Search Results (43)

Accessible datasets of greenhouse gas (GHG) concentrations help define long-term trends on a global scale and also provide significant information on the characteristic variability of emission sources and sinks. The integration of stable carbon isotope measurements of carbon dioxide (CO₂) and methane (CH₄) can significantly increase the accuracy and reliability of source apportionment efforts, due to the isotopic fractionation processes and fingerprint that characterize each mechanism. Via isotopic parameters such as δ¹³C, the ratio of ¹³C to ¹²C compared to an international standard (VPDB, Vienna Pee Dee Belemnite), it is in fact possible to discriminate, for example, between thermogenic and microbial sources of CH₄, thus ensuring a more detailed understanding of global balances. A number of stations within the Italian consortium of atmospheric observation sites have been equipped with Picarro G2201-i CRDS (Cavity Ring-Down Spectrometry) analyzers capable of measuring the stable carbon isotopic ratios of CO₂ and CH₄, reported as δ¹³C-CO₂ and δ¹³C-CO₂, respectively. The first dataset (Lamezia Terme, Calabria region) of the consortium resulting from these measurements was released, and a second dataset (Potenza, Basilicata region) from another station was also released, relying on the same format to effectively standardize these new types of datasets. This work provides details on the data, format, and methods used to generate these products and describes a framework for the format and processing of similar data products based on CRD spectroscopy. Full article

The dataset presented in this manuscript consists of three distinct sets of data collected during a laboratory experiment aimed at quantifying the emissions of greenhouse gases (GHGs), specifically methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O). The experiment was conducted in three phases, each initiated at different times. The first phase began on 6 June 2022, using a biocover composed of 60% fine-fraction waste, 20% clay soil, and 20% stabilized compost. The second phase commenced on 26 August 2022, with two biocover variants: one composed of 50% fine-fraction waste and 50% clay soil, and the other consisting of 40% fine-fraction waste, 40% clay soil, and 20% shredded paper. The final phase started on 27 October 2022, introducing two biocovers: one containing 25% dried algae, 25% fine-fraction waste, 25% gravel (0–20 mm), and 25% ash, and the other composed of 40% fine-fraction waste, 40% dried algae, and 20% chernozem. Emission assessments were conducted three weeks after the biocover installation to allow for settling and stabilization, followed by weekly measurements two to three days before irrigation with 250 mL of water to simulate field conditions. GHG emission quantification was carried out using the Cavity Ring-Down Spectroscopy gas measurement device, Picarro G2508. This dataset offers substantial scientific value for advancing biocover technologies aimed at reducing GHG emissions in landfill environments, particularly for mitigating methane emissions. In addition to initial experimental use, the dataset offers a wide range of possibilities for reuse, including modeling landfill gas emissions, validating gas flow measurement methods, developing machine learning models, and performing meta-analyses. Its detailed structure facilitates multi-faceted environmental research and supports optimization of landfill management. Full article

Rapid and precise detection of hydrogen sulfide (H₂S) at trace levels is critical for industrial safety and environmental air quality monitoring, yet existing methods often struggle with cost, speed, or sensitivity. A cost-effective cavity ring-down spectroscopy (CRDS) analyzer is presented, incorporating a novel digital locking circuit for sequential laser-cavity mode matching. This system demonstrates rapid and precise hydrogen sulfide (H₂S) detection capability at parts-per-billion (ppb) concentration levels. Compared to traditional wavelength meters, our system delivers a 140-fold improvement in frequency interval precision (0.07 MHz, 0.027% relative uncertainty). Allan variance analysis under vacuum conditions demonstrates a sensitivity limit of 3 × 10⁻¹² cm⁻¹ at a 60-s averaging time. Validated through calibrated gas dilution tests, the analyzer detects a 4 ppb H₂S absorption signal with a signal-to-noise ratio (SNR) > 6, establishing a 2 ppb detection limit (3σ criterion). This innovative approach meets stringent industrial and environmental requirements, offering a significant advancement in trace gas-sensing technology. Full article

We present an empirical model for the cross-section of low concentration acetone gas in the range of 1671.5–1675 nm that encompasses the absorption band of the methyl stretch overtone. This model is experimentally validated with cavity ring-down spectroscopy (CRDS) measurements performed with a calibration gas and its diluted mixtures with breath samples. Particular attention is paid to accurate wavelength measurements with an interferometric wavemeter. The theoretical framework for analysis of gas mixtures with several absorbing species is presented. We show that the proposed empirical model can be used to accurately determine the concentration of acetone vapor in human breath samples. The comparison of the acetone absorption cross-section with previous results is also presented. Full article

Hydrogen purity plays a crucial role in the expanding hydrogen economy, particularly in applications such as fuel cells and industrial processes. This review investigates the relationship between hydrogen production methods and resulting purity levels, emphasizing the differences between reforming, electrolysis, and biomass-based techniques. Furthermore, it explores state-of-the-art purification technologies, including pressure swing adsorption (PSA), membrane separation, and cryogenic distillation, highlighting their effectiveness and limitations in achieving ultra-pure hydrogen. Analytical methods such as gas chromatography, mass spectrometry, and cavity ring-down spectroscopy are also discussed in terms of their accuracy and application scope for hydrogen quality assessment. By integrating findings from global and domestic studies, this paper aims to provide a comprehensive understanding of the challenges and advancements in hydrogen purity, offering insights into optimizing hydrogen for a sustainable energy future. Full article

The monitoring of acetone in exhaled breath is expected to provide a noninvasive and painless method for dynamic monitoring of summarized physiological metabolic status during obesity treatment. Although the commonly used Mass Spectrometry (MS) technology has high accuracy, the long detection time and large equipment size limit the application of daily bedside detection. As for the real-time and accurate detection of acetone, the gas sensor has become the best choice of gas detection technology, but it is easy to be disturbed by water vapor in breath gas. An integrated breath gas detection system based on cavity ring-down spectroscopy (CRDS) is reported in this paper, which is a laser absorption spectroscopy technique with high-sensitivity detection and absolute quantitative analysis. The system uses a 266 nm single-wavelength ultraviolet laser combined with a breath gas pretreatment unit to effectively remove the influence of water vapor. The ring-down time of this system was 1.068 μs, the detection sensitivity was 1 ppb, and the stability of the system was 0.13%. The detection principle of the integrated breath gas detection system follows Lambert–Beer’s law, which is an absolute measurement with very high detection accuracy, and was further validated by Gas Chromatography–Mass Spectrometer (GC-MS) testing. Significant differences in the response of the integrated breath gas detection system to simulated gases containing different concentrations of acetone indicate the potential of the system for the detection of trace amounts of acetone. Meanwhile, the monitoring of acetone during obesity treatment also signifies the feasibility of this system in the dynamic monitoring of physiological indicators, which is not only important for the optimization of the obesity treatment process but also promises to shed further light on the interaction between obesity treatment and physiological metabolism in medicine. Full article

The present study addresses advanced monitoring techniques for particles and airborne molecular contaminants (AMCs) in cleanroom environments, which are crucial for ensuring the integrity of semiconductor manufacturing processes. We focus on quantifying particle levels and a representative AMC, hydrogen chloride (HCl), having known detrimental effects on equipment longevity, product yield, and human health. We have developed a compact laser sensor based on open-path cavity ring-down spectroscopy (CRDS) using a 1742 nm near-infrared diode laser source. The sensor enables the high-sensitivity detection of HCl through absorption by the 2-0 vibrational band with an Allan deviation of 0.15 parts per billion (ppb) over 15 min. For quantifying particle number concentrations, we examine various detection methods based on statistical analyses of Mie scattering-induced ring-down time fluctuations. We find that the ring-down distributions’ 3rd and 4th standard moments allow particle detection at densities as low as ~10⁵ m⁻³ (diameter > 1 μm). These findings provide a basis for the future development of compact cleanroom monitoring instrumentation for wafer-level monitoring for both AMC and particles, including mobile platforms. Full article

Quantifying and controlling fugitive methane emissions from oil and gas facilities remains essential for addressing climate goals, but the costs associated with monitoring millions of production sites remain prohibitively expensive. Current thinking, supported by measurement and simple dispersion modelling, assumes single-digit parts-per-million instrumentation is required. To investigate instrument response, the inlets of three trace-methane (sub-ppm) analyzers were collocated on a facility designed to release gas of known composition at known flow rates between 0.4 and 5.2 kg CH₄ h⁻¹ from simulated oil and gas infrastructure. Methane mixing ratios were measured by each instrument at 1 Hertz resolution over nine hours. While mixing ratios reported by a cavity ring-down spectrometer (CRDS)-based instrument were on average 10.0 ppm (range 1.8 to 83 ppm), a mid-infrared laser absorption spectroscopy (MIRA)-based instrument reported short-lived mixing ratios far larger than expected (range 1.8 to 779 ppm) with a similar nine-hour average to the CRDS (10.1 ppm). We suggest the peaks detected by the MIRA are likely caused by a micrometeorological phenomenon, where vortex shedding has resulted in heterogeneous methane plumes which only the MIRA can observe. Further analysis suggests an instrument like the MIRA (an optical-cavity-based instrument with cavity size ≤10 cm³ measuring at ≥2 Hz with air flow rates in the order of ≤0.3 slpm at distances of ≤20 m from the source) but with a higher detection limit (25 ppm) could detect enough of the high-concentration events to generate representative 20 min-average methane mixing ratios. Even though development of a lower-cost, high-precision, high-accuracy instrument with a 25 ppm detection threshold remains a significant problem, this has implications for the use of instrumentation with higher detection thresholds, resulting in the reduction in cost to measure methane emissions and providing a mechanism for the widespread deployment of effective leak detection and repair programs for all oil and gas infrastructure. Full article

Stable isotopes of water (δ²H and δ¹⁸O) are reliable tracers for the investigation of plant–soil–water interactions in forest ecosystems. However, variations in isotopic compositions may arise due to differences in analytical instruments and water extraction methods. In this study, we conducted three different experiments to identify isotopic differences caused by analytical and methodological variations. First, we analyzed soil water by using the two most commonly applied methods: isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS). Second, we compared the isotopes in xylem water extracted from the stems of nine tree species using cryogenic vacuum distillation (CVD) with different heating times. Third, we compared the compositions in xylem water extracted with three different methods: mechanical squeezing using a pressure chamber (PC), an induction module (IM), and CVD. The differences in isotopic composition between IRMS and CRDS were significant but minimal. Soil properties were not significant factors contributing to differences between the two instruments. For the xylem water extraction with CVD, each of the nine tree species required heating for more than three hours. Significant differences were observed in δ²H among the three extraction methods for xylem water. Xylem water extracted by CVD showed more depleted values compared to those obtained by PC and IM. Our results highlight the importance of considering analytical and methodological variations in stable isotope analysis. Full article

Formaldehyde (HCHO) is a tracer of volatile organic compounds (VOCs), and its concentration has gradually decreased with the reduction in VOC emissions in recent years, which puts forward higher requirements for the detection of trace HCHO. Therefore, a quantum cascade laser (QCL) with a central excitation wavelength of 5.68 μm was applied to detect the trace HCHO under an effective absorption optical pathlength of 67 m. An improved, dual-incidence multi-pass cell, with a simple structure and easy adjustment, was designed to further improve the absorption optical pathlength of the gas. The instrument detection sensitivity of 28 pptv (1σ) was achieved within a 40 s response time. The experimental results show that the developed HCHO detection system is almost unaffected by the cross interference of common atmospheric gases and the change of ambient humidity. Additionally, the instrument was successfully deployed in a field campaign, and it delivered results that correlated well with those of a commercial instrument based on continuous wave cavity ring-down spectroscopy (R² = 0.967), which indicates that the instrument has a good ability to monitor ambient trace HCHO in unattended continuous operation for long periods of time. Full article

In the past, climate change led the United Nations to define the Sustainable Development Goals Statement “blueprint to achieve a better and more sustainable future” and the European Commission to promote the “bioeconomy” concept and to launch the Green Deal Policy. Accordingly, the COP26 conference proposed a drastic reduction of fossil-based fuels and materials, in favor of biobased materials which should ensure intrinsic carbon neutrality. Contextually, many startups and established materials suppliers proposed new, trendy materials claiming sustainability advantages but, in many cases, without robust scientific backing. The need for transparency in terms of circularity led us to exploit a fast, reliable and easily deployable analytical method for assessing the biogenic carbon fraction in a variety of industrial materials. Our research team identified a radiocarbon analysis based on Saturated-absorption CAvity Ring-down (SCAR) spectroscopy as a quick and effective method for such a scope. Here we demonstrate its use for the determination of biogenic/fossil carbon proportions of polymeric and coated materials such as leather, coated textiles and trendy alternatives used in the fashion industry, with the scope of defining their intrinsic renewable content. The reliability of the SCAR method is validated through a comparison with the results obtained by the benchmark technique. Full article

Methane is the most frequently analyzed gas with different concentrations ranging from single ppm or ppb to 100%. There are a wide range of applications for gas sensors including urban uses, industrial uses, rural measurements, and environment monitoring. The most important applications include the measurement of anthropogenic greenhouse gases in the atmosphere and methane leak detection. In this review, we discuss common optical methods used for detecting methane such as non-dispersive infrared (NIR) technology, direct tunable diode spectroscopy (TDLS), cavity ring-down spectroscopy (CRDS), cavity-enhanced absorption spectroscopy (CEAS), lidar techniques, and laser photoacoustic spectroscopy. We also present our own designs of laser methane analyzers for various applications (DIAL, TDLS, NIR). Full article

Accurate accounting of the partition between anthropogenic and biogenic carbon dioxide mixing ratios (CO_2Anth and CO_2Bio) in urban-based CO₂ measurements is key to developing effective emission reduction strategies since such measurements can provide an independent catalogue of local and regional CO₂ emission inventories. In an attempt to delineate the contribution of CO_2Bio to the overall urban CO₂ mixing ratio enhancements, carbon monoxide (CO) was utilized as a tracer, following CO₂ and CO mixing ratio measurements using a wavelength-scanned cavity ring-down spectrometer (CRDS). These measurements were performed in Cookeville, TN, (36.1628° N, 85.5016° W), a medium-sized city within the Eastern Highland Rim region of the United States. Between the years 2017 and 2019, the average seasonal wintertime CO_2Bio mixing ratios varied between −0.65 ± 3.44 ppm and 0.96 ± 2.66 ppm. During the springtime, the observed CO_2Bio signals were largely negative while the CO_2Anth values were generally lower than the wintertime values. The contribution of CO from the isoprene oxidation reaction with the hydroxyl radical (OH) (CO_isoprene) to the overall CO enhancement during the growing season was estimated to be ~17–27 ppb, underscoring the importance of considering the contribution of CO_isoprene to untangling different CO_2Anth and CO_2Bio sources and sinks in high isoprene-emitting urban environments. Full article

This work communicates cavity ring-down spectroscopy (CRDS) of methylidyne (CH) in a chemiluminescent plasma that is produced in a microwave cavity. Of interest are the rotational lines of the 0-0 vibrational transition for the A–X band and the 1-0 vibrational transition for the B–X band. The reported investigations originate from research on the CH radical in 1996, which constituted the first case of applying CRDS to the CH radical. The report also includes a recent analysis that shows excellent agreement of the measured and computed data, and it communicates CH line strength data. The CH radical is an important diatomic molecule in hydrocarbon combustion diagnosis and the analysis of stellar plasma emissions, to name just two examples of analytical plasma chemistry. Full article

A sensitive, compact detector for the simultaneous measurement of O₃ and NO₂ is presented in this work. There are two channels in the detector, namely the O_x channel and the NO₂ channel. In the presence of excess NO, ambient O₃ is converted to NO₂ in the O_x measurement channel. In both channels, NO₂ is directly detected via cavity ring-down spectroscopy (CRDS) at 409 nm. At a 10 s integration time, the O_x and NO₂ channels have a 1σ precision of 14.5 and 13.5 pptv, respectively. The Allan deviation plot shows that the optimal sensitivity of O₃ and NO₂ occurs at an integration time of ~60 s, with values of 10.2 and 8.5 pptv, respectively. The accuracy is 6% for the O₃ channel and 5% for the NO₂ channel, and the largest uncertainty comes from the effective NO₂ absorption cross-section. Intercomparison of the NO₂ detection between the NO₂ and O_x channels shows good agreement within their uncertainties, with an absolute shift of 0.31 ppbv, a correlation coefficient of R² = 0.99 and a slope of 0.98. Further intercomparison for ambient O₃ measurement between the O₃/NO₂-CRDS developed in this work and a commercial UV O₃ monitor also shows excellent agreement, with linear regression slopes close to unity and an R² value of 0.99 for 1 min averaged data. The system was deployed to measure O₃ and NO₂ concentrations in Hefei, China, and the observation results show obvious diurnal variation characteristics. The successful deployment of the system has demonstrated that the instrument can provide a new method for retrieving fast variations in ambient O₃ and NO₂. Full article