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• An innovative slit nozzle with adjustable opening is used to cool C2H4 down to 6 K. • Cavity ring-down spectroscopy provides high sensitivity in the 1.6–1.7 µm range. • Rotational cooling allows observation of 14 new vibrational bands. • 320 rovibrational lines are assigned to 20 bands using the TheoReTS linelist. Absorption spectra of jet-cooled ethylene (ethene, C 2 H 4) are recorded at three different rotational temperatures (6/8 K, 12 K, 38 K) using cavity ring-down spectroscopy (CRDS) in the 5880–6200 cm−1 spectral region. Rotational cooling is used to determine the various vibrational band centers by simplifying drastically the rotational band structure. A line-by-line assignment, based on a direct comparison with the TheoReTS variational line list and a systematic use of lower state combination difference (LSCD), is performed. Experimental line lists including line position and line integrated absorption cross sections are drawn up. The 6/8 K, 12 K and 38 K spectra contain 668, 1553 and 1679 absorption lines respectively. Overall, 320 rovibrational lines are assigned across 20 interacting vibrational bands. Among the 20 vibrational cold bands identified in this work, 14 had never been observed before. Line intensities are in the range of 10−24 - 10−20 cm/molecule. A direct comparison between our work and the TheoReTS and ExoMol theoretical line lists, as well as with the recent experimental work of Ben Fathallah et al. (2024) is provided. [ABSTRACT FROM AUTHOR]

The characteristics of the CISE-LOCEAN seawater isotope dataset (δ18 O, δ2 H, referred to as δ D) are presented (10.17882/71186; Waterisotopes-CISE-LOCEAN, 2021). This dataset covers the time period from 1998 to 2021 and currently includes close to 8000 data entries, all with δ18 O, three-quarters of them also with δ D, associated with a date stamp, space stamp, and usually a salinity measurement. Until 2010, samples were analyzed by isotopic ratio mass spectrometry and since then mostly by cavity ring-down spectroscopy (CRDS). Instrumental uncertainty in this dataset is usually as low as 0.03 ‰ for δ18 O and 0.15 ‰ for δ D. An additional uncertainty is related to the isotopic composition of the in-house standards that are used to convert data to the Vienna Standard Mean Ocean Water (VSMOW) scale. Different comparisons suggest that since 2010 the latter have remained within at most 0.03 ‰ for δ18 O and 0.20 ‰ for δ D. Therefore, combining the two uncertainties suggests a standard deviation of at most 0.05 ‰ for δ18 O and 0.25 ‰ for δ D. For some samples, we find that there has been evaporation during collection and storage, requiring adjustment of the isotopic data produced by CRDS, based on d -excess (δ D - 8×δ18 O). This adjustment adds an uncertainty in the respective data of roughly 0.05 ‰ for δ18 O and 0.10 ‰ for δ D. This issue of conservation of samples is certainly a strong source of quality loss for parts of the database, and "small" effects may have remained undetected. The internal consistency of the database can be tested for subsets of the dataset when time series can be obtained (such as in the southern Indian Ocean or North Atlantic subpolar gyre). These comparisons suggest that the overall uncertainty of the spatially (for a cruise) or temporally (over a year) averaged data is less than 0.03 ‰ for δ18 O and 0.15 ‰ for δ D. However, 18 comparisons with duplicate seawater data analyzed in other laboratories or with other datasets in the intermediate and deep ocean suggest a larger scatter. When averaging the 18 comparisons done for δ18 O, we find a difference of 0.082 ‰ with a standard error of 0.016 ‰. Such an average difference is expected due to the adjustments applied at LOCEAN to saline water data produced either by CRDS or isotope ratio mass spectrometry (IRMS), but the scatter found suggests that care is needed when merging datasets from different laboratories. Examples of time series in the surface North Atlantic subpolar gyre illustrate the temporal changes in water isotope composition that can be detected with a carefully validated dataset. [ABSTRACT FROM AUTHOR]

Water vapor absorption in the near-ultraviolet region is essential to describe the energy budget of Earth, but little spectroscopic information is available since it is a challenging spectral region for both experimental and theoretical studies. A continuous-wave cavity ring-down spectroscopic experiment was built to record absorption lines of water vapor around 415 nm. With a minimum detectable absorption coefficient of 4×10-10 cm-1, 40 rovibrational transitions of H162O were observed in this work, and 27 of them were assigned to the (224), (205), (710), (304), (093), (125), and (531) vibrational bands. A comparison of line positions and intensities determined in this work to the most recent HITRAN database is presented. Water vapor absorption cross-sections near 415 nm were calculated based on our measurements, which vary between 1×10-26 and 5×10-26 cm²/molecule. These data will also significantly impact the spectroscopy detection of trace gas species in the near-UV region. [ABSTRACT FROM AUTHOR]

The development of mid-infrared (mid-IR) tunable lasers has been driving various laser spectroscopic technologies. Herein, we report wavelength-scanning cavity ring-down spectroscopy (WS-CRDS) in the mid-IR region using an electronically tuned Cr:ZnSe (ET-Cr:ZnSe) laser, which could achieve a nanosecond pulse operation, with broad wavelength tuning of 2–3 µm. This allowed WS-CRDS-induced trace detection of the refrigerant, CH2F2. A CH2F2 detection limit of 0.66 ppm (3σ), and the detection of trace H2O in CH2F2 was realized using the broad wavelength-tuning range feature, demonstrating the effectiveness of the ET-Cr:ZnSe laser in WS-CRDS. We believe that our method would accelerate the development of various trace-gas detection technologies. [ABSTRACT FROM AUTHOR]

Spectroscopic gas sensing technologies based on absorption and Raman scattering are fast, nondestructive, long-term stable and highly selective. By making use of an optically resonant cavity, the sensitivity can be enhanced hundreds to thousands of times. However, frequency-locking technology is necessary to maintain a stable resonant condition. In this review, various applications of Pound-Drever-Hall (PDH) and optical feedback (OF) frequency-locking cavity-enhanced spectroscopy (cavity ring-down spectroscopy, cavity-enhanced absorption spectroscopy and cavity-enhanced Raman spectroscopy) for highly sensitive gas sensing are presented. The effect of frequency-locking cavity-enhanced spectroscopy for improving the sensitivity of gas sensing is demonstrated. In addition, the key parameters and advantages as well as limitations of different frequency-locking cavity-enhanced spectroscopy are summarized and discussed. [ABSTRACT FROM AUTHOR]

Comprehensive observations of the nocturnal atmospheric oxidation of NO 3 and N 2 O 5 were conducted at a suburban site in Changzhou in the YRD using cavity ring-down spectroscopy (CRDS) from 27 May to 24 June, 2019. High concentrations of NO 3 precursors were observed, and the nocturnal production rate of NO 3 was determined to be 1.7 ± 1.2 ppbv/hr. However, the nighttime NO 3 and N 2 O 5 concentrations were relatively low, with maximum values of 17.7 and 304.7 pptv, respectively, illustrating the rapid loss of NO 3 and N 2 O 5. It was found that NO 3 dominated the nighttime atmospheric oxidation, accounting for 50.7%, while O 3 and OH only contributed 34.1% and 15.2%, respectively. For the reactions of NO 3 with volatile organic compounds (VOCs), styrene was found to account for 60.3%, highlighting its dominant role in the NO 3 reactivity. In general, the contributions of the reactions between NO 3 and VOCs and the N 2 O 5 uptake to NO 3 loss were found to be about 39.5% and 60.5%, respectively, indicating that N 2 O 5 uptake also played an important role in the loss of NO 3 and N 2 O 5 , especially under the high humidity conditions in China. The formation of nitrate at night mainly originated from N 2 O 5 uptake, and the maximum production rate of NO 3 − reached 6.5 ppbv/hr. The average NO x consumption rate via NO 3 and N 2 O 5 chemistry was found to be 0.4 ppbv/h, accounting for 47.9% of the total NO x removal. The predominant roles of NO 3 and N 2 O 5 in nitrate formation and NOx removal in the YRD region was highlighted in this study. [Display omitted] [ABSTRACT FROM AUTHOR]

A new method of using cavity ringdown spectroscopy (CRDS) technique to measure apparent electron impact excitation cross-sections (EIECS) for different energy levels of an atom is described. The method involves measurements of absolute population densities of the energy levels in concern using the high sensitivity CRDS, leading to an analytical expression of EIECS as a function of the population densities. Determination of EIECS in this method does not require an external calibration. The proposed method is validated by determining EIECS of the metastable levels of Hg (6s6p 3 P 0 ) and Ne (2p 5 3s 3 P 2 ), and the results are in good agreement with the cross-sections reported in the literature. The population densities in both cases were extracted from the published data. This method exhibits promising potential for absolute measurements of EIECS of metastable energy levels. [ABSTRACT FROM AUTHOR]

Cavity ring-down spectroscopy is a ubiquitous optical method used to study light-matter interactions with high resolution, sensitivity and accuracy. However, it has never been performed with the multiplexing advantages of direct frequency comb spectroscopy without significantly compromising spectral resolution. We present dual-comb cavity ring-down spectroscopy (DC-CRDS) based on the parallel heterodyne detection of ring-down signals with a local oscillator comb to yield absorption and dispersion spectra. These spectra are obtained from widths and positions of cavity modes. We present two approaches which leverage the dynamic cavity response to coherently or randomly driven changes in the amplitude or frequency of the probe field. Both techniques yield accurate spectra of methane—an important greenhouse gas and breath biomarker. When combined with broadband frequency combs, the high sensitivity, spectral resolution and accuracy of our DC-CRDS technique shows promise for applications like studies of the structure and dynamics of large molecules, multispecies trace gas detection and isotopic composition. [ABSTRACT FROM AUTHOR]

The characteristics of the CISE-LOCEAN sea water isotope data set (δ18O, δ²H, later designed as δD) are presented. This data set covers the time period from 1998 to 2021 and currently includes close to 8000 data entries, all with δ18O, three quarters of them also with δD, associated with a time and space stamp and usually a salinity measurement. Until 2010, samples were analysed by isotopic ratio mass spectrometry, and since then mostly by cavity ring-down spectroscopy (CRDS). Instrumental uncertainty on individual data in this dataset is usually with a standard deviation as low as 0.03 / 0.15 ‰ for δ18O and δD. An additional uncertainty is related to uncertain isotopic composition of the in-house standards that are used to convert daily data into the VSMOW scale. Different comparisons suggest that since 2010 the latter have remained within at most 0.03 / 0.20 ‰ for δ18O and δD. Therefore, combining the two suggests a standard deviation of at most 0.05 / 0.25 ‰ for δ18O / δD. Finally, for some samples, we find that there has been evaporation during collection and storage, requiring adjustment of the isotopic data produced by CRDS, based on d-excess. This adds an uncertainty on the adjusted data of roughly 0.05 / 0.10 ‰ on δ18O and δD. This issue of conservation of samples is certainly a strong source of quality loss for parts of the database, and 'small' effects may have remained undetected. The internal consistency of the database can be tested for subsets of the dataset, when time series can be obtained (such as in the southern Indian Ocean or North Atlantic subpolar gyre). These comparisons suggest that the overall uncertainty of the spatially (for a cruise) or temporally (over a year) averaged data is on the order of or less than 0.03 / 0.15 ‰ for δ18O / δD. On the other hand, 17 comparisons with duplicate sea water data analysed in other laboratories or with other data sets in deep regions suggest a larger scatter. When averaging the 17 comparisons done for δ18O, we find a difference close to the adjustment applied at LOCEAN to convert salty water data from the activity to the concentration scale. Such a difference is expected, but the scatter found suggests that care is needed when merging datasets from different laboratories. Examples of time series in the surface North Atlantic subpolar gyre illustrate the temporal changes in water isotope composition that can be detected with a carefully validated dataset. [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]

Surface air discharge has been extensively reported to have strong antibacterial and anticancer effects, and these biological effects are more or less attributed to the short-lived aqueous reactive species produced by the air plasma. Insight into the generation mechanism for short-lived species is a key bottleneck in elucidating the antimicrobial and anticancer effects. Although the numerical study has predicted that the dissolution of gaseous NO3 plays a crucial role, but so far without experimental validation. In view of this, cavity ring-down spectroscopy is adopted in this paper to measure the NO3 spatial distribution between the surface air discharge and the solutions to be treated, and the concentrations of short-lived species in the solutions after plasma treatment are also measured for different discharge modes. A simplified chemical pathway for the conversion of gaseous NO3 to aqueous ONOOaq−/ONOOHaq and O2aq− is proposed. Moreover, the inactivation effects for Escherichia coli and A549 lung cancer cells treated by the plasma-activated solutions are measured for different concentrations of short-lived species, and the key species for sterilization and anticancer are identified by chemical scavengers. Finally, a positive correlation chain is found among the inactivation effect, the concentrations of aqueous ONOOaq−/ONOOHaq and O2aq−, and the density of gaseous NO3, implying that NO3 might be very important for the production of aqueous short-lived reactive species as well as the biological effects induced by plasma-activated solutions. [ABSTRACT FROM AUTHOR]

Summary: This study investigated the carbon isotope ratio (¹³C/¹²C, δ13C in unit of parts per thousand or per mill, ‰) of different coconut water samples using elemental analysis isotope ratio mass spectrometry (EA‐IRMS) and combustion module cavity ring‐down spectroscopy (CM‐CRDS). Natural coconut water from young coconuts from 12 provinces in Thailand (n = 94), adulterated coconut water containing three sweeteners (sucrose, glucose and fructose) at different concentrations and eight brands of commercial coconut water were analysed. The δ13C of all samples were not significantly different (P > 0.05) between the EA‐IRMS and CM‐CRDS analyses. The natural coconut water (C3 plant) had δ13C ranging from −21.58‰ to −27.79‰ (mean −24.64 ± 0.91‰). Three sweeteners (C4 plant) contained δ13C between −11.46‰ to −13.16‰. The use of δ13C determination can detect adulteration of a singular extraneous sweetener (either glucose or sucrose) down to a level of 2% of adulteration. For the detected δ13C values of commercial products labelled as 'no added sugar', about 50% of products were adulterated. This study demonstrates that CM‐CRDS can be used as an alternative analytical platform to EA‐IRMS for detecting adulterated products, especially coconut water. [ABSTRACT FROM AUTHOR]

The traditional photoacoustic cavity has the advantages of simple structure, low cost, and easy integration with optical cavity technology, so it has significant advantages in the measurement of the optical characteristics of respirable dust. In order to meet the demand of high-precision respirable dust measurements in practical applications, it is necessary to improve the measurement accuracy of respirable dust by traditional photoacoustic spectroscopy technology. Therefore, the structure size of the photoacoustic cavity was determined by theoretical and simulation analysis. A system for measuring respirable dust by photoacoustic spectroscopy was designed, which was applied to the atmospheric respirable dust detection simultaneously with the cavity ring-down spectroscopy system. The results showed that the correlation between the two systems was poor. Therefore, the three-layer back propagation neural network algorithm was used to correct the photoacoustic response values, and the measured value of the cavity ring-down spectroscopy system was used as the reference truth value. The calibration results showed that the output value of the neural network model was in good agreement with the reference true value: the slope was above 0.96. The results showed that the neural network algorithm could effectively improve the measurement accuracy of the photoacoustic spectroscopy system to respirable dust, improve the linearity, and reduce the detection error. [ABSTRACT FROM AUTHOR]

Rationale: This study determines if saliva collection procedures for the doubly labeled water (DLW) method, used for measuring total energy expenditure (TEE), are comparable to urine and plasma collection. Both the cavity ring-down spectroscopy (CRDS) and isotope ratio mass spectrometry (IRMS) analyses techniques are compared. Methods: Saliva specimens were collected from participants for the DLW method. The specimens were collected under different conditions: after consumption of tap water, after chewing gum, and during exposure to conditions of high and low relative humidity. The isotopes in saliva were compared with simultaneous plasma and urine collection. TEE calculated from saliva and analyzed using CRDS was compared to that of plasma analyzed using IRMS. Results: The within-individual variances were not significantly different between the saliva specimens (0.4%) and plasma (0.3%). After the oral dose of DLW, the saliva specimens displayed a shorter equilibration time to urine. When participants consumed 500 mL of tap water, the enrichment of saliva specimens reached a new plateau value faster than urine. Saliva collection exposed to high ambient humidity conditions was slightly less enriched as compared to low-humidity conditions while urine enrichment was unaffected. In contrast, whereas the within-individual effects of gum chewing during saliva collection on 18O were unaffected, the abundance of 2H in saliva was slightly lower after chewing the gum. The within-individual difference between TEE calculated from saliva and that calculated from plasma analyzed using IRMS did not differ from zero, and the standard deviation was not different from that predicted by a propagation of error analysis based on analytical error alone. Conclusions: Our findings support using saliva specimens for the DLW method. The analysis of plasma and urine, however, requires reducing the memory effect resulting from contaminants. Also, it should be performed in a manner that minimizes exposure to air where specimens may be exposed to evaporation or contamination from water vapor during sampling. [ABSTRACT FROM AUTHOR]

Determining the fate of CO2 respired in woody tissues is necessary to understand plant respiratory physiology and to evaluate CO2 recycling mechanisms. An aqueous 13C‐enriched CO2 solution was infused into the stem of 3–4 m tall trees to estimate efflux and assimilation of xylem‐transported CO2 via cavity ring‐down laser spectroscopy and isotope ratio mass spectrometry, respectively. Different tree locations (lower stem, upper stem and leafy shoots) and tissues (xylem, bark and leaves) were monitored in species with tracheid, diffuse‐ and ring‐porous wood anatomy (cedar, maple and oak, respectively). Radial xylem CO2 diffusivity and xylem [CO2] were lower in cedar relative to maple and oak trees, thereby limiting label diffusion. Part of the labeled 13CO2 was assimilated in cedar (8.7%) and oak (20.6%) trees, mostly in xylem and bark tissues of the stem, while limited solution uptake in maple trees hindered the detection of label assimilation. Little label reached foliar tissues, suggesting substantial label loss along the stem‐branch transition following reductions in the radial diffusive pathway. Differences in respiration rates and radial xylem CO2 diffusivity (lower in conifer relative to angiosperm species) might reconcile discrepancies in efflux and assimilation of xylem‐transported CO2 so far observed between taxonomic clades. Xylem CO2 diffusivity, estimated with an isotopic mass balance, and xylem [CO2] were lower in cedar relative to maple and oak trees. These observations help to reconcile discrepancies in efflux and assimilation of xylem‐transported CO2 so far observed between conifer and angiosperm species. [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]

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]

We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of a-pinene, 2-butanol, and a-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces. [ABSTRACT FROM AUTHOR]

We integrated a rigid optical trap into a tunable pulsed cavity ringdown spectroscopy (OT-CRDS) system to characterize the extinction of single airborne particles in the UV spectral region (306-315 nm). Single solid particles from a multi-walled carbon nanotube (MWCNT), Bermuda grass smut spore, carbon microsphere, and blackened polyethylene microsphere were trapped in air based on the photophoretic force. The improved OT-CRDS system was highly sensitive and able to resolve extinctions of single particles from different materials and sizes at a given wavelength. Further, we successfully manipulated the number of particles, e.g., 1, 2 or more particles, in the trap and measured their distinguishable extinctions using the OT-CRDS. We also show that the particle size and extinction have a good linear correlation from the measurements of 24 single MWCNT particles. Material- and wavelength-dependent extinctions of the four types of airborne particles were also characterized. Results reveal that single airborne particles regardless of their differences in material and size, due to their heterogeneous morphology, have individual-particle dependent extinctions and that dependence can be resolved and characterized using the OT-CRDS technique.

Near-infrared cavity ringdown spectra were recorded following the photolysis of dihalomethanes in O 2 /N 2 mixtures. In particular, photolysis of CH 2 I 2 under conditions previously reported to produce the simplest Criegee intermediate, CH 2 O 2 , gave a complex, structured spectrum between 6800 and 9000 cm -1 , where the lowest triplet-singlet transition (ã-X̃) of CH 2 O 2 might be expected. To help identify the carrier of the spectrum, extensive electronic structure calculations were performed on the ã and X̃ states of CH 2 O 2 and the lowest two doublet states of the iodomethylperoxy radical, CH 2 IO 2 , which also could be produced by the chemistry and whose Ã-X̃ transition likely lies in this spectral region. The conclusion of these calculations is that the ã-X̃ transition of CH 2 O 2 clearly falls outside the observed spectral range and would be extremely weak both because it is spin-forbidden and because of a large geometric change between the ã and X̃ states. Moreover, only a shallow well (with a barrier to dissociation of less than 1900 cm -1 ) is predicted on the ã state, which likely precludes the existence of long-lived states. Calculations for the Ã-X̃ transition of CH 2 IO 2 are generally consistent with the observed spectrum in terms of both the electronic origin and vibrational frequencies in the à state. To confirm the carrier assignment to CH 2 IO 2 , calculations beyond the Franck-Condon approximation were carried out to explain the hot band structure of the large-amplitude, low-frequency O-O-C-I torsion mode, ν 12 . Photolysis of other dihalomethanes produced similar spectra which were analyzed and assigned to CH 2 ClO 2 and CH 2 BrO 2 . Experimental values for the electronic energies and frequencies for several à state vibrations and the ν 12 vibration of the X̃ state of each are reported. In addition, the observed spectra were used to follow the self-reaction of the CH 2 IO 2 species and its reaction with SO 2 . The rates of these reactions are dramatically faster than those of unsubstituted alkyl peroxy radicals and approach those of the Criegee intermediate.

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO 2) is NO-O 3 chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NO x (= sum of NO and NO 2) are measured by converting NO 2 to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO 2 by P-CL was investigated. Results with two photolytic NO 2 converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO 2 , NO x and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO 2 conversion efficiency (CF NO2 ; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s-1 and 2.9 s-1 for NO 2 and 0.25 s-1 and 0.10 s−1 for HONO at 395 nm and 415 nm, respectively. CF HONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO 2 by P-CL marginally but systematically overestimate true NO 2 concentrations, and that this interference should be considered in environments with high HONO:NO 2 ratios such as the marine boundary layer or in biomass burning plumes. [Display omitted] [ABSTRACT FROM AUTHOR]

Photoacoustic spectroscopy technology is an important method to detect the concentration of trace gases, so it is of great significance to improve the detection accuracy of the photoacoustic spectroscopy system (PAS). In this paper, a multiple linear regression algorithm was proposed to correct the accuracy of the PAS based on the high-precision cavity ring-down spectroscopy measurement system. The results showed that the correlation coefficient R2 between the corrected values of the multiple linear regression model and the reference true values was 0.903. It can be seen that the algorithm can effectively improve the detection accuracy of the PAS. A comparative experiment was carried out with the long optical path differential absorption spectroscopy system (LP-DOAS) for measuring the NO2 concentration in an ambient atmosphere. The experimental results showed that the corrected PAS and the LP-DOAS had a good correlation in measuring the NO2 concentration, the slope of linear fitting was 1.012 ± 0.040, and the correlation coefficient was 0.948. [ABSTRACT FROM AUTHOR]

We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO 3) in a 1 m 3 Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO 2), which is monitored by cavity ring-down spectroscopy (TD-CRDS). Using thermal dissociation inlets (TDIs) made of quartz, the temperature-dependent dissociation profiles (thermograms) of ISOP-NITs measured in the presence of ozone (O 3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for, for example, isopropyl nitrate (iPN) or peroxy acetyl nitrate (PAN) under the same conditions. The shape of the thermograms varied with the TDI's surface-to-volume ratio and with material of the inlet walls, providing clear evidence that ozone and quartz surfaces catalyse the dissociation of unsaturated organic nitrates leading to formation of NO 2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). The use of a TDI consisting of a non-reactive material suppresses the conversion of isoprene-derived ANs at 473 K, thus allowing selective detection of PNs. The potential for interference by the thermolysis of nitric acid (HNO 3), nitrous acid (HONO) and O 3 is assessed. [ABSTRACT FROM AUTHOR]

Rationale: The precision obtained in routine isotope analysis of water (δ17O, δ18O, δ2H, 17O‐excess and d‐excess values) using cavity ring‐down spectroscopy is usually below the instrument specifications provided by the manufacturer. This study aimed at reducing this discrepancy, with particular attention paid to mitigating the memory effect (ME). Methods: We used a Picarro L2140i analyzer coupled with a high‐precision A0211 vaporizer and an A0325 autosampler. The magnitude and duration of the ME were estimated using 24 series of 50 successive injections of samples with contrasting compositions. Four memory correction methods were compared, and the instrument performance was evaluated over a 17‐month period of routine analysis, using two different run architectures. Results: The ME remains detectable after the 30th injection, implying that common correction procedures only based on the last preceding sample need to be revised. We developed a new ME correction based on the composition of several successive samples, and designed a run architecture to minimize the magnitude of the ME. The standard deviation obtained from routine measurement of a quality assurance water sample over a seven‐month period was 0.015‰ for δ17O, 0.023‰ for δ18O, 0.078‰ for δ2H, 0.006‰ for 17O‐excess and 0.173‰ for d‐excess. In addition, we provided the first δ17O and 17O‐excess values for the GRESP certified reference material. Conclusions: This study demonstrates the long‐term persistence of the ME, which is often overlooked in routine analysis of natural samples. As already evidenced when measuring labelled water, it calls for consideration of the compositions of several previous samples to obtain an appropriate correction, a prerequisite to achieve high‐precision data. [ABSTRACT FROM AUTHOR]

The gas-phase kinetics of phenyl radical (·C6H5) with ethyl formate (HCO2Et, EF) was investigated experimentally using ultrasensitive laser-based cavity ring-down spectroscopy (CRDS). Phenyl radicals were generated by photolyzing nitrosobenzene (C6H5NO) at 248 nm and thereby probed at 504.8 nm. The rate coefficients for the (phenyl radical + EF) reaction were investigated between the temperatures of 260 and 361 K and at a pressure of 61 Torr with nitrogen (N2) as diluent. The temperature-dependent Arrhenius expression for the test reaction was obtained as: k phenyl + EF Expt , 260 - 361 K =(1.20 ± 0.16) × 10–13 exp[−(435.6 ± 50.0)/T] cm3 molecule−1 s−1 and the rate coefficient at room temperature was measured out to be: k phenyl + EF Expt , 298 K =(4.54 ± 0.42) × 10–14 cm3 molecule−1 s−1. The effects of pressure and laser fluence on the kinetics of the test reaction were found to be negligible within the experimental uncertainties. To complement the experimental findings, kinetics for the reaction of phenyl radicals with EF was investigated theoretically using Canonical Variational Transition State Theory (CVT) with Small Curvature Tunnelling (SCT) at CCSD(T)/cc-pVDZ//B3LYP/6–31 + G(d,p) level of theory in the temperatures between 200 and 400 K. The theoretically calculated rate coefficients for the title reaction were expressed in the Arrhenius form as: k phenyl + EF Theory , 200 - 400 K = (1.48 ± 0.56) × 10–38 × T8.47 × exp[(2431.3 ± 322.0)/T] cm3 molecule−1 s−1 and the corresponding rate coefficient at room temperature was calculated to be: k phenyl + EF Theory , 298 K = 4.91 × 10–14 cm3 molecule−1 s−1. A very good agreement was observed between the experimentally measured and theoretically calculated rate coefficients at 298 K. Thermochemical parameters as well as branching ratios for the reaction of (phenyl radical + EF) are also discussed in this manuscript. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (14NO 2) exhibits a unique doublet structure due to the presence of its unpaired electron, which results in a nonzero electronic angular momentum in the ground electronic state of the molecule. In this study, an investigation into high-resolution rovibrational spectral features associated with the spin-rotation doublets of 14NO 2 was conducted using an external-cavity quantum cascade laser (EC-QCL)-coupled cavity ring-down spectrometer operating at 6.2 μm. Four spin-split doublets belonging to the RR branch of the (0 0 1)-(0 0 0) fundamental band were probed in the mid-IR spectral region. The air broadening and self-broadening coefficients were reported explicitly for each doublet component for the first time, to the best of our knowledge. The line-intensities were also quantified, and they were compared to the HITRAN database, revealing good agreement (<4% discrepancy). [ABSTRACT FROM AUTHOR]

We present the results of the spectral line-shape study of the first measurement of the extremely weak (7–0) band of the 12C16O molecule. Measurements were done with a highly sensitive cavity ring-down spectrometer. Collisional narrowing, analyzed in terms of speed-dependent effects, was observed for the first time for transitions with line intensities below 2 ⋅ 1 0 − 29 cm/molecule at 296 K. We provide a full set of line-shape parameters of the speed-dependent and regular Voigt profile analysis for 14 transitions from P and R branches. Experimental verification of a strong vibrational dependence of the pressure shifting described by the Hartmann model (Hartmann, 2009) is extended up to the sixth overtone highly sensitive to the model parameter. [Display omitted] • The first line-shape study of the extremely weak (7–0) band of the 12C16O molecule. • Speed-dependent effects observed for transitions with intensities below 2 ⋅ 1 0 − 29 cm/molecule. • Full set of line-shape parameters of the speed-dependent and regular Voigt profile analysis. • Experimental verification of a strong vibrational dependence of the pressure shifting described by the Hartmann model. [ABSTRACT FROM AUTHOR]