ppb (spanning 0–209 ppb), [NO2] = 11.7 ± 8.3 ppb (spanning 0–71 ppb), and [O3] = 23.2 ± 12.5 ppb (spanning 0–99 ppb). Through the use of high-dimensional model representation (HDMR), we show that interference effects derived from the variable ambient gas concentration mix and changing environmental conditions over three seasons (sensor flow-cell temperature = 23.4 ± 8.5 °C, spanning 4.1 to 45.2 °C; and relative humidity = 50.1 ± 15.3 %, spanning 9.8–79.9 %) can be effectively modeled for the Alphasense CO-B4, NO-B4, NO2-B43F, and Ox-B421 sensors, yielding (5 min average) root mean square errors (RMSE) of 39.2, 4.52, 4.56, and 9.71 ppb, respectively. Our results substantiate the potential for distributed air pollution measurements that could be enabled with these sensors.

Acetone gas sensors composed of carbon nanotubes with adsorbed Au nanoparticles on plastic substrate

Carbon nanotubes (CNTs) have been demonstrated to be one of the most interesting materials for gas sensing. This study applies a simple method for the direct transfer of high-density CNTs from a SiO2/Si substrate to a flexible substrate for acetone gas sensing at room temperature. The flexible gas sensor exhibited high sensitivities of 4.63% at room temperature for ambient acetone gas concentrations of 800 ppm, respectively. In addition, the gas response of the CNT-based chemiresistor is attributed to p-type conductivity in the Au-modified semiconducting CNTs. Very good repeatability of the sensor response to gas concentration is demonstrated, representing a major step toward the low-cost large-scale production of this class of device.

Identification and distribution of neuronal nitric oxide synthase and neurochemical markers in the neuroepithelial cells of the gill and the skin in the giant mudskipper, Periophthalmodon schlosseri

Mudskippers are amphibious fishes living in mudflats and mangroves. These fishes hold air in their large buccopharyngeal-opercular cavities where respiratory gas exchange takes place via the gills and higher vascularized epithelium lining the cavities and also the skin epidermis. Although aerial ventilation response to changes in ambient gas concentration has been studied in mudskippers, the localization and distribution of respiratory chemoreceptors, their neurochemical coding and function as well as physiological evidence for the gill or skin as site for O2 and CO2 sensing are currently not known. In the present study we assessed the distribution of serotonin, acetylcholine, catecholamines and nitric oxide in the neuroepithelial cells (NECs) of the mudskipper gill and skin epithelium using immunohistochemistry and confocal microscopy. Colocalization studies showed that 5-HT is coexpressed with nNOS, Na+/K+-ATPase, TH and VAChT; nNOS is coexpressed with Na+/K+-ATPase and TH in the skin. In the gill 5-HT is coexpressed with nNOS and VAhHT and nNOS is coexpressed with Na+/K+-ATPase and TH. Acetylcholine is also expressed in chain and proximal neurons projecting to the efferent filament artery and branchial smooth muscle. The serotonergic cells c labeled with VAChT, nNOS and TH, thus indicating the presence of NEC populations and the possibility that these neurotransmitters (other than serotonin) may act as primary transmitters in the hypoxic reflex in fish gills. Immunolabeling with TH antibodies revealed that NECs in the gill and the skin are innervated by catecholaminergic nerves, thus suggesting that these cells are involved in a central control of branchial functions through their relationships with the sympathetic branchial nervous system. The Na+/K+-ATPase in mitochondria-rich cells (MRCs), which are most concentrated in the gill lamellar epithelium, is colabeled with nNOS and associated with TH nerve terminals. TH-immunopositive fine varicosities were also associated with the numerous capillaries in the skin surface and the layers of the swollen cells. Based on the often hypercapnic and hypoxic habitat of the mudskippers, these fishes may represent an attractive model for pursuing studies on O2 and CO2 sensing due to the air-breathing that increases the importance of acid/base regulation and the O2-related drive including the function of gasotransmitters such as nitric oxide that has an inhibitory (regulatory) function in ionoregulation.

Functionalized horizontally aligned CNT array and random CNT network for CO2 sensing

Horizontally aligned and density-controlled single-wall carbon nanotubes (CNT) represent attractive building blocks for nanoelectronics. In this paper, horizontally aligned CNT arrays and random CNT network are synthesized by thermal CVD at 925 °C in an ethanol atmosphere. With appropriate functionalization applied to the aligned CNTs, a high sensitivity of 8.48% for ambient CO2 gas concentration of 500 ppm is achieved. In addition, these aligned CNT array sensors show much faster response and recovery time than a random CNT network. Moreover, good selectivity against NO2 and NH3, and good repeatability are demonstrated. These results pave the way for a deeper understanding of the physical and electrical properties of single-wall CNT and inter-tube junctions, which could be helpful in designing and optimizing as-grown single-wall CNT for gas sensor and other nanoelectronic devices.

Ethanol Gas Sensors Composed of Carbon Nanotubes with Au Nanoparticles Adsorbed onto a Flexible PI Substrate

Carbon nanotubes (CNTs) are highly interesting materials for gas sensing. In this study, a simple method of directly transferring high-density CNTs from a SiO2/Si substrate to a flexible substrate for ethanol gas sensing at room temperature was established. The flexible gas sensor exhibited a high sensitivity of 5.39% at room temperature for the ambient ethanol gas concentration of 800 ppm. The gas response of the CNT-based chemiresistor was attributed to p-type conductivity in the Au-modified semiconducting CNTs. Remarkable repeatability of the sensor response to the gas concentration was demonstrated. These results indicated a major step toward the low-cost, large-scale production of this type of device.

Gas exchange in fruits related to skin condition and fruit ripening studied with diode laser spectroscopy.

The concentration of the biologically active molecular oxygen gas is of crucial importance for fruits in the metabolic respiration, maturation, and ripening processes. In our study, oxygen content and oxygen transport in fruits, exemplified by apples and guavas, were studied noninvasively by gas in scattering media absorption spectroscopy. The technique is based on the fact that free gases typically have 10,000 times narrower absorption features than the bulk material. The technique was demonstrated in studies of the influence of the fruit skin in regulating the internal oxygen balance, by observing the signal response of the internal oxygen gas to a transient change in the ambient gas concentration on peeled and unpeeled fruits. In addition, the gas exchange rate at different ripening stages was also studied in intact guavas.

Ignition and formaldehyde formation in dimethyl ether (DME) reacting spray under various EGR levels

As an alternative fuel to diesel in compression-ignition (CI) engines, dimethyl ether (DME) has gained interest in combustion research due to its high cetane number for fast ignition and ultra-low emission of particulate matter. In this study, ignition and important intermediate species including formaldehyde (CH2O) are experimentally investigated in a constant-volume combustion vessel facility that includes a fuel injection system for spray-like behavior of liquid DME. Experiments of different oxygen concentrations simulating various levels of exhaust-gas recirculation (EGR) were performed to study its corresponding effect on the flame structure and emissions from DME combustion. Results from the experiment were then used to validate a 3-D CFD simulation using a detailed chemistry solver. Different stages of ignition characterized by temperature profile, and certain species (e.g., CH2O for cool flame) after start of injection, are provided to conceptualize the DME combustion process under the effect of low-to-high oxygen ambient gas concentrations. Both simulations and experiments showed that there is a supporting link between CH2O formation and low-temperature combustion prior to diffusion-controlled flame uniquely for DME. By studying the temperature and equivalence ratio dependence of the reacting spray at different O2 levels, different stages of ignition along with the formation of CH2O suggested that the start of the depletion of CH2O can be used as an ignition indicator.

Spectacular Oscillations in Plant Isoprene Emission under Transient Conditions Explain the Enigmatic CO2 Response.

Plant isoprene emissions respond to light and temperature similarly to photosynthesis, but CO2 dependencies of isoprene emission and photosynthesis are profoundly different, with photosynthesis increasing and isoprene emission decreasing with increasing CO2 concentration due to reasons not yet understood. We studied isoprene emission, net assimilation rate, and chlorophyll fluorescence under different CO2 and O2 concentrations in the strong isoprene emitter hybrid aspen (Populus tremula × Populus tremuloides), and used rapid changes in ambient CO2 or O2 concentrations or light level to induce oscillations. As isoprene-emitting species support very high steady-state chloroplastic pool sizes of the primary isoprene substrate, dimethylallyl diphosphate (DMADP), which can mask the effects of oscillatory dynamics on isoprene emission, the size of the DMADP pool was experimentally reduced by either partial inhibition of isoprenoid synthesis pathway by fosmidomycin-feeding or by changes in ambient gas concentrations leading to DMADP pool depletion in intact leaves. In feedback-limited conditions observed at low O2 and/or high CO2 concentration under which the rate of photosynthesis is governed by the limited rate of ATP and NADPH formation due to low chloroplastic phosphate levels, oscillations in photosynthesis and isoprene emission were repeatedly induced by rapid environmental modifications in both partly fosmidomycin-inhibited leaves and in intact leaves with in vivo reduced DMADP pools. The oscillations in net assimilation rate and isoprene emission in feedback-inhibited leaves were in the same phase, and relative changes in the pools of photosynthetic metabolites and DMADP estimated by in vivo kinetic methods were directly proportional through all oscillations induced by different environmental perturbations. We conclude that the oscillations in isoprene emission provide direct experimental evidence demonstrating that the response of isoprene emission to changes in ambient gas concentrations is controlled by the chloroplastic reductant supply.

Effects of nitrogen shock treatment on postharvest changes of Yali pears

ABSTRACTThe effects of short-term nitrogen (N2) treatment on fruit quality and respiratory enzymes of Yali pear (Pyrus bretschneideri Rehd.) were investigated. Fruit were N2 shocked by exposing them to N2 for 48 h, and then stored at 0–1°C under ambient atmospheric gas concentrations for 4 months. Results showed that titratable acidity (TA) and total soluble solids (TSS) contents in N2-shocked fruit were higher than those in control fruit. At the end of storage, the core browning rate in N2-shocked fruit was 29.9% lower compared to the control. Alcohol dehydrogenase (ADH) activity was inhibited by N2-shock treatment during the first 90 days of storage. In addition, N2-shocked fruit had lower succinate dehydrogenase (SDH) activity, while cytochrome c oxidase (CCO) activity was induced to high levels compared to the control. N2-shock treatment may be applied as an alternative technology to extend the shelf life of Yali pear fruit.