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Over 900 event-based precipitation samples were collected in 2019–2021 in the Tien Shan and its foothills and analysed using cavity ring-down spectroscopy. δ D and δ18 O values were highest in summer and lowest in winter, and annual cycles of deuterium excess (d-excess) varied between sites, reflecting local conditions. The δ18 O and δ D values increased from north to south in all seasons except autumn, and latitude was a statistically significant predictor of δ18 O and δ D in the overall data set, along with elevation in winter and elevation and longitude in autumn. Elevation was a significant predictor of d-excess in all seasons, and local air temperature was a more important control over δ18 O and δ D than precipitation depth. Local meteoric water lines were derived using seven regression methods applied to non-weighted and weighted precipitation. Non-weighted ordinary least squares regression and reduced major axis regression methods are recommended overall, except for summer when the precipitation-weighted least squares regression should be used, particularly in the south. Atmospheric back-trajectory and mixing-model analyses were applied in combination to identify air mass source regions and their relative contribution to precipitation. Recycled moisture from irrigated land in the Amu Darya and Syr Darya basins and from the study catchments accounted for 29 %–71 % of precipitation, depending on the site and season. In the Chon Kyzyl-Suu catchment, local re-evaporation from Issyk-Kul accounted for up to 85 % of precipitation. These findings highlight the importance of moisture from terrestrial sources, especially irrigated land, for the formation of precipitation in the Tien Shan. [ABSTRACT FROM AUTHOR]

Fluid inclusions are a window into deep geological fluids, providing unique access to their nature and composition. The isotopic composition of CO2 and CH4 hosted in fluid inclusions is a powerful proxy to assess the origin and transformation of deep geological fluids, giving insights into carbon sources, fluxes, and degassing in a wide variety of geodynamic settings. Over the last 5 decades, techniques have been developed to extract fluid inclusions from their host minerals and measure their bulk composition. These techniques are often challenged by analytical artifacts including high blank levels of CO2 and CH4, fluid re-speciation, gas adsorption, and diffusion. Since these processes may alter the pristine composition of gases liberated from fluid inclusions, rigorous protocols are needed in order to evaluate the isotopic integrity of the extracted volatile species. In this study, we introduce new protocols for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 and δ13C-CO2 using a Cavity Ring-Down Spectroscopy (CRDS) analyser (Picarro G2201-i). Two mechanical fluid extraction techniques are compared: ball milling in ZrO2 jars and sample crushing in a stainless steel sealed tube under a hydraulic press. Blanks and isotopically labelled tests with the ball milling technique suggest that rotation speed, grinding stock filling degree and filling type alter the CH4 and CO2 concentrations and isotopic compositions measured by the CRDS analyser. In contrast, the crushing technique does not generate measurable quantities of blank CH4 and CO2. The protocols presented in this study allow to extract, detect, and analyse δ13C of CH4 and CO2 for concentrations above 10 and 1,000 ppm respectively. Interlaboratory experiments allowed to replicate previously measured δ13C-CH4 values in natural fluid inclusions within 1‰ with both extraction techniques. This study highlights the potential of combining simple bulk off-line fluid inclusion extraction techniques with a CRDS analyser for δ13C analysis of CO2 and CH4 without gas separation being required. [ABSTRACT FROM AUTHOR]

Accurate estimates of greenhouse gas emissions and sinks are critical for understanding the carbon cycle and identifying key drivers of anthropogenic climate change. In this study, we investigate the variability in CO and CO2 concentrations and their ratio over the Mexico City metropolitan area (MCMA) using long-term, time-resolved columnar measurements at three stations, employing solar-absorption Fourier transform infrared spectroscopy (FTIR). Using a simple model and the mixed-layer height derived from a ceilometer, we determined the CO and CO2 concentrations in the mixed layer from the total column measurements and found good agreement with surface cavity ring-down spectroscopy measurements. In addition, we used the diurnal pattern of CO columnar measurements at specific time intervals to estimate an average growth rate that, when combined with the space-based Tropospheric Monitoring Instrument (TROPOMI) CO measurements, allowed for the derivation of annual CO and CO2 MCMA emissions from 2016 to 2021. A CO emission decrease of more than 50 % was found during the COVID-19 lockdown period with respect to the year 2018. These results demonstrate the feasibility of using long-term EM27/SUN column measurements to monitor the annual variability in the anthropogenic CO2 and CO emissions in Mexico City without recourse to complex transport models. This simple methodology could be adapted to other urban areas if the orography of the regions favours low ventilation for several hours per day and the column growth rate is dominated by the emission flux. [ABSTRACT FROM AUTHOR]

To effectively monitor highly heterogeneous urban CO2 emissions using atmospheric observations, there is a need to deploy cost-effective CO2 sensors at multiple locations within the city with sufficient accuracy to capture the concentration gradients in urban environments. These dense measurements could be used as input of an atmospheric inversion system for the quantification of emissions at the sub-city scale or to separate specific sectors. Such quantification would offer valuable insights into the efficacy of local initiatives and could also identify unknown emission hotspots that require attention. Here we present the development and evaluation of a mid-cost CO2 instrument designed for continuous monitoring of atmospheric CO2 concentrations with a target accuracy of 1 ppm for hourly mean measurements. We assess the sensor sensitivity in relation to environmental factors such as humidity, pressure, temperature and CO2 signal, which leads to the development of an effective calibration algorithm. Since July 2020, eight mid-cost instruments have been installed within the city of Paris and its vicinity to provide continuous CO2 measurements, complementing the seven high-precision cavity ring-down spectroscopy (CRDS) stations that have been in operation since 2016. A data processing system, called CO2calqual, has been implemented to automatically handle data quality control, calibration and storage, which enables the management of extensive real-time CO2 measurements from the monitoring network. Colocation assessments with the high-precision instrument show that the accuracies of the eight mid-cost instruments are within the range of 1.0 to 2.4 ppm for hourly afternoon (12:00–17:00 UTC) measurements. The long-term stability issues require manual data checks and instrument maintenance. The analyses show that CO2 measurements can provide evidence for underestimations of CO2 emissions in the Paris region and a lack of several emission point sources in the emission inventory. Our study demonstrates promising prospects for integrating mid-cost measurements along with high-precision data into the subsequent atmospheric inverse modeling to improve the accuracy of quantifying the fine-scale CO2 emissions in the Paris metropolitan area. [ABSTRACT FROM AUTHOR]

In this study, we report highly precise and accurate measurements of the P(5), P(6), and O(3) transitions of the 2-0 band of HD occurring at approximately 1.5 µm. HD spectra were acquired in the pressure range of 100-900 Torr using a cavity ring-down spectrometer linked to an optical frequency comb. The line-shape analysis was performed using the Hartmann-Tran profile in the so-called β-corrected version. For the P(5) transition, we improved the accuracy of previous line center frequency determinations by more than two orders of magnitude. Moreover, for the P(5) and P(6) line centers, the total standard uncertainty is below 3 MHz, similar to those provided by quantum electrodynamics predictions, making them useful for direct comparisons that might foster future improvements of the theoretical model. [ABSTRACT FROM AUTHOR]

Cryptochrome 4a (Cry4a) has been proposed as the sensor at the heart of the magnetic compass in migratory songbirds. Blue-light excitation of this protein produces magnetically sensitive flavin–tryptophan radical pairs whose properties suggest that Cry4a could indeed be suitable as a magnetoreceptor. Here, we use cavity ring-down spectroscopy to measure magnetic field effects on the kinetics of these radical pairs in modified Cry4a proteins from the migratory European robin and from nonmigratory pigeon and chicken. B1/2, a parameter that characterizes the magnetic field-dependence of the reactions, was found to be larger than expected on the basis of hyperfine interactions and to increase with the delay between pump and probe laser pulses. Semiclassical spin dynamics simulations show that this behavior is consistent with a singlet–triplet dephasing (STD) relaxation mechanism. Analysis of the experimental data gives dephasing rate constants, rSTD, in the range 3–6 × 107 s−1. A simple "toy" model due to Maeda, Miura, and Arai [Mol. Phys. 104, 1779–1788 (2006)] is used to shed light on the origin of the time-dependence and the nature of the STD mechanism. Under the conditions of the experiments, STD results in an exponential approach to spin equilibrium at a rate considerably slower than rSTD. We attribute the loss of singlet–triplet coherence to electron hopping between the second and third tryptophans of the electron transfer chain and comment on whether this process could explain differences in the magnetic sensitivity of robin, chicken, and pigeon Cry4a's. [ABSTRACT FROM AUTHOR]

• A novel system for directly measuring net photochemical ozone production rates in the atmosphere was developed. • A comparison of P(O 3) was conducted between the directly measured and calculated based on radical reactions. • The instrument was successfully deployed for the comprehensive field observation at an urban site in Yangtze River Delta (China) for 40 days. A novel system for measuring net photochemical ozone production rates in the atmosphere based on cavity ring-down spectroscopy (OPR-CRDS) was developed. The system consists of two chambers (a reaction chamber and a reference chamber) and a dual-channel O x -CRDS detector. To minimize the wall loss of O x in the chambers, the inner surfaces of both chambers are coated with Teflon film. The performance of the OPR-CRDS system was characterized. It was found that even though the photolysis frequency (J value) decreased by 10%, the decrease in the P(O 3) caused by the ultraviolet-blocking film coating was less than 3%. The two chambers had a good consistency in the mean residence time and the measurement of NO 2 and O x under the condition of no sunlight. The detection limit of the OPR-CRDS was determined to be 0.20 ppbv/hr. To further verify the accuracy of the system, the direct measurement values of the OPR-CRDS system were compared with the calculation results based on radical (OH, HO 2 , and RO 2) reactions, and a good correlation was obtained between the measured and calculated values. Finally, the developed instrument was applied to obtain the comprehensive field observations at an urban site in the Yangtze River Delta (China) for 40 days, the time series and change characteristics of the P(O 3) were obtained directly, and the good environmental adaptability and stability of the OPR-CRDS system were demonstrated. It is expected that the new instrument will be beneficial to investigations of the relationship between P(O 3) and its precursors. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is a pyramidal symmetric top molecule with inversion motion and it exists in two distinct nuclear spin isomeric forms, ortho-NH3 (K = 3n) and para-NH3 (K ≠ 3n). Here, a pair of electric dipole-allowed [RQ(4,3) and PP(2,2)] and weak forbidden [OP(3,3) and SQ(8,1)] transitions of gas-phase NH3 were probed in the ν4 fundamental vibrational band occurring at 6.2 µm mid-IR interference-free spectral region using an external-cavity quantum cascade laser coupled cavity ring-down spectrometer. We have experimentally achieved the ortho-to-para ratio (OPR) of (1.03 ± 0.24) and (1.08 ± 0.14) at room temperature (296 K) for the allowed and forbidden transitions of NH3, respectively. Furthermore, our experimental findings confirm that the nuclear spin-symmetry is conserved under the nonreactive perturber-induced collisional processes. This study paves the way to directly probe the nuclear spin-isomers of gas-phase NH3 and thus may lead to an in-depth understanding of nuclear spin-isomerism associated with various physical and chemical processes. This work shows the high-resolution probing of ortho- and para-nuclear spin-isomers of NH3 in the gas phase at room temperature using quantum cascade laser coupled cavity ring-down spectroscopy at 6.2 µm mid-IR spectral region. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is a pyramidal symmetric top molecule with inversion motion and it exists in two distinct nuclear spin isomeric forms, ortho-NH3 (K = 3n) and para-NH3 (K ≠ 3n). Here, a pair of electric dipole-allowed [RQ(4,3) and PP(2,2)] and weak forbidden [OP(3,3) and SQ(8,1)] transitions of gas-phase NH3 were probed in the ν4 fundamental vibrational band occurring at 6.2 µm mid-IR interference-free spectral region using an external-cavity quantum cascade laser coupled cavity ring-down spectrometer. We have experimentally achieved the ortho-to-para ratio (OPR) of (1.03 ± 0.24) and (1.08 ± 0.14) at room temperature (296 K) for the allowed and forbidden transitions of NH3, respectively. Furthermore, our experimental findings confirm that the nuclear spin-symmetry is conserved under the nonreactive perturber-induced collisional processes. This study paves the way to directly probe the nuclear spin-isomers of gas-phase NH3 and thus may lead to an in-depth understanding of nuclear spin-isomerism associated with various physical and chemical processes. This work shows the high-resolution probing of ortho- and para-nuclear spin-isomers of NH3 in the gas phase at room temperature using quantum cascade laser coupled cavity ring-down spectroscopy at 6.2 µm mid-IR spectral region. [ABSTRACT FROM AUTHOR]

In situ measurements of water vapour isotopic composition in polar regions has provided needed constrains of post-deposition processes involved in the archiving of the climatic signal in ice core records. During polar winter, the temperatures, and thus the specific humidity, are so low that current commercial techniques are not able to measure the vapour isotopic composition with enough precision. Here, we make use of new developments in infrared spectroscopy and combine an optical-feedback frequency-stabilised laser source (OFFS technique) using a V-shaped cavity optical feedback (VCOF) cavity and a high-finesse cavity ring-down spectroscopy (CRDS) cavity to increase the signal-to-noise ratio while measuring absorption transitions of water isotopes. We present a laboratory infrared spectrometer leveraging all these techniques dedicated to measure water vapour isotopic composition at low humidity levels. At 400 ppmv , the instrument demonstrates a precision of 0.01 ‰ and 0.1 ‰ in δ18O and d-excess, respectively, for an integration time of 2 min. This set-up yields an isotopic composition precision below 1 ‰ at water mixing ratios down to 4 ppmv , which suggests an extrapolated precision in δ18O of 1.5 ‰ at 1 ppmv. Indeed, thanks to the stabilisation of the laser by the VCOF, the instrument exhibits extremely low drift and very high signal-to-noise ratio. The instrument is not hindered by a strong isotope–humidity response which at low humidity can create extensive biases on commercial instruments. [ABSTRACT FROM AUTHOR]

Context. The hydrogen deuteride (HD) molecule is an important deuterium tracer in astrophysical studies. The atmospheres of gas giants are dominated by molecular hydrogen, and the simultaneous observation of H2 and HD lines provides reliable information on the D/H ratios on these planets. The reference spectroscopic parameters play a crucial role in such studies. Under the thermodynamic conditions encountered in these atmospheres, spectroscopic studies of HD require not only the knowledge of line intensities and positions but also accurate reference data on pressure-induced line shapes and shifts. Aims. Our aim is to provide accurate collision-induced line-shape parameters for HD lines that cover any thermodynamic conditions relevant to the atmospheres of giant planets, namely any relevant temperature, pressure, and perturbing gas composition (the H2–He mixture). Methods. We performed quantum-scattering calculations on our new, highly accurate ab initio potential energy surface (PES), and we used scattering S matrices obtained in this way to determine the collision-induced line-shape parameters. We used cavity ring-down spectroscopy to validate our theoretical methodology. Results. We report accurate collision-induced line-shape parameters for the pure rotational R(0), R(1), and R(2) lines, the most relevant HD lines for investigations of the atmospheres of the giant planets. Besides the basic Voigt-profile collisional parameters (i.e., the broadening and shift parameters), we also report their speed dependences and the complex Dicke parameter, which can influence the effective width and height of the HD lines up to almost a factor of 2 for giant planet conditions. The sub-percent-level accuracy reached in this work is a considerable improvement over previously available data. All the reported parameters (and their temperature dependences) are consistent with the HITRAN database format, hence allowing for the use of the HITRAN Application Programming Interface (HAPI) for generating the beyond-Voigt spectra of HD. [ABSTRACT FROM AUTHOR]

Accurate measurement of water vapor isotopes (δ18O and δ2H) is fundamental for advancing our understanding of the hydrological cycle and improving hydrological model accuracy. This study introduces an innovative calibration methodology using a controlled evaporation mixer (CEM) for determining stable isotopic ratios in atmospheric water vapor via cavity ring-down spectroscopy. The CEM technique reliably produces a stable water vapor stream, crucial for enhancing the precision and accuracy of isotopic measurements. Its rapid adaptation to changes in water vapor concentration and compatibility with different water standards enhance calibration reliability. Demonstrated reproducibility in generating water vapor across a broad concentration range from 900 to over 25,000 ppmv, coupled with a substantial reduction in memory effects, makes this approach highly effective in both laboratory and field settings. This calibration advancement greatly enhances research capabilities for continuous atmospheric water vapor analysis, providing deeper insights into hydrological processes and atmospheric dynamics. [ABSTRACT FROM AUTHOR]

A cavity ring-down spectroscopy (CRDS) system based on the time-division multiplexing (TDM) and an improved Whittaker-Henderson (W-H) filtering algorithm was proposed to synchronous detect of methane (CH4) and carbon dioxide (CO2) gas absorption spectroscopy. The mechanical optical switch was used to quickly switch distributed feedback (DFB) lasers with different wavelengths in the optical path.And the adaptive W-H filtering algorithm combined with convolutional neural network (CNN) could quickly and accurately obtain the best weight parameters to achieve effective denoising of absorption spectrum.In addition, the gradient concentration of CH4 and CO2weredetected and the limit of detection (LOD) of CRDS system was studied.The results of experiment demonstrated that the system could detect CO2 and CH4 in real time and had good stability. Allan deviation analysis shows that the LOD of CH4 and CO2 are 8 ppb and 0.85 ppm under the average number of 1. The LOD of CH4 and CO2 can be optimized to 2 ppb and 0.16 ppm under the optimal average number. In short, the proposed system had high sensitivity, good stability and could measure various gases synchronously, which had important application potential in the field of gas monitoring. [ABSTRACT FROM AUTHOR]

The application of stable isotope analysis (SIA) to the fields of ecology and animal biology has rapidly expanded over the past three decades, particularly with regards to water analysis. SIA now provides the opportunity to monitor migration patterns, examine food webs, and assess habitat changes in current and past study systems. While carbon and nitrogen SIA of biological samples have become common, analyses of oxygen or hydrogen are used more sparingly despite their promising utility for tracing water sources and animal metabolism. Common ecological applications of oxygen or hydrogen SIA require injecting enriched isotope tracers. As such, methods for processing and analyzing biological samples are tailored for enriched tracer techniques, which require lower precision than other techniques given the large signal-to-noise ratio of the data. However, instrumentation advancements are creating new opportunities to expand the applications of high-throughput oxygen and hydrogen SIA. To support these applications, we update methods to distill and measure water derived from biological samples with consistent precision equal to, or better than, ± 0.1 ‰ for δ17O, ± 0.3 ‰ for δ18O, ± 1 ‰ for δ2H, ± 2 ‰ for d-excess, and ± 15 per meg for Δ17O. [ABSTRACT FROM AUTHOR]

Rationale: Water-stable isotopes in rainfall are powerful tracers of atmospheric processes at different spatial and temporal scales. However, commercially available rain samplers for isotopic analysis are prohibitively expensive, especially for high spatial resolution networks and studies conducted in developing countries. A lowcost, simple, and robust sampler was designed for event and monthly rainfall samplings. Methods: Rainfall collectors were built based on existing designs provided in the literature and using easily accessible materials. Event samplers were filled with different volumes of reference water and left for 72 h in laboratory conditions to determine the minimum amount of rainfall to be collected to minimize isotopic fractionation, from both postsampling evaporation and equilibration. Samples were analyzed using dual-inlet isotope ratio mass spectrometry and cavity ring-down spectroscopy. Results: For samples larger than 4% of the bottle's capacity, the evaporative enrichment due to Rayleigh distillation is negligible compared to the overall analytical uncertainty. Using a tube connecting the funnel to the water sample has proved to reduce postsampling evaporation by at least five times. To limit water self-diffusion, we recommend collecting the largest rainfall amount possible. Under these conditions, these collectors are suitable for rainfall sampling for isotopic analysis. Conclusions: This low-cost methodology will enable isotopic sampling of precipitation at high spatial resolutions and democratize the use of isotopes for hydrological studies in developing countries. All instructions for building and using these samplers are made openly accessible to the scientific community so they can be repeated and adapted to the needs of each project. [ABSTRACT FROM AUTHOR]

Current formaldehyde (HCHO) measurement networks rely on the TO-11A offline chemical derivatization technique, which can be resource intensive and limited in temporal resolution. In this work, we evaluate the field performance of three new commercial instruments for continuous in situ formaldehyde monitoring: the Picarro cavity ring-down spectroscopy G2307 gas concentration analyzer and Aeris Technologies' mid-infrared absorption Pico and Ultra gas analyzers. All instruments require regular drift correction, which is accomplished through instrument zeroing using dinitrophenylhydrazine (DNPH)-coated cartridges, Drierite, or molecular sieves, while heated Hopcalite failed to remove all incoming HCHO. We show that a modified precision estimate accounting for regular instrument zeroing results in values of 0.09, 0.20, and 0.22 ppb at a 20 min integration time for the G2307, Ultra, and Pico, respectively. After applying standard addition and dynamic dilution calibrations, all instruments agreed within 13 % and were well correlated with each other (all r ≥ 0.90). TO-11A HCHO observations resulted in a normalized mean bias of -58 % compared to co-located Picarro G2307 measurements (r=0.62 , slope = 0.38, int = 0.07 ppb HCHO). Using a 6-month deployment period in the Atlanta metropolitan area, we determined that the Picarro G2307 and Aeris units have sufficient accuracy and precision to capture the Atlanta spatial HCHO gradient. We find that midday HCHO concentrations have decreased by 22.3 % since 1999 in the city's urban core, and DNPH measurements at a nearby Photochemical Assessment Monitoring Station (PAMS) site show a greater decrease of 53 %. [ABSTRACT FROM AUTHOR]

Water stable isotopologue analysis is widely used to disentangle ecohydrological processes. Yet, there are increasing reports of measurement uncertainties for established and emerging methods, such as cryogenic vacuum extraction (CVE) or cavity ring‐down spectroscopy (CRDS). With this study, we investigate two pitfalls, that potentially contribute to uncertainties in water‐stable isotopologue research. To investigate fractionation sources in CVE, we extracted pure water of known isotopic composition with cotton, glass wool or without cover and compared the isotopologue results with non‐extracted reference samples. To characterise the dependency of δ2H and δ18O on the water mixing ratio in CRDS, which is of high importance for in‐situ applications with large natural variations in mixing ratios, we chose samples with a large range of isotopic compositions and determined δ2H and δ18O for different water mixing ratios with two CRDS analysers (Picarro, Inc.). Cotton wool had a strong fractionation effect on δ2H values, which increased with more 2H‐enriched samples. δ2H and δ18O values showed a strong dependency on the water mixing ratio analysed with CRDS with differences of up to 34.5‰ (δ2H) and 3.9‰ (δ18O) for the same sample at different mixing ratios. CVE and CRDS, now routinely applied in water stable isotopologue research, come with pitfalls, namely fractionation effects of cover materials and water mixing ratio dependencies of δ2H and δ18O, which can lead to erroneous isotopologue results and thus, invalid conclusions about (ecohydrological) processes. These practical issues identified here should be reported and addressed adequately in water‐stable isotopologue research. [ABSTRACT FROM AUTHOR]

Mitigation of greenhouse gases requires a precise knowledge of their sources at both global and regional scales. With improving measurement techniques, in situ δ(13C,CH4) records are analysed in a growing number of studies to characterise methane emissions and to evaluate inventories at regional and local scales. However, most of these studies cover short time periods of a few months, and the results show a large regional variability. In this study, a 6-year time record of in situ δ(13C,CH4) , measured with a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany, is analysed to obtain information about seasonal variations and trends of CH 4 emissions. The Keeling plot method is applied to atmospheric measurements on different timescales, and the resulting source contributions are used to evaluate the CH 4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGAR v6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW). The mean isotopic carbon source signature for the Heidelberg catchment area derived from atmospheric measurements is (-52.3±0.4) ‰ and shows an annual cycle with 5.8 ‰ more depleted values in summer than in winter. This annual cycle can only be partly explained by seasonal variations in the 13 C-enriched emissions from heating and reveals strong seasonal variations in biogenic CH 4 emissions in the Heidelberg catchment area, which are not included in EDGAR v6.0. The comparison with emission inventories also shows that EDGAR v6.0 overestimates the CH 4 emissions from less depleted sources. In situ CH 4 isotope analysers at continental and urban monitoring stations can make an important contribution to the verification and improvement of emission inventories. [ABSTRACT FROM AUTHOR]

Rationale: The presence of substantial amounts of dissolved salts creates serious difficulties in isotope analyses of water samples using conventional isotope ratio mass spectrometry. Although nowadays laser‐based instruments are increasingly used for this purpose, a comprehensive assessment of isotope effects associated with direct analyses of aqueous saline solutions using this technology is lacking. Methods: Here we report the results of laboratory experiments aimed at quantifying isotope effects associated with direct, δ2H, δ18O and δ17O analyses of single‐salt solutions and double‐salt mixtures prepared with a water of known isotopic composition. Three single‐salt solutions (NaCl, CaCl2 and MgSO4) and two double‐salt mixtures (NaCl + CaCl2 and NaCl + MgSO4) were prepared and investigated for a wide range of molalities. The triple‐isotope composition of the prepared solutions was analysed with the aid of a Picarro L2140‐i Cavity Ring‐Down Spectroscopy analyser. Results: The NaCl and CaCl2 solutions revealed small negative salt effects, independent of molality and comparable with measurement uncertainty. The MgCl2 solution showed the highest salt effects, reaching saturated solution ca. +2.7‰ (2H), −3.5‰ (18O) and −1.7‰ (17O). Salt effects for the double‐salt mixtures generally mirrored the effects observed for the single‐salt solutions. The observed salt effects are discussed in the context of processes occurring during the injection of the salt solutions into the vaporizer unit of the CRDS analyser. Conclusions: The presented study has demonstrated feasibility of direct, triple‐isotope analyses of aqueous salt solutions using a Picarro L2140‐i CRDS analyser for a broad range of salinities up to saturated conditions. Large uncertainties of 17O‐excess determinations for solutions forming hydrated salts preclude the use of this parameter for interpretation purposes. [ABSTRACT FROM AUTHOR]

We present a high-resolution study on the B2Π-X2Π electronic origin band spectrum of the C6H radical with its center at ~18990 cm-1 The C6H radicals are produced in a pulsed supersonic slit-jet discharge source and detected in direct absorption by sensitive cavity ring-down spectroscopy. By using a home-made narrow linewidth nanosecond pulsed laser source, the experimental spectrum allows to resolve the ∧-type doublet fine structures in high-J rotational lines. A set of improved B2Π state constants, including the ∧-type doubling parameters of p′ = −1.16(9)x10−3 cm−1q′ = -1.22(7)x10−4 cm−1 are determined from analysis of the experimental spectrum. An analysis on the spectral line profile has resulted in a significant linewidth broadening of ~0.05±0.01 cm−1, corresponding to a B2Π state lifetime of ~100±20 ps. The short lifetime of the excited B2Π state is proposed due to fast internal vibronic couplings to high-lying vibronic levels of lower electronic states. [ABSTRACT FROM AUTHOR]

We present the saturated absorption spectroscopy of the 30012←00001 band of 12C16O2 by a comb-locked cavity ring-down spectrometer near 1.57 µm. Positions of 37 lines with rotational quantum numbers up to 68 were determined with an accuracy of a few kHz. Comparisons of the ro-vibrational energy levels determined in this work with the Doppler-limited experimental values from literature and those from the CDSD2019 databank are given. Deviations exceeding 1 MHz were observed in the transitions blended by other carbon dioxide isotopologues. [ABSTRACT FROM AUTHOR]

Rationale: Soil microbial heterotrophic C‐CO2 respiration is important for C cycling. Soil CO2 differentiation and quantification are vital for understanding soil C cycling and CO2 emission mitigation. Presently, soil microbial respiration (SR) quantification models are based on native soil organic matter (SOM) and require consistent monitoring of δ13C and CO2. Methods: We present a new apparatus for achieving in situ soil static chamber incubation and simultaneous CO2 and δ13C monitoring by cavity ring‐down spectroscopy (CRDS) coupled with a soil culture and gas introduction module (SCGIM) with multi‐channel. After a meticulous five‐point inter‐calibration, the repeatability of CO2 and δ13C values by using CRDS‐SCGIM were determined, and compared with those obtained using gas chromatography (GC) and isotope ratio mass spectrometry (IRMS), respectively. We examined the method regarding quantifying SR with various concentrations and enrichment of glucose and then applied it to investigate the responses of SR to the addition of different exogenous organic materials (glucose and rice residues) into paddy soils during a 21‐day incubation. Results: The CRDS‐SCGIM CO2 and δ13C measurements were conducted with high precision (< 1.0 µmol/mol and 1‰, respectively). The optimal sampling interval and the amount added were not exceeded 4 h and 200 mg C/100 g dry soil in a 1 L incubation bottle, respectively; the 13C‐enrichment of 3%–7% was appropriate. The total SR rates observed were 0.6–4.2 µL/h/g and the exogenous organic materials induced ‐49%–28% of priming effects in native SOM mineralisation. Conclusions: Our results show that CRDS‐SCGIM is a method suitable for the quantification of soil microbial CO2 respiration, requiring less extensive lab resources than GC/IRMS. [ABSTRACT FROM AUTHOR]

To effectively monitor the highly heterogeneous urban CO2 emissions using atmospheric observations, there is a need to deploy cost-effective CO2 sensors at multiple locations within the city with sufficient accuracy to capture the concentration gradients in urban environments. Its measurements could be used as input of an atmospheric inversion system for the quantification of emissions at the sub-city scale or separate specific sectors. Such quantification would offer valuable insights into the efficacy of local initiatives and could also identify unknown emission hotspots that require attention. Here we present the development and evaluation of a mid-cost CO2 instrument designed for continuous monitoring of atmospheric CO2 concentrations with a target accuracy of 1 ppm on hourly mean measurement. We assess the sensor sensitivity in relation to environmental factors such as humidity, pressure, temperature and CO2 signal, which leads to the development of an effective calibration algorithm. Since July 2020, eight mid-cost instruments have been installed within the city of Paris and its vicinity to provide continuous CO2 measurements, complementing the seven high-precision Cavity Ring-Down Spectroscopy (CRDS) stations that have been in operation since 2016. A data processing system, called CO2 calqual, has been implemented to automatically handle data quality control, calibration and storage, which enables the management of extensive real-time CO2 measurements from the monitoring network. Colocation assessments with the high-precision instrument show that the accuracies of the eight mid-cost instruments are within the range of 1.0 to 2.4 ppm for hourly afternoon (12–17 UTC) measurements. The long-term stability issues require manual data checks and instrument maintenance. The analyses show that CO2 measurements can provide evidence for underestimations of CO2 emissions in the Paris region and a lack of several emission point sources in the emission inventory. Our study demonstrates promising prospects in integrating mid-cost measurements along with high precision data into the subsequent atmospheric inverse modeling to improve the accuracy of quantifying the fine-scale CO2 emissions in the Paris metropolitan area. [ABSTRACT FROM AUTHOR]

To effectively monitor the highly heterogeneous urban CO2 emissions using atmospheric observations, there is a need to deploy cost-effective CO2 sensors at multiple locations within the city with sufficient accuracy to capture the concentration gradients in urban environments. Its measurements could be used as input of an atmospheric inversion system for the quantification of emissions at the sub-city scale or separate specific sectors. Such quantification would offer valuable insights into the efficacy of local initiatives and could also identify unknown emission hotspots that require attention. Here we present the development and evaluation of a mid-cost CO2 instrument designed for continuous monitoring of atmospheric CO2 concentrations with a target accuracy of 1 ppm on hourly mean measurement. We assess the sensor sensitivity in relation to environmental factors such as humidity, pressure, temperature and CO2 signal, which leads to the development of an effective calibration algorithm. Since July 2020, eight mid-cost instruments have been installed within the city of Paris and its vicinity to provide continuous CO2 measurements, complementing the seven high-precision Cavity Ring-Down Spectroscopy (CRDS) stations that have been in operation since 2016. A data processing system, called CO2calqual, has been implemented to automatically handle data quality control, calibration and storage, which enables the management of extensive real-time CO2 measurements from the monitoring network. Colocation assessments with the high-precision instrument show that the accuracies of the eight mid-cost instruments are within the range of 1.0 to 2.4 ppm for hourly afternoon (12–17 UTC) measurements. The long-term stability issues require manual data checks and instrument maintenance. The analyses show that CO2 measurements can provide evidence for underestimations of CO2 emissions in the Paris region and a lack of several emission point sources in the emission inventory. Our study demonstrates promising prospects in integrating mid-cost measurements along with high precision data into the subsequent atmospheric inverse modeling to improve the accuracy of quantifying the fine-scale CO2 emissions in the Paris metropolitan area. [ABSTRACT FROM AUTHOR]

We have applied cavity ring-down spectroscopy (CRDS) to the study of the 166Er isotope in an atomic beam. These measurements were realized with an external cavity diode laser tuned to the 400.9 nm atomic transition of erbium and a customized high-finesse ring-down optical cavity under vacuum. Erbium atomic beams of different number densities were generated in a tantalum foil micro-crucible within the cavity. Absorbance values of the 166Er isotope between 3 × 10−6 and 7 × 10−5 were measured with a best-case precision on the order of 10−6, which is remarkable when considering the extreme temperatures at which the measurements were conducted, and the short detection path which is characteristic of collimated atomic beams. Number densities of erbium atoms were inferred to be between 2 × 106 and 6 × 107 cm−3. This work demonstrates for the first time the ability of studying dilute atomic beams of refractory materials with high accuracy utilizing CRDS. In these initial studies, we used erbium as a model system, but we expect to extend the proposed approach to the measurement of isotopes of uranium and plutonium for nuclear non-proliferation applications. [ABSTRACT FROM AUTHOR]

The article presents a dual‐optimized adaptive algorithm based on continuous wavelet transform and derivative precise peak capture is developed for fiber cavity ring‐down spectroscopy. Adaptive spectral signal processing is achieved so that peak selection blindness can be effectively solved. To verify the performance of the dual‐optimized adaptive algorithm, a highly sensitive refractive index sensor using a bandgap fiber‐based linear fiber cavity is demonstrated. The developed dual‐optimized adaptive algorithm is compared with the conventional maximum extraction algorithm, and the results show that the dual‐optimized adaptive algorithm has a better performance in suppressing noise and processing superimposed peaks. A stable enhancement factor of 5 is obtained, indicating that the newly developed dual‐optimized adaptive algorithm can generate a high‐quality cavity ring‐down spectrum for applications including refractive index sensors, biosensors, strain gauges, and pressure sensors. [ABSTRACT FROM AUTHOR]

δ (13CH4) and the mole fraction of CH4 have been measured continuously since April 2014 using a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany. This 6-year time series shows an increasing trend of (6.8±0.3) nmol mol-1 a -1 for the CH4 mole fraction between 2014 and 2020. δ (13CH4) decreases by (-0.028±0.002) ‰ a-1 over this time period. In this study, seasonal variations and trends of CH4 emissions in the catchment area of Heidelberg are analysed using three approaches by applying the Miller-Tans method to atmospheric measurements on different time scales. The mean δ 13C isotopic source signature for the Heidelberg catchment area is (-52.5±0.3) ‰ (moving Miller-Tans approach). In all three approaches, there is no significant trend in the monthly mean source signature over the last six years. However, more depleted source signature values occur in summer. This annual cycle in 13C-CH4 sources, with a peak-to-peak amplitude of -6.2 ‰ can only be partially explained by seasonal variations in CH4 emissions from heating. Additional seasonal variations probably occur in biogenic CH4 emissions from waste water, landfills or dairy cows. Furthermore, the source contributions derived from atmospheric measurements are used to evaluate the CH4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGARv6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW – Landesanstalt für Umwelt Baden-Württemberg). The mean δ (13CH4) source signature determined from the LUBW inventory agrees well with the result from atmospheric measurements. However, the signature determined from EDGARv6.0 data is less depleted by about 7 ‰. Thus, EDGARv6.0 seems to overestimate CH4 emissions from more enriched sources. [ABSTRACT FROM AUTHOR]

Rationale: The accuracy determined in the routine analysis of water isotopes (δ17O, δ18O, δ2H) using cavity ring‐down spectroscopy is greatly affected by the memory effect (ME), a sample‐to‐sample carryover that biases measurements. This study aims to develop a simple method that rapidly removes the ME. Methods: We developed a method, designed for the Picarro L2140‐i, that removes the ME by injecting small amounts of water with an extreme isotopic value ("kick") in the opposite direction of the ME. We conducted 11 experiments to identify the optimal kick for pairs of isotopically enriched and depleted samples. Once quantified, the optimal kick was used to create an ME‐free, unbiased calibration curve, which was verified using international and internal lab standards. Results: Our kick method removes the ME very efficiently in half the time it takes for experiments without a kick. The optimal number of kick injections required to minimize stabilization time between standards of different compositions is three injections of δ2H ≈ −1000‰ water per a 100‰ difference between standards. Three runs of routine measurements using the kick method resulted in uncertainties of 0.03‰, 0.2‰, and 5 permeg for δ18O, δ2H, and 17O‐excess, respectively. Conclusions: This study demonstrates a new method for rapidly removing the ME. Our kick protocol is a readily available, cheap, and efficient approach to reduce instrumental bias and improve measurement accuracy. [ABSTRACT FROM AUTHOR]

The carbon isotope composition of respired CO2 (δ13CR) and bulk organic matter (δ13CB) of various plant compartments informs about the isotopic fractionation and substrate of respiratory processes, which are crucial to advance the understanding of carbon allocation in plants. Nevertheless, the variation across organs, species and seasons remains poorly understood. Cavity Ring-Down Laser Spectroscopy was applied to measure δ13CR in leafy shoots and woody stems of maple (Acer platanoides L.), oak (Quercus robur L.) and cedar (Thuja occidentalis L.) trees during spring and late summer. Photosynthesis, respiration, growth and non-structural carbohydrates were measured in parallel to evaluate potential drivers for respiratory fractionation. The CO2 respired by maple and oak shoots was 13C-enriched relative to δ13CB during spring, but not late summer or in the stem. In cedar, δ13CR did not vary significantly throughout organs and seasons, with respired CO2 being 13C-depleted relative to δ13CB. Shoot δ13CR was positively related to leaf starch concentration in maple, while stem δ13CR was inversely related to stem growth. These relations were not significant for oak or cedar. The variability in δ13CR suggests (i) different contributions of respiratory pathways between organs and (ii) seasonality in the respiratory substrate and constitutive compounds for wood formation in deciduous species, less apparent in evergreen cedar, whose respiratory metabolism might be less variable. [ABSTRACT FROM AUTHOR]

The editorial in "Frontiers in Physics" discusses recent advancements in cavity-enhanced optical spectroscopy, highlighting improvements in precision, sensitivity, and applications in various fields such as environmental monitoring, quantum electrodynamics, and biomedical research. Different studies featured in the research topic showcase innovative methodologies and theoretical insights in cavity ring-down spectroscopy, optical frequency comb techniques, and the use of cavities for precise comb characterization and absorption measurements. These developments are crucial for enhancing environmental monitoring, medical diagnostics, and understanding molecular dynamics. [Extracted from the article]

With an atmospheric concentration of approximately 2000 parts per billion (ppbV, 10 -9), methane (CH 4) is the second most abundant greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO 2). The task of long-term and spatially resolved GHG monitoring to verify whether climate policy actions are effective is becoming more crucial as climate change progresses. In this paper we report the CH 4 concentration readings of our photoacoustic (PA) sensor over a 5 d period at Hohenpeißenberg, Germany. As a reference device, a calibrated cavity ring-down spectrometer, Picarro G2301, from the meteorological observatory of the German Weather Service (DWD) was employed. Trace gas measurements with photoacoustic instruments promise to provide low detection limits at comparably low costs. However, PA devices are often susceptible to cross-sensitivities related to fluctuating environmental conditions, e.g. ambient humidity. The obtained results show that for PA sensor systems non-radiative relaxation effects induced by varying humidity are a non-negligible factor. Applying algorithm compensation techniques, which are capable of calculating the influence of non-radiative relaxation effects on the photoacoustic signal, increase the accuracy of the photoacoustic sensor significantly. With an average relative deviation of 1.11 % from the G2301, the photoacoustic sensor shows good agreement with the reference instrument. [ABSTRACT FROM AUTHOR]

The electronic transition spectra of the indene molecular cation (In + , C 9 H 8 + ) in the 550–580 nm region has been measured in the gas phase in direct absorption. The spectra were experimentally recorded using sensitive cavity ring-down spectroscopy in a supersonically expanding planar plasma. Two lifetime-broadened vibronic bands are assigned to the 2 A ′ ′ - X 2 A ′ ′ electronic transition system of In + . A set of indicative spectroscopic parameters have been obtained from a band contour analysis of the 0 0 0 band in combination with supporting ab-initio calculations. The inferred Lorentz line width of 4.0 ± 0.5 cm − 1 indicates an upper state lifetime of 1.2 ± 0.1 ps . The laboratory data are compared to the diffuse interstellar bands (DIBs), and no matches can be found. Upper limits for In + column densities in the diffuse interstellar medium have also been estimated from six sightline spectra. [ABSTRACT FROM AUTHOR]

The electronic transition spectra of the indene molecular cation (In + , C 9 H 8 + ) in the 550–580 nm region has been measured in the gas phase in direct absorption. The spectra were experimentally recorded using sensitive cavity ring-down spectroscopy in a supersonically expanding planar plasma. Two lifetime-broadened vibronic bands are assigned to the 2 A ′ ′ - X 2 A ′ ′ electronic transition system of In + . A set of indicative spectroscopic parameters have been obtained from a band contour analysis of the 0 0 0 band in combination with supporting ab-initio calculations. The inferred Lorentz line width of 4.0 ± 0.5 cm − 1 indicates an upper state lifetime of 1.2 ± 0.1 ps . The laboratory data are compared to the diffuse interstellar bands (DIBs), and no matches can be found. Upper limits for In + column densities in the diffuse interstellar medium have also been estimated from six sightline spectra. [ABSTRACT FROM AUTHOR]

We monitored stable water isotopes in liquid precipitation and atmospheric water vapour (δv) using in situ cavity ring‐down spectroscopy (CRDS) over a 2 month period in an urban green space area in Berlin, Germany. Our aim was to better understand the origins of atmospheric moisture and its link to water partitioning under contrasting urban vegetation. δv was monitored at multiple heights (0.15, 2 and 10 m) in grassland and forest plots. The isotopic composition of δv above both land uses was highly dynamic and positively correlated with that of rainfall indicating the changing sources of atmospheric moisture. Further, the isotopic composition of δv was similar across most heights of the 10 m profiles and between the two plots indicating high aerodynamic mixing. Only at the surface at ~0.15 m height above the grassland δv showed significant differences, with more enrichment in heavy isotopes indicative of evaporative fractionation especially after rainfall events. Further, disequilibrium between δv and precipitation composition was evident during and right after rainfall events with more positive values (i.e., values of vapour higher than precipitation) in summer and negative values in winter, which probably results from higher evapotranspiration and more convective precipitation events in summer. Our work showed that it is technically feasible to produce continuous, longer‐term data on δv isotope composition in urban areas from in situ monitoring using CRDS, providing new insights into water cycling and partitioning across the critical zone of an urban green space in Central Europe. Such data have the potential to better constrain the isotopic interface between the atmosphere and the land surface and to thus, improve ecohydrological models that can resolve evapotranspiration fluxes. [ABSTRACT FROM AUTHOR]

Dark CO 2 fixation by bacteria is believed to be particularly important in oligotrophic ecosystems. However, only a few studies have characterized the role of bacterial dissolved inorganic carbon (DIC) fixation in global carbon dynamics. Therefore, this study quantified the primary production (PP), total bacteria dark CO 2 fixation (TB DIC fixation), and heterotrophic bacterial production (HBP) in the warm and oligotrophic Red Sea using stable-isotope labeling and cavity ring-down spectroscopy (13 C–CRDS). Additionally, we assessed the contribution of bacterial DIC fixation (TB DIC %) relative to the total DIC fixation (total DIC fixation). Our study demonstrated that TB DIC fixation increased the total DIC fixation from 2.03 to 60.45 µ g C L -1 d -1 within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 ± 0.02 % of the photic layer total DIC fixation. The highest TB DIC fixation values were measured at the surface and deep (400 m) water with an average value of 5.23 ± 0.45 and 4.95 ± 1.33 µ g C L -1 d -1 , respectively. These findings suggest that the non-photosynthetic processes such as anaplerotic DIC reactions and chemoautotrophic CO 2 fixation extended to the entire oxygenated water column. On the other hand, the percent of TB DIC contribution to total DIC fixation increased as primary production decreased (R2=0.45 , p<0.0001), suggesting the relevance of increased dark DIC fixation when photosynthetic production was low or absent, as observed in other systems. Therefore, when estimating the total carbon dioxide production in the ocean, dark DIC fixation must also be accounted for as a crucial component of the carbon dioxide flux in addition to photosynthesis. [ABSTRACT FROM AUTHOR]

Rovibrationally resolved spectra of the Nj=22, Ka=0←1 transition and of the Nj=23, Ka=0←0 and Ka=1←0 transitions of the hydrogen‐bonded (HF)2 have been measured in the near infrared range near 1.3 μm by cw‐diode laser cavity ring‐down spectroscopy in a pulsed supersonic slit jet expansion. The spectroscopic assignment and analysis provided an insight into the dynamics of these highly‐excited vibrational states, in particular concerning the predissociation of the hydrogen bond and the tunneling process of the hydrogen bond switching. Together with our previously analyzed spectra of the Nj=21 and Nj=22 components, the mode‐specific dynamics in all three components of this triad can now be compared. In the N=2 triad, the HF‐stretching vibration is excited by two quanta with similar excitation energy, but the quanta are distributed in three different ways, which has a distinct influence on the dynamics. The observed band centers and tunneling splittings are in agreement with our recent calculations on the (HF)2 potential energy hypersurface SO‐3, resolving the long‐standing discussion about the symmetry ordering of polyad levels in this overtone region. The results are also discussed in relation to the general questions of non‐statistical reaction dynamics of polyatomic molecules and clusters and in relation to quasi‐adiabatic channel above barrier tunneling. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a key nutrient required by all living organisms for growth and development, but is a limiting resource for many organisms. Organisms that feed on material with low N content, such as wood, might be particularly prone to N limitation. In this study, we investigated the degree to which the xylophagous larvae of the stag beetle Ceruchus piceus (Weber) use associations with N-fixing bacteria to acquire N. We paired acetylene reduction assays by cavity ring-down absorption spectroscopy (ARACAS) with 15N2 incubations to characterize rates of N fixation within C. piceus. Not only did we detect significant N fixation activity within C. piceus larvae, but we calculated a rate that was substantially higher than most previous reports for N fixation in insects. While taking these measurements, we discovered that N fixation within C. piceus can decline rapidly in a lab setting. Consequently, our results demonstrate that previous studies, which commonly keep insects in the lab for long periods of time prior to and during measurement, may have systematically under-reported rates of N fixation in insects. This suggests that within-insect N fixation may contribute more to insect nutrition and ecosystem-scale N budgets than previously thought. [ABSTRACT FROM AUTHOR]

Knowledge of impurities in matrix gas is one of the critical requirements for the preparation of class I type calibration gas mixtures (primary reference gas mixtures, PRGMs) as per ISO 6142‐1. PRGMs are prepared gravimetrically using high‐purity component gas and high‐grade nitrogen, here 99.9995 % (5.5 N) as matrix gas. In this study, quantification of gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5 N nitrogen is performed using CRDS (cavity ring down spectroscopy). Carbon dioxide (CO2) and total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC‐FID), while the determination of nitrogen dioxide (NO2) impurity is conducted colorimetrically using a UV‐Vis spectrophotometer. Total impurities in 5.5 N nitrogen are found to be (2945±21.5) ppb. The impact of utilizing this nitrogen is examined through the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5 N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO. However, the component gas impurity present in nitrogen potentially affect the accuracy of gravimetrically prepared gas mixture. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cavity ring-down spectroscopy (CRDS) has been applied to retrieve accurate Rayleigh scattering cross-sections, σ Rayl. for a set of atmospheric gases at ~ 408 nm. Step pressure changes and pressure ramps were used in three different but similar optical cavities to measure light extinction by N2, O2, Ar, CO, CO2, N2O, CH4 and synthetic air (SA). The experimentally determined σ Rayl. were compared with σ Rayl. values calculated for these atmospheric gases using knowledge of extrapolated literature values of the refractive index (n) and King correction factors measured in different spectral regions. The difference between measured and calculated σ Rayl. using the most recently published dispersion relationship for N2O and CH4 is ~ 0.6%. This confirms the improved accuracy of the new dispersion relationship. The calculated and measured σ Rayl. agreed on average within 0.6%, 2.4%, 1.2%, 2.2%, and 1.5% for the gases CO2, N2 O2, SA, and Ar at ~ 408 nm. However, for CO, the difference is 4.1%, i.e. more than twice the error. This implies that improved knowledge of the dispersion relationship for CO, and thus the refractive index and King correction factors, would be of value to calculate σ Rayl. in the blue spectral region. [ABSTRACT FROM AUTHOR]

The complex distribution of particle charge states resulting from neutralization processes by radioactive or soft X-ray charge neutralizers is a well-documented problem in aerosol science. Here, we demonstrate that non-idealities in the collection efficiency of an impactor allows for the transmission of an unexpected population of multiply charged particles by a differential mobility analyzer that can bias optical measurements. The extinction cross sections (Cext) of ammonium sulfate particles were quantified using cavity ring-down spectroscopy and particle counting. Particles were selected by electrical mobility (i.e., a metric of particle size) using a differential mobility analyzer (DMA) or electrical mobility and mass selected by a tandem DMA and aerosol particle mass analyzer (APM), respectively, to elucidate multiple charging artifacts. Measured Cext exhibited statistically significant differences at particle sizes near the impactor cut point implying that these multiply charged particles should not be present and could not be confirmed by parallel size distribution measurements. Additionally, comparison of Cext with Mie theory demonstrates that misclassification of the multiply charged particles can give rise to numerically accurate results. To understand these observations, the collection efficiency (CE) of four impactors from similar electrostatic classifiers was investigated. From these measurements, it was determined that the nominal and actual diameters of the impactors differed by −0.5% (457 μm vs. (455 ± 1) μm, respectively (uncertainty is 1σ standard deviation)) but the average Stk50 (the Stokes number at the cut-point, D50) values differed by ≈ 23% (0.23 vs. 0.18 ± 0.01, respectively). The measured CE as a function of √Stk (a metric of particle aerodynamic size) exhibits a long tail toward higher √Stk values, allowing for transmission of the larger and multiply charged particles observed in the optical measurements. These measurements highlight the utility of using orthogonal, spectroscopic methods to quantify the presence of multiply charged particles. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Plants can serve as sensitive bioindicators of the presence of contaminant vapors in the atmosphere. This work describes a novel laboratory-based gas exposure system capable of calibrating plants as bioindicators for the detection and delineation of the atmospheric contaminant hydrogen fluoride (HF) as a preparatory step for monitoring release emissions. To evaluate changes in plant phenotype and stress-induced physiological effects attributed to HF alone, the gas exposure chamber must have additional controls to simulate otherwise optimal plant growth conditions including variables such as light intensity, photoperiod, temperature, and irrigation. The exposure system was designed to maintain constant growth conditions during a series of independent experiments that varied between optimal (control) and stressful (HF exposure) conditions. The system was also designed to ensure the safe handling and application of HF. An initial system calibration introduced HF gas into the exposure chamber and monitored HF concentrations by cavity ring-down spectroscopy for a 48-h period. Stable concentrations inside the exposure chamber were observed after approximately 15 h, and losses of HF to the system ranged from 88 to 91%. A model plant species (Festuca arundinacea) was then exposed to HF for 48 h. Visual phenotype stress-induced responses aligned with symptoms reported in the literature for fluoride exposure (tip dieback and discoloration along the dieback transition margin). Fluoride concentrations in exposed tissues compared to control tissues confirmed enhanced fluoride uptake due to HF exposure. The system described herein can be applied to other reactive atmospheric pollutants of interest in support of bioindicator research. [ABSTRACT FROM AUTHOR]

Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment. These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport. [ABSTRACT FROM AUTHOR]

Single particle cavity ring-down spectroscopy (CRDS) allows direct and continuous measurements of the extinction cross-sections for levitated micron-scale aerosol particles of constant or evolving composition. Our recent interests have concerned single particle CRDS measurements for light-absorbing particles. These measurements are made on single, spherical particles evaporating over the radius range 1500–700 nm that are levitated within a 405-nm cavity ring-down spectrometer using a linear electrodynamic quadrupole trap. Here, we quantify the accuracy and precision of our cavity ring-down time measurements and the consequences of particle motion within our electrodynamic trap. Next, we estimate the uncertainty in our particle size retrievals from angularly resolved elastic light scattering measurements for particles with a range of absorption strengths. Finally, we assess the accuracy of complex refractive index values retrieved from simultaneous ring-down time and particle size measurements. The assessments account for the impacts of shot and detector noise in the measured ring-down times, the driven particle motion within the electrodynamic trap, and particle absorption strength (for imaginary refractive indices in the range ∼0.0–0.1). The real and imaginary refractive indices are retrieved to an accuracy better than 0.005 and 0.002, respectively, for almost all absorption strengths studied, and for particles of constant or evolving composition. Although particles confined in our electrodynamic quadrupole trap undergo considerable levels of driven motion (with oscillation amplitudes of several tens of micrometers), the contribution of this motion to uncertainty in retrieved refractive indices is negligible compared to contributions from particle sizing errors. [ABSTRACT FROM AUTHOR]

Dark CO2 fixation by bacteria is believed to be particularly important in oligotrophic ecosystems. However, only a few studies have characterized the role of bacterial dissolved inorganic carbon (DIC) fixation in global carbon dynamics. Therefore, this study quantified the primary production (PP), total bacteria dark CO2 fixation (TBDIC fixation), and heterotrophic bacterial production (HBP) in the warm and oligotrophic Red Sea using stable isotope labeling and cavity ring-down spectroscopy (13C-CRDS). Additionally, we assessed the contribution of bacterial DIC fixation (TBDIC %) relative to the total DIC fixation (TotalDIC fixation). Our study demonstrated that TBDIC fixation increased the TotalDIC fixation from 2.03 to 60.45 µg C L-1 d-1 within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 ± 0.02 % of the photic layer TotalDIC fixation. The highest TBDIC fixation values were measured at the surface and deep (400 m) water with an average value of 5.23 ± 0.45 µg C L-1 d-1, and 4.95 ± 1.33 µg C L-1 d-1, respectively. These findings suggest that the non-photosynthetic processes such as anaplerotic DIC reactions and chemo-autotrophic CO2 fixation extended to the entire oxygenated water column. On the other hand, the % of TBDIC contribution to TotalDIC fixation increased as primary production decreased (R² = 0.45, p <0.0001), suggesting the relevance of increased dark DIC fixation when photosynthetic production was low or absent, as observed in other systems. Therefore, when estimating the total carbon dioxide production in the ocean, dark DIC fixation must also be accounted as a crucial component of the carbon dioxide flux in addition to photosynthesis. [ABSTRACT FROM AUTHOR]

Reported here are portions of the infrared absorption cross section for methanol (CH3OH), as measured by frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) at wavelengths near λ = 2.0 µm. High-resolution spectra of two gravimetric mixtures of CH3OH-in-air with nominal mole fractions of 202.2 µmol/mol and 45.89 µmol/mol, respectively, were recorded at pressures between 0.8 kPa and 102 kPa and at a temperature of 298 K. Covering the experimental wavenumber range of 4990 cm−1 to 5010 cm−1 in increments of 0.0067 cm−1 and with an instrument linewidth of 30 kHz, we observed an evolution in the CH3OH spectrum from resolved absorption lines at a low pressure (0.833 kPa) to a pseudocontinuum of absorption at a near-atmospheric pressure (101.575 kPa). An analysis of resolvable features at the lowest recorded pressure yielded a minimum intramolecular vibrational energy redistribution (IVR) lifetime for the OH-stretch (ν1) plus OH-bend (ν6) combination of τIVR ≥ 232 ps—long compared to other methanol overtones and combinations. Consequently, we show that high-resolution FS-CRDS of this relatively weak CH3OH combination band provided an additional avenue by which to study the intramolecular dynamics of this simplest organic molecule with hindered internal rotation. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of near-resonant, rovibrational two-photon spectroscopy and the use of cavity ring-down spectroscopy for its detection. Expressions are derived for the photon absorption rate of a three-level system, correct to all orders and the simpler expressions that result from various approximations. The analysis includes the angular momentum projection degeneracies and linear or circular polarization of the exciting field. Expressions are derived for the rate of two-photon power loss for light inside a resonant cavity. Explicit calculations are made for excitation of the ν3 mode of 12C16O2 for which the two-photon excitation spectrum is dominated by a single v3 = 0 → 2, Q(16) line at ν ̃ = 2335.826 cm−1. This transition has an intermediate v3 = 0 → 1, P(16) one-photon transition that is off resonance by 0.093 cm−1 (2.8 GHz). At 1 Torr total pressure, the Q(16) two-photon transition is calculated to have a cross section of 2.99 × 10−38 cm4 s per CO2 molecule in the J = 16 state or 2.24 × 10−39 cm4 s per CO2 molecule at 300 K. The analysis of the sensitivity limits for 2-photon cavity ring-down spectroscopy predicts a theoretical detection limit of 32 ppq (10−15) Hz−1/2 for 12C16O2, higher sensitivity than has been realized using one-photon absorption. The analysis predicts that most polyatomic molecules will have sparse, Doppler-free two-photon absorption spectra, which will dramatically increase the selectivity of trace gas detection of samples with multiple components with overlapping absorption bands. This is demonstrated by the predicted mid-IR two-photon absorption spectrum of butadiene using theoretical spectroscopic constants. [ABSTRACT FROM AUTHOR]

Cavity ring-down spectroscopy (CRDS) is a well-established, highly sensitive absorption technique whose sensitivity and selectivity for trace radical sensing can be further enhanced by measuring the polarization rotation of the intracavity light by the paramagnetic samples in the presence of a magnetic field. In this paper, we highlight the use of this Faraday rotation cavity ring-down spectroscopy (FR-CRDS) for the detection of HO2 radicals. In particular, we use a cold atmospheric pressure plasma jet as a highly efficient source of HO2 radicals and show that FR-CRDS in the near-infrared spectral region (1506 nm) has the potential to be a useful tool for studying radical chemistry. By simultaneously measuring ring-down times of orthogonal linearly polarized light, measurements of Faraday effect-induced rotation angles (θ) and absorption coefficients (α) are retrieved from the same data set. The Faraday rotation measurement exhibits better long-term stability and enhanced sensitivity due to its differential nature, whereby highly correlated noise between the two channels and slow drifts cancel out. The bandwidth-normalized sensitivities are α m i n = 2.2 × 1 0 − 11 cm − 1 Hz − 1 / 2 and θ m i n = 0.62 nrad Hz − 1 / 2 . The latter corresponds to a minimum detectable (circular) birefringence of Δ n m i n = 5 × 1 0 − 16 Hz − 1 / 2 . Using the overlapping qQ3(N = 4–9) transitions of HO2, we estimate limits of detection of 3.1 × 108 cm−3 based on traditional (absorption) CRDS methods and 6.7 × 107 cm−3 using FR-CRDS detection, where each point of the spectrum was acquired during 2 s. In addition, Verdet constants for pertinent carrier (He, Ar) and bulk (N2, O2) gases were recorded in this spectral region for the first time. These show good agreement with recent measurements of air and values extrapolated from reported Verdet constants at shorter wavelengths, demonstrating the potential of FR-CRDS for measurements of very weak Faraday effects and providing a quantitative validation to the computed rotation angles. [ABSTRACT FROM AUTHOR]

Intracavity optogalvanic detection of 14C utilizes the narrow band specificity of 14CO2 laser resonances in the infrared spectrum, coupled with greatly enhanced sensitivity from amplified effective path lengths in optical cavities. Background (nonresonant) interactions are also enhanced in such cavities, making proper separation of signals from background imperative. Intracavity Optogalvanic Spectroscopy (ICOGS) is similar to cavity ring-down spectroscopy (CRDS) with certain crucial differences. An ICOGS model, based on a basic CO2 laser and optogalvanic effect physics, is presented. Experimental results using a laboratory instrument with a continuous flow of small CO2 samples in a buffer gas illustrate the model. It is shown that acquisition of optimized signal-to-background ratios for the quantitation of 14CO2 in samples of order 10 μg is achievable, considerably smaller than with CRDS. [ABSTRACT FROM AUTHOR]