This article presents a literature review of sensors for the monitoring of benzene in ambient air and other volatile organic compounds. Combined with information provided by stakeholders, ...manufacturers and literature, the review considers commercially available sensors, including PID-based sensors, semiconductor (resistive gas sensors) and portable on-line measuring devices as for example sensor arrays. The bibliographic collection includes the following topics: sensor description, field of application at fixed sites, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions.
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Preparation of accurate reference gas standards at low amount fractions such as for greenhouse gases requires highly sensitive instrumentation to determine the purity of the gases used in the ...preparation. For this purpose, a versatile CRDS spectrometer has been constructed at VSL based on high-power, continuous wave OPOs covering a very wide wavelength range of 2.3–5.1 µm. Due to the use of passivated materials, the spectrometer is also suitable for the measurement of reactive impurities. Details of the spectrometer are presented together with several examples of purity analysis.
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Different forms of nitrogen (N) fertilizer affect disease development; however, this study investigated the effects of N forms on the hypersensitivity response (HR)—a pathogen-elicited cell death ...linked to resistance. HR-eliciting Pseudomonas syringae pv. phaseolicola was infiltrated into leaves of tobacco fed with either Formula or Formula. The speed of cell death was faster in Formula-fed compared with Formula-fed plants, which correlated, respectively, with increased and decreased resistance. Nitric oxide (NO) can be generated by nitrate reductase (NR) to influence the formation of the HR. NO generation was reduced in Formula-fed plants where N assimilation bypassed the NR step. This was similar to that elicited by the disease-forming P. syringae pv. tabaci strain, further suggesting that resistance was compromised with Formula feeding. PR1a is a biomarker for the defence signal salicylic acid (SA), and expression was reduced in Formula-fed compared with Formula fed plants at 24h after inoculation. This pattern correlated with actual SA measurements. Conversely, total amino acid, cytosolic and apoplastic glucose/fructose and sucrose were elevated in Formula- treated plants. Gas chromatography/mass spectroscopy was used to characterize metabolic events following different N treatments. Following Formula nutrition, polyamine biosynthesis was predominant, whilst after Formula nutrition, flux appeared to be shifted towards the production of 4-aminobutyric acid. The mechanisms whereby Formula feeding enhances SA, NO, and polyamine-mediated HR-linked defence whilst these are compromised with Formula, which also increases the availability of nutrients to pathogens, are discussed.
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The absence of contaminants in the hydrogen delivered at the hydrogen refuelling station is critical to ensure the length life of FCEV. Hydrogen quality has to be ensured according to the two ...international standards ISO 14687–2:2012 and ISO/DIS 19880-8. Amount fraction of contaminants from the two hydrogen production processes steam methane reforming and PEM water electrolyser is not clearly documented. Twenty five different hydrogen samples were taken and analysed for all contaminants listed in ISO 14687-2. The first results of hydrogen quality from production processes: PEM water electrolysis with TSA and SMR with PSA are presented. The results on more than 16 different plants or occasions demonstrated that in all cases the 13 compounds listed in ISO 14687 were below the threshold of the international standards. Several contaminated hydrogen samples demonstrated the needs for validated and standardised sampling system and procedure. The results validated the probability of contaminants presence proposed in ISO/DIS 19880-8. It will support the implementation of ISO/DIS 19880-8 and the development of hydrogen quality control monitoring plan. It is recommended to extend the study to other production method (i.e. alkaline electrolysis), the HRS supply chain (i.e. compressor) to support the technology growth.
•No contaminants above ISO 14687-2 threshold in H2 from SMR with PSA.•No contaminants above ISO 14687-2 threshold in H2 from PEMW with TSA.•Impact of TSA on contaminants from PEMW electrolyser.•Sampling contamination may lead to false positive.•Probability of contaminants presence in line with real hydrogen samples.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Over the past 10 years, with the advent of new crystals designs and a new generation of pump lasers, continuous‐wave (cw) optical parametric oscillators (OPOs) have developed into mature ...monochromatic light sources. Nowadays, cw OPOs can fulfill a wide variety of criteria for sensitive molecular gas sensing. It can access the mid‐infrared wavelength region, where many molecules have their fundamental rotational‐vibrational transitions, with high power. This high power combined with wide wavelength tuning and narrow linewidth creates excellent conditions for sensitive, high‐resolution spectroscopy. OPOs combined with robust methods, such as photoacoustic spectroscopy and cavity‐enhanced spectroscopy, are well suited for field measurements and remote‐sensing applications. The wide tunability of cw OPOs allows detection of larger molecules with broad absorption band structures, and its fast scanning capabilities allow rapid detection of trace gases, the latter is a demand for life‐science applications. After a short introduction about the physical principle of cw OPOs, with its most recent physical developments, this review focuses on sensitive molecular gas sensing with a variety of spectroscopic applications in atmospheric and life sciences.
Over the past 10 years, with the advent of new crystals designs and a new generation of pump lasers, continuous‐wave (cw) optical parametric oscillators (OPOs) have developed into mature monochromatic light sources. Nowadays, cw OPOs can fulfill a wide variety of criteria for sensitive molecular gas sensing. It can access the mid‐infrared wavelength region, where many molecules have their fundamental rotational‐vibrational transitions, with high power. This high power combined with wide wavelength tuning and narrow linewidth creates excellent conditions for sensitive, high‐resolution spectroscopy. OPOs combined with robust methods, such as photoacoustic spectroscopy and cavity‐enhanced spectroscopy, are well suited for field measurements and remote‐sensing applications. The wide tunability of cw OPOs allows detection of larger molecules with broad absorption band structures, and its fast scanning capabilities allow rapid detection of trace gases, the latter is a demand for life‐science applications. After a short introduction about the physical principle of cw OPOs, with its most recent physical developments, this review focuses on sensitive molecular gas sensing with a variety of spectroscopic applications in atmospheric and life sciences.
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Gaseous hydrogen for fuel cell electric vehicles must meet quality standards such as ISO 14687:2019 which contains maximal control thresholds for several impurities which could damage the fuel cells ...or the infrastructure. A review of analytical techniques for impurities analysis has already been carried out by Murugan et al. in 2014. Similarly, this document intends to review the sampling of hydrogen and the available analytical methods, together with a survey of laboratories performing the analysis of hydrogen about the techniques being used. Most impurities are addressed, however some of them are challenging, especially the halogenated compounds since only some halogenated compounds are covered, not all of them. The analysis of impurities following ISO 14687:2019 remains expensive and complex, enhancing the need for further research in this area. Novel and promising analyzers have been developed which need to be validated according to ISO 21087:2019 requirements.
The Tropospheric Monitoring Instrument (TROPOMI) is the single instrument on board the ESA Copernicus Sentinel-5 Precursor satellite. TROPOMI is a nadir-viewing imaging spectrometer with bands in the ...ultraviolet and visible, the near infrared and the shortwave infrared (SWIR). An accurate instrument spectral response function (ISRF) is required in the SWIR band where absorption lines of CO, methane and water vapor overlap. In this paper, we report on the determination of the TROPOMI-SWIR ISRF during an extensive on-ground calibration campaign. Measurements are taken with a monochromatic light source scanning the whole detector, using the spectrometer itself to determine the light intensity and wavelength. The accuracy of the resulting ISRF calibration key data is well within the requirement for trace-gas retrievals. Long-term in-flight monitoring of SWIR ISRF is achieved using five on-board diode lasers.
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The shortwave infrared (SWIR) spectrometer module of the Tropospheric
Monitoring Instrument (TROPOMI), on board the ESA Copernicus Sentinel-5
Precursor satellite, is used to measure atmospheric CO ...and methane columns.
For this purpose, calibrated radiance measurements are needed that are
minimally contaminated by instrumental stray light. Therefore, a method has
been developed and applied in an on-ground calibration campaign to
characterize stray light in detail using a monochromatic quasi-point light
source. The dynamic range of the signal was extended to more than 7 orders of magnitude by performing measurements with different exposure times,
saturating detector pixels at the longer exposure times. Analysis of the
stray light indicates about 4.4 % of the detected light is correctable stray
light. An algorithm was then devised and implemented in the operational data
processor to correct in-flight SWIR observations in near-real time, based on
Van Cittert deconvolution. The stray light is approximated by a far-field
kernel independent of position and wavelength and an additional kernel
representing the main reflection. Applying this correction significantly
reduces the stray-light signal, for example in a simulated dark forest scene
close to bright clouds by a factor of about 10. Simulations indicate that
this reduces the stray-light error sufficiently for accurate gas-column
retrievals. In addition, the instrument contains five SWIR diode lasers that
enable long-term, in-flight monitoring of the stray-light distribution.
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Nitrogenase activity, indicative of N2 fixation, was measured in the surface waters along a north-south transect in the eastern Atlantic Ocean, from Texel (The Netherlands, $53\textdegree N$) to Cape ...Town (South Africa, $35\textdegree S$) using a sensitive on-line, near real-time acetylene reduction assay. From the beginning of January to the end of February 2000 nitrogenase activity was detected in varying rates, but only between $14\textdegree N$ and $13\textdegree S$ latitudes. Dark incubations yielded an average activity of $2.2 (\pm 2.4) \mu mol m^{-2} d^{-1} N$, but light increased the activity to $3.7 (\pm 2.9) \mu mol m^{-2} d^{-1}$ N. However, nitrogenase activity in the light was sensitive to O2 doubling to $7.6 (\pm 12.7) \mu mol m^{-2} d^{-1}$ N when the incubation was anaerobic. In the area where N2 fixation occurred, phosphate concentrations were fourfold lower than in the area where N2 fixation was absent, while silicate levels were higher. The water temperature in the area with N2 fixation was $28\textdegree C$, while in the adjacent area the temperature was $3\textdegree C$ lower, which might have prevented the proliferation of diazotrophic cyanobacteria. Action spectra revealed that chlorophyll a, phycocyanin, and phycoerythrin are the light-harvesting pigments supporting nitrogenase activity. In one area in the northern latitudes, potential nitrogenase activity was highest during daytime, which is characteristic for Trichodesmium. In areas with a high potential nitrogenase activity, surface waters were dominated by a phycoerythrin-containing cyanobacterium. Since nitrogenase activities were highest at night, these cells may have been unicellular cyanobacteria like Crocosphaera.
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BACKGROUND AND AIMS: The relationship between ethylene production and both seed dormancy and germination was investigated using red rice (weedy rice) as a model species. METHODS: Both fully dormant ...and after-ripened (non-dormant) naked caryopses were incubated with or without inhibitors of ethylene synthesis aminoethoxyvinylglycine (AVG) and perception silver thiosulfate (STS), or in the presence of the natural ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of ethylene emissions were measured with a sensitive laser-photoacoustic system. KEY RESULTS: Dormant red rice caryopses did not produce ethylene. In non-dormant caryopses, ethylene evolution never preceded the first visible stage of germination (pericarp splitting), and ethylene inhibitors completely blocked ethylene production, but not pericarp splitting. Accordingly, endogenous ACC appeared to be lacking before pericarp splitting. However, early seedling growth (radicle or coleoptile attaining the length of 1 mm) followed ethylene evolution and was delayed by the inhibitors. Wounding the dormant caryopses induced them to germinate and produce ethylene, but their germination was slow and pericarp splitting could be speeded up by ethylene. CONCLUSIONS: The findings suggest that, in red rice, endogenous ethylene stimulates the growth of the nascent seedling, but does not affect seed dormancy or germination inception. Correspondingly, this phytohormone does not play a role in the dormancy breakage induced by wounding, but accelerates germination after such breakage has occurred.
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