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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]

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]

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.

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]

The first characterization of the monomer bending vibrations in gaseous water clusters was conducted by using infrared cavity ringdown spectroscopy. Discrete and sequentially blue-shifted bands near 6 microns for n = 2-4 and unresolved broad features for n > 4, supporting both theoretical computations and solid-state spectroscopy results were obtained. These measurements offer a measure of the monomer distortion that accompanies sequential hydrogen bond formation.

Abstract: The absorption spectra of jet-cooled AsH2 radicals were recorded in the wavelength range of 435–510nm by cavity ringdown spectroscopy. The AsH2 radicals were produced by pulsed DC discharge in a molecular beam of a mixture of AsH3, SF6, and argon. Seven vibronic bands with fine rotational structures have been identified and assigned as the , , and (n =1–3) bands of the electronic transition. Based on the previous studies of AsH2 radical, rotational assignments and rotational term values for each band were obtained, and the molecular parameters including vibrational constants, rotational constants, centrifugal distortion constants, and spin–rotation interaction constants were also determined. [Copyright &y& Elsevier]

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]

We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO3) in a 1 m³ Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO2), 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 (O3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for e.g. 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 NO2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). We present a simple, viable solution to this problem and discuss the potential for interference by the thermolysis of nitric acid (HNO3), nitrous acid (HONO) and O3. [ABSTRACT FROM AUTHOR]

Background: Objective dietary biomarkers are urgently needed for a wider range of foods and nutrients. The breath carbon isotope ratio (CIR; measured as δ13C values) has potential as a noninvasive measure of short-term added sugar (AS) intake but has not been evaluated in a controlled-feeding study.Objective: The aim was to evaluate the effect of short-term AS intake on breath CIR in a dose-response, randomized, crossover feeding study.Methods: Six men and 6 women, aged 25 to 60 y, were randomly assigned to a balanced sequence of 5 dietary treatments. Three treatments delivered low (0 g/d), medium (75 g/d), or high (150 g/d) amounts of AS over the course of a single day's breakfast and lunch and 2 switched high and low intake amounts between breakfast and lunch. Experimental meals delivered 60% of daily energy and added-sugar targets. There was a washout period of 1-2 wk between treatments. Breath was collected at 2-h intervals from 08:00 (fasting) to 16:00 h. Breath CIR was measured using cavity ring-down spectroscopy, and the effects of dietary treatments and baseline were evaluated using multivariate linear regression.Results: Breath CIR showed a significant response to increasing AS intake at all sampling time points (all P < 0.0001), with a dose-response of 0.030 (95% CI: 0.024, 0.037) ‰/g. Fasting breath CIR (baseline) influenced postfeeding breath CIR at all sampling time points (P < 0.0001); however, effect sizes were largest in the morning. For afternoon-collected samples (14:00 and 16:00), the effect of recent AS intake (lunch) was 4-fold greater than the effect of previous added-sugar intake (breakfast).Conclusions: These findings support the potential of the breath CIR as a biomarker of short-term AS intake in healthy US adults. More work is needed to evaluate other potential dietary effects and whether multiple breath collections could capture daily AS intake. [ABSTRACT FROM AUTHOR]

Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorganism activity, among other things. Decomposition models typically underestimate rates of plant litter decomposition in drylands, suggesting the existence of additional drivers of decomposition. Attempts to reveal these drivers have predominantly focused on abiotic degradation agents, alternative moisture sources, and soil–litter mixing. The role of burrowing animals in promoting decomposition has received less attention despite greatly contributing to plant litter transfer from the harsh desert surface to the moister and nutrient-rich environment belowground. Our goal was to explore how macro-detritivore burrows affect plant litter mineralization dynamics. We introduced 13C-labeled litter belowground into (1) desert isopod (Hemilepistus reaumuri) burrows and (2) artificial burrows, and aboveground on top of (3) isopod fecal pellet mounds and (4) bare soil crust. We compared the litter mass loss between the four treatments and used cavity ring-down spectroscopy to reveal the in situ mineralization dynamics. No litter mineralization was evident during the dry summer months both above- and belowground. Following rain events, mineralization rates spiked in all four micro-environments, quickly diminishing aboveground while slowly waning belowground. Total litter mass loss was twofold higher below than aboveground and was significantly higher in isopod burrows compared to artificial burrows. Our findings demonstrate that burrowing macro-detritivores promote litter decomposition in deserts by transferring organic matter to their burrows where favorable climatic conditions and a nutrient-enriched environment foster microbial activity. Thus, attempts to resolve the dryland decomposition conundrum should not be limited to exploring factors that allow decomposition under harsh desert surface climatic conditions, but focus on the role that animals play in facilitating decomposer-friendly environments to which they translocate plant litter. [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]

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]

A well-characterized source of nitrous acid vapour (HONO) is essential for accurate ambient air measurements by instruments requiring external calibration. In this work, a compact HONO source is described in which gas streams containing dilute concentrations of HONO are generated by flowing hydrochloric acid (HCl) vapour emanating from a permeation tube over continuously agitated dry sodium nitrite (NaNO2) heated to 50 ∘ C. Mixing ratios of HONO and potential by-products including NO, NO2 , and nitrosyl chloride (ClNO) were quantified by Fourier transform infrared (FTIR) and thermal-dissociation cavity ring-down spectroscopy (TD-CRDS). A key parameter is the concentration of HCl, which needs to be kept small (<4 ppmv) to avoid ClNO formation. The source produces gas streams containing HONO in air in >95 % purity relative to other nitrogen oxides. The source output is rapidly tuneable and stabilizes within 90 min. Combined with its small size and portability, this source is highly suitable for calibration of HONO instruments in the field. [ABSTRACT FROM AUTHOR]

For the past two decades, the measurement of nitrous oxide (N2O) isotopocules – isotopically substituted molecules 14N15N16O , 15N14N16O and 14N14N18O of the main isotopic species 14N14N16O – has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), has enabled the production of commercially available and field-deployable N2O isotopic analyzers. In contrast to traditional isotope-ratio mass spectrometry (IRMS), these instruments are inherently selective for position-specific 15N substitution and provide real-time data, with minimal or no sample pretreatment, which is highly attractive for process studies. Here, we compared the performance of N2O isotope laser spectrometers with the three most common detection schemes: OA-ICOS (N2 OIA-30e-EP, ABB – Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration, trace gas extractor (TREX)-mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analyzers were then characterized for their dependence on [N2O] , gas matrix composition (O2 , Ar) and spectral interferences caused by H2O , CO2 , CH4 and CO to develop analyzer-specific correction functions. Subsequently, a simulated two-end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers. Our results show that N2O isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to N2O mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of N2O isotope laser spectrometers in order to acquire accurate N2O isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g., laboratory incubations, N2O liberated from wastewater or groundwater), as well as extend to future analyzer models and instruments focusing on isotopic species of other molecules. [ABSTRACT FROM AUTHOR]

Simultaneous measurements of CH3O2 radical concentrations have been performed using two different methods in the Leeds HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber at 295 K and in 80 mbar of a mixture of 3:1 He/O2 and 100 or 1000 mbar of synthetic air. The first detection method consisted of the indirect detection of CH3O2 using the conversion of CH3O2 into CH3O by excess NO with subsequent detection of CH3O by fluorescence assay by gas expansion (FAGE). The FAGE instrument was calibrated for CH3O2 in two ways. In the first method, a known concentration of CH3O2 was generated using the 185 nm photolysis of water vapour in synthetic air at atmospheric pressure followed by the conversion of the generated OH radicals to CH3O2 by reaction with CH4/O2. This calibration can be used for experiments performed in HIRAC at 1000 mbar in air. In the second method, calibration was achieved by generating a near steady state of CH3O2 and then switching off the photolysis lamps within HIRAC and monitoring the subsequent decay of CH3O2 , which was controlled via its self-reaction, and analysing the decay using second-order kinetics. This calibration could be used for experiments performed at all pressures. In the second detection method, CH3O2 was measured directly using cavity ring-down spectroscopy (CRDS) using the absorption at 7487.98 cm -1 in the A←X (ν12) band with the optical path along the ∼1.4 m chamber diameter. Analysis of the second-order kinetic decays of CH3O2 by self-reaction monitored by CRDS has been used for the determination of the CH3O2 absorption cross section at 7487.98 cm -1 , both at 100 mbar of air and at 80 mbar of a 3:1 He/O2 mixture, from which σCH3O2=(1.49±0.19)×10-20 cm 2 molecule -1 was determined for both pressures. The absorption spectrum of CH3O2 between 7486 and 7491 cm -1 did not change shape when the total pressure was increased to 1000 mbar, from which we determined that σCH3O2 is independent of pressure over the pressure range 100–1000 mbar in air. CH3O2 was generated in HIRAC using either the photolysis of Cl2 with UV black lamps in the presence of CH4 and O2 or the photolysis of acetone at 254 nm in the presence of O2. At 1000 mbar of synthetic air the correlation plot of [ CH3O2 ] FAGE against [ CH3O2 ] CRDS gave a gradient of 1.09±0.06. At 100 mbar of synthetic air the FAGE–CRDS correlation plot had a gradient of 0.95±0.024 , and at 80 mbar of 3:1 He/O2 mixture the correlation plot gradient was 1.03±0.05. These results provide a validation of the FAGE method to determine concentrations of CH3O2. [ABSTRACT FROM AUTHOR]

Hydroperoxyl (HO2) and organic peroxy (RO2) radicals have an unpaired spin and are highly reactive free radicals. Measurements of the sum of HO2 and RO2 provide unique information about the chemical processing in an air mass. This paper describes the experimental features and capabilities of the Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). This is an instrument designed to make measurements on aircraft from the boundary layer to the lower stratosphere. PeRCEAS combines the amplified conversion of peroxy radicals to nitrogen dioxide (NO2) with the sensitive detection of NO2 using cavity ring-down spectroscopy (CRDS) at 408 nm. PeRCEAS is a dual-channel instrument, with two identical reactor–detector lines working out of phase with one another at a constant and defined pressure lower than ambient at the aircraft altitude. The suitability of PeRCEAS for airborne measurements in the free troposphere was evaluated by extensive characterisation and calibration under atmospherically representative conditions in the laboratory. The use of alternating modes of the two instrumental channels successfully captures short-term variations in the sum of peroxy radicals, defined as RO2∗ (RO2∗=HO2+∑RO2+OH+∑RO , with R being an organic chain) in ambient air. For a 60 s measurement, the RO2∗ detection limit is < 2 pptv for a minimum (2σ) NO2 detectable mixing ratio < 60 pptv, under laboratory conditions in the range of atmospheric pressures and temperatures expected in the free troposphere. PeRCEAS has been successfully deployed within the OMO (Oxidation Mechanism Observations) and EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales) missions in different airborne campaigns aboard the High Altitude LOng range research aircraft (HALO) for the study of the composition of the free troposphere. [ABSTRACT FROM AUTHOR]

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of ~10–30 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate point-source methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as ~0.005 g/s can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS. [ABSTRACT FROM AUTHOR]

This work describes an incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of HONO and NO2 mixing ratios in ambient air. The instrument is operated in the near-ultraviolet spectral region between 361 and 388 nm. The mirror reflectivity and optical cavity transmission function were determined from the optical extinction observed when sampling air and helium. To verify the accuracy of this approach, Rayleigh scattering cross sections of nitrogen and argon were measured and found to be in quantitative agreement with literature values. The mirror reflectivity exceeded 99.98 %, at its maximum near 373 nm, resulting in an absorption path length of 6 km from a 1 m long optical cavity. The instrument precision was assessed through Allan variance analyses and showed minimum deviations of ±58 and ±210 pptv (1σ) for HONO and NO2 , respectively, at an optimum acquisition time of 5 min. Measurements of HONO and NO2 mixing ratios in laboratory-generated mixtures by IBBCEAS were compared to thermal dissociation cavity ring-down spectroscopy (TD-CRDS) data and agreed within combined experimental uncertainties. Sample ambient air data collected in Calgary are presented. [ABSTRACT FROM AUTHOR]

The cavity ringdown spectroscopy (CRDS) of the [A.sup.2][A,sup.(')]-[X.sup.2][A.sup.(') electronic transition in the near-IR was used to investigate the stable conformers, trans (T) and gauche (G) of the ethyl peroxy radical and its perdeutero analogue. The electronic origins for the T and G conformers of [C.sub.2][H.sub.5][O.sub.2] are found to be located at 7362(1) and 7592(1) [cm.sup.-1] respectively.

Abstract: A study of D2H+ ions in their lowest rotational states is presented. The ions are generated in pulsed discharge in liquid N2 cooled He/Ar/H2/D2 gas mixture. Near infrared (NIR) second overtone transitions in the 6534–6536cm−1 (1.529–1.530μm) region are used to identify the ions and determine their degree of rotational excitation. The data were obtained using NIR cavity ringdown absorption spectroscopy (NIR-CRDS). The sensitivity obtained was typically 5×10−9 cm−1. The measured second overtone transition frequencies are in very good agreement (better than 0.02cm−1) with ab initio predictions. From the Doppler broadening the kinetic temperature of ions is estimated to be (220±50) K. The absolute number density of D2H+ as a function of H2/D2 mixing ratio and time is measured. [Copyright &y& Elsevier]

A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10-9 cm-1. The rotationally resolved overtone spectrum of the OH(ν1) + CH(ν3) stretch combination band of methanol between 6510 and 6550 cm-1 has been observed for J′=0–8 and K′=0–3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion–rotation parameters for the upper state. Four K′-localized perturbations are analyzed and the pattern of residuals is discussed. [Copyright &y& Elsevier]

[Display omitted] • Q(J)-branch vibration-inversion-rotation transitions of NH 3 probed at 6.2 µm. • First experimental investigation of air-broadening for the probed transitions. • N 2 , He, Ar, and O 2 broadening coefficients measured for the probed transitions. In this experimental investigation, collision broadening effects on the Q(J)-branch vibration-inversion-rotation spectral lines of ammonia (NH 3) within the fundamental ν 4 asymmetric bending vibrational band in the 6.2 µm mid-IR region are reported. A continuous-wave external-cavity quantum cascade laser coupled with a high-sensitive cavity ring-down spectrometer was employed to selectively probe 10 transitions in high-resolution, including few inversion doublets of gaseous NH 3. Pressure-broadening coefficients, γ N H 3 - X i (X i = He, Ar, N 2, O 2, zero-air) in cm−1 atm−1, characterizing the collision interaction between NH 3 and various external perturbing gases, including helium, argon, nitrogen, oxygen, and zero-air, were determined at room temperature (296 K). Mean collision times and optical collision diameters of each collision partner were explored to gain deeper insight into the perturber-induced collision dynamics. This investigation elucidates the intricate intermolecular interactions and collision phenomena induced by various foreign perturbers with NH 3 , with potential implications for future spectroscopic and atmospheric research of this polyatomic molecule. [ABSTRACT FROM AUTHOR]

Plastic materials provide numerous benefits. However, properties such as durability and resistance to degradation that make plastic attractive for variable applications likewise foster accumulation in the environment. Fragmentation of plastics leads to the formation of potentially hazardous microplastic, of which a considerable amount derives from polystyrene. Here, we investigated the biodegradation of polystyrene by the tropical sooty mold fungus Capnodium coffeae in different experimental setups. Growth of C. coffeae was stimulated significantly when cultured in presence of plastic polymers rather than in its absence. Stable isotope tracing using 13C-enriched polystyrene particles combined with cavity ring-down spectroscopy showed that the fungus mineralized polystyrene traces. However, phospholipid fatty acid stable isotope probing indicated only marginal assimilation of polystyrene-13C by C. coffeae in liquid cultures. NMR spectroscopic analysis of residual styrene contents prior to and after incubation revealed negligible changes in concentration. Thus, this study suggests a plastiphilic life style of C. coffeae despite minor usage of plastic as a carbon source and the general capability of sooty mold fungi to stimulate polystyrene mineralization, and proposes new standards to identify and unambiguously demonstrate plastic degrading capabilities of microbes. [Display omitted] • Capnodium coffeae develops larger colonies on MP-amended semi-solid medium. • CRDS indicates slow but steady fungal 13C-PS mineralization. • PLFA stable isotope probing indicates minor PS-derived 13C-assimilation. • Generic workflow for identification of plastic biodegraders is presented. [ABSTRACT FROM AUTHOR]

We report what we believe to be the first systematic study of Doppler-free, nonlinear absorption by use of cavity ringdown spectroscopy. We have developed a variant of cavity ringdown spectroscopy for the mid-infrared region between 9 and 11 [micro]m, exploiting the intracavity power buildup that is possible with continuous-wave lasers. The infrared source consists of a continuous-wave [CO.sub.2] laser with 1-mW tunable infrared sidebands that couple into a high-finesse stable resonator. We tune the sideband frequencies to observe a saturated, Doppler-free Lamb dip in the [v.sub.7], [11.sub.1,10] [left arrow] [11.sub.2,10] rovibrational transition of ethylene ([C.sub.2][H.sub.4]). Power studies of the Lamb dip are presented to examine the intracavity effects of saturation on the Lamb-dip linewidth, the peak depth, and the broadband absorption. [C] 2000 Optical Society of America OCIS codes: 230.5750, 300.6190, 300.6320, 300.6340, 300.6420, 300.6460.