Cavity Ring-down Laser Spectroscopy Research Articles

Isotope effects accompanying δ2 H, δ18 O and δ17 O analyses of aqueous saline solutions using cavity ring-down laser spectroscopy.

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. Here we report the results of laboratory experiments aimed at quantifying isotope effects associated with direct, δ2 H, δ18 O and δ17 O 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. 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‰ (2 H), -3.5‰ (18 O) and -1.7‰ (17 O). 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. 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 17 O-excess determinations for solutions forming hydrated salts preclude the use of this parameter for interpretation purposes.

Carbon isotope composition of respired CO2 in woody stems and leafy shoots of three tree species along the growing season: physiological drivers for respiratory fractionation.

The carbon isotope composition of respired CO2 (δ13CR) and bulk organic matter (δ13CB) of various plant compartments informs about isotopic fractionation and substrate of respiratory processes, crucial to advance understanding of carbon allocation in plants. Nevertheless, its 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, oak, and cedar trees during spring and late summer. Photosynthesis, respiration, growth, and non-structural carbohydrates were measured in parallel to evaluate potential drivers for respiratory fractionation. 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.

Improving continuous-flow analysis of triple oxygen isotopes in ice cores: insights from replicate measurements

Abstract. Stable water isotope measurements from polar ice cores provide high-resolution information about past hydrologic conditions and are therefore important for understanding earth's climate system. Routine high-resolution measurements of δ18O, δD, and deuterium excess are made by continuous-flow analysis (CFA) methods that include laser spectrometers. Cavity ring-down laser spectroscopy (CRDS) allows for simultaneous measurements of all stable water isotopes, including δ17O and 17O excess (Δ17O); however, the limitations of CFA methodologies for Δ17O are not well understood. Here, we describe a measurement methodology for all stable water isotopes that uses a CFA system coupled with a CRDS instrument. We make repeated measurements of an ice-core section using this method to explore the reproducibility of CFA–CRDS measurements for Δ17O. Our data demonstrate that the CFA–CRDS method can make high-precision measurements of Δ17O (< 5 per meg at averaging times > 3000 s). We show that the variations within our CFA ice-core measurements are well matched in magnitude and timing by the variations within the discrete CRDS measurements; we find that calibration offsets generate most of the variability among the replicate datasets. When these offsets are accounted for, the precision of CFA–CRDS ice-core data for Δ17O is as good as the precision of Δ17O for continuous reference water measurements. We demonstrate that this method can detect seasonal variability in Δ17O in Greenland ice, and our work suggests that the measurement resolution of CFA–CRDS is largely defined by the melt and measurement rate. We suggest that CFA–CRDS has the potential to increase measurement resolution of δ17O and Δ17O in ice cores, but also highlight the importance of developing calibration strategies with attention to Δ17O.

Constraints for precise and accurate fluid inclusion stable isotope analysis using water-vapour saturated CRDS techniques

Hydrogen (δ2H) and oxygen (δ18O) isotopes of water extracted from speleothem fluid inclusions are important proxies used for paleoclimate reconstruction. In our study we use a cavity ring-down laser spectroscopy system for analysis and modified the approach of Affolter et al. (2014) for sample extraction. The method is based on crushing of small sub-gram speleothem samples in a heated and continuously water-vapour purged extraction line. The following points were identified:Injection of reference water shows a precision (1σ) of 0.4–0.5 ‰ for δ18O values and 1.1–1.9 ‰ for δ2H values for water amounts of 0.1–0.5 μl, which improves with increasing water amount to 0.1–0.3 ‰ and 0.2–0.7 ‰, respectively, above 1 μl. The accuracy of measurements of water injections and water-filled glass capillaries crushed in the system is better than 0.08 ‰ for δ18O and 0.3 ‰ for δ2H values. The reproducibility (1σ) based on replicate analysis of speleothem fluid inclusion samples with water amounts >0.2 μl is 0.5 ‰ for δ18O and 1.2 ‰ for δ2H values, respectively. Isotopic differences between the water vapour background of the extraction system and the fluid inclusions have no significant impact on the measured fluid inclusion isotope values if they are within 10 ‰ for δ18O and 50 ‰ for δ2H values of the background. Tests of potential adsorption effects with inclusion free spar calcite confirm that the isotope values are unaffected by adsorption for water contents of about 1 μl (fluid inclusion) water per g of carbonate or above.Fluid inclusion analysis on three different modern to late Holocene speleothems from caves in northwest Germany resulted in δ18O and δ2H values that follow the relationship as defined by the meteoric water line and that correspond to the local drip water. Yet, due to potential isotope exchange reactions for oxygen atoms, hydrogen isotope measurements are preferentially to be used for temperature reconstructions. We demonstrate this in a case study with a Romanian stalagmite, for which we reconstruct the 20th century warming with an amplitude of approximately 1 °C, with a precision for each data point of better than ±0.5 °C.

Continuous and simultaneous measurement of triple-oxygen and hydrogen isotopes of liquid and vapor during evaporation experiments.

Oxygen and hydrogen isotopes are important tools for studying the modern and past hydrological cycle. Previous evaporation experiments used episodic measurement of liquid and/or vapor or did not measure all isotopologues of water. Here, we describe an evaporation experimental system that allows all isotopologues of liquid and water vapor to be measured simultaneously and near-continuously at high precision using cavity ring-down laser spectroscopy (CRDS). Evaporating liquid is periodically sampled from a closed recirculating loop by a syringe pump that delivers a constant supply of water to the vaporizer, achieving a water vapor concentration of 20,000 ppmV H2 O (±132, 1σ). Vapor is sampled directly from the evaporation chamber. Isotope ratios are measured simultaneously with a Picarro L2140-i CRDS instrument. For liquid measurements, Allan variance analysis indicates an optimum data collection window of 34 min for oxygen isotopes and 27 min for hydrogen isotopes. During these periods, the mean standard error is ±0.0081‰ for δ17 O values, ±0.0081‰ for δ18 O values, and ±0.019‰ for δ2 H values. For the derived parameters 17 O-excess and d-excess, the standard error of the mean is 5.8 per meg and 0.07‰, respectively. For the vapor phase a 12.5 min data window for all isotopologues results in a mean standard error of ±0.012‰ for δ17 O values, ±0.011‰ for δ18 O values, and ±0.023‰ for δ2 H values. For the derived parameters, the standard error of the mean is 9.2 per meg for 17 O-excess and 0.099‰ for d-excess. These measurements result in consistently narrow 95% confidence limits for the slopes of ln(δ17 O + 1) vs ln(δ18 O + 1) and ln(δ2 H + 1) vs ln(δ18 O + 1). The experimental method permits measurement of fractionation of triple-oxygen and hydrogen isotopes of evaporating water under varying controlled conditions at high precision. Application of this method will be useful for testing theoretical models of evaporation and conducting experiments to simulate evaporation and isotopic equilibration in natural systems.

Continuous-Flow Analysis of δ17O, δ18O, and δD of H2O on an Ice Core from the South Pole

The δD and δ18O values of water are key measurements in polar ice-core research, owing to their strong and well-understood relationship with local temperature. Deuterium excess, d, the deviation from the average linear relationship between δD and δ18O, is also commonly used to provide information about the oceanic moisture sources where polar precipitation originates. Measurements of δ17O and “17O excess” (Δ17O) are also of interest because of their potential to provide information complementary to d. Such measurements are challenging because of the greater precision required, particularly for Δ17O. Here, high-precision measurements are reported for δ17O, δ18O, and δD on a new ice core from the South Pole, using a continuous-flow measurement system coupled to two cavity ring-down laser spectroscopy instruments. Replicate measurements show that at 0.5 cm resolution, external precision is ∼0.2‰ for δ17O and δ18O, and ∼1‰ for δD. For Δ17O, achieving external precision of <0.01‰ requires depth averages of ∼50 cm. The resulting ∼54,000-year record of the complete oxygen and hydrogen isotope ratios from the South Pole ice core is discussed. The time series of Δ17O variations from the South Pole shows significant millennial-scale variability, and is correlated with the logarithmic formulation of deuterium excess (dln), but not the traditional linear formulation (d).

High-precision measurements of δ2H, δ18O and δ17O in water with the aid of cavity ring-down laser spectroscopy

ABSTRACTA thorough evaluation of measurement uncertainty together with control of short-term and long-term precision of measurements should be a basis of any successful quality assurance/quality control (QA/QC) strategy aimed at maintaining a high quality of the analytical process. Here we present the results of a comprehensive assessment of the analytical performance of a Picarro L2140-i CRDS laser spectrometer analysing δ2H, δ18O and δ17O in water. The assessment is based on results obtained during 15 months of continuous operation of this instrument (February 2017 to May 2018). The short-term precision of measured and derived quantities was 0.11, 0.036, 0.028, 0.23 ‰ and 11 per meg, for δ2H, δ18O, δ17O, d-excess and Δ17O, respectively, and is comparable to the precision reported by the manufacturer. The long-term precision of the L2140-i, defined as standard uncertainty of the time series of 153 analyses of a laboratory standard conducted throughout 15 months, was roughly two times lower (0.24, 0.053, 0.038, 0.37 ‰ and 21 per meg, for δ2H, δ18O, δ17O, d-excess and Δ17O). In-depth assessment of the measurement uncertainty of a single analysis revealed that assigned uncertainty of the calibration standards is an important component of the uncertainty budget, especially in case of δ2H analysis.

Isotope ratio laser spectroscopy to disentangle xylem-transported from locally respired CO2 in stem CO2 efflux

Respired CO2 in woody tissues radially diffuses to the atmosphere or it is transported upward with the transpiration stream, making the origin of CO2 in stem CO2 efflux (EA) uncertain, which may confound stem respiration (RS) estimates. An aqueous 13C-enriched solution was infused into stems of Populus tremula L. trees, and real-time measurements of 13C-CO2 and 12C-CO2 in EA were performed via Cavity Ring Down Laser Spectroscopy (CRDS). The contribution of locally respired CO2 (LCO2) and xylem-transported CO2 (TCO2) to EA was estimated from their different isotopic composition. Mean daily values of TCO2/EA ranged from 13% to 38%, evidencing the notable role that xylem CO2 transport plays in the assessment of stem respiration. Mean daily TCO2/EA did not differ between treatments of drought stress and light exclusion of woody tissues, but they showed different TCO2/EA dynamics on a sub-daily time scale. Sub-daily CO2 diffusion patterns were explained by a light-induced axial CO2 gradient ascribed to woody tissue photosynthesis, and the resistance to radial CO2 diffusion determined by bark water content. Here, we demonstrate the outstanding potential of CRDS paired with 13C-CO2 labelling to advance in the understanding of CO2 movement at the plant-atmosphere interface and the respiratory physiology in woody tissues.

Triple oxygen isotope analysis of nitrate using isotope exchange cavity ringdown laser spectroscopy.

Triple oxygen isotopes (16 O/17 O/18 O) in nitrate are a valuable tool to ascertain the pathways of nitrate formation in the atmosphere and the fate of nitrate in ecosystems. Here we present a new method for determining Δ17 O values in nitrates, based on nitrate-water isotope equilibration (IE) and subsequent isotopic analysis of water using cavity ringdown laser spectroscopy (CRDS). Nitrate oxygen (O-NO3 - ) is equilibrated with water oxygen (O-H2 O) at low pH and 80°C. Subsequently, the δ17 O and δ18 O values of equilibrated water are determined by CRDS, scaled to V-SMOW and V-SLAP and calibrated against nitrate standards (USGS-34, USGS-35 and IAEA-NO3). We provide isotopic measurements of synthetic and natural nitrates and a direct inter-lab comparison with the classic method of thermal-decomposition of nitrate followed by isotope ratio mass spectrometry of O2 (TD-IRMS). For synthetic NaNO3 , the precision (1SD) of the IE-CRDS method is 0.8‰ for δ17 O values, 1.7‰ for δ18 O values and 0.2‰ for Δ17 O values when using an O-NO3 - /O-H2 O ratio greater than 0.0114±0.0001 (e.g. 12μmol of NO3 - in 50μL of acid solution). For natural samples, after purification of nitrates by column chemistry and reprecipitation as AgNO3 , the precision is better than 1.8‰ for δ17 O values, 3.2‰ for δ18 O values and 1‰ for Δ17 O values. IE-CRDS and TD-IRMS yield Δ17 O values within the analytical errors of the two methods. The IE-CRDS method for determining Δ17 O values in nitrates utilizes a user-friendly and relatively cheaper benchtop analytical instrument, representing an alternative to IRMS-based methods for certain applications.

Use of IR Absorption Laser Spectroscopy at Nuclear Fuel Cycle Plants: Problems and Prospects (Review)

The main stages of the nuclear fuel cycle from extraction of uranium ores to disposal of radioactive waste resulting from the processing of spent nuclear fuel were briefly analyzed. A list of the most probable radioactive substances and toxic chemicals that can be part of emergency emissions at each stage of the nuclear fuel cycle was composed. The basic physical principles of local and remote IR absorption laser technologies for detecting radioactive substances and toxic chemicals in the atmosphere for solving some unique problems of environmental monitoring were considered. The analytical potential of the currently most effective laser technologies for atmospheric monitoring at nuclear fuel cycle plants based on the achievements of diode laser spectroscopy, cavity ringdown laser spectroscopy, and optoacoustic laser spectroscopy using diode and quantum-cascade lasers was discussed. Current trends in the development of laser technologies for atmospheric monitoring in different IR spectral ranges were analyzed.

Nuclear spin symmetry conservation and relaxation of water (H216O) seeded in supersonic jets of argon and oxygen: measurements by cavity ring-down laser spectroscopy

ABSTRACTWe have investigated nuclear spin symmetry conservation and relaxation of water seeded in argon or molecular oxygen using supersonic jet expansions probed by high-resolution continuous-wave laser cavity ring-down spectroscopy. The probing of the R-branch of the 2 band (above 7500 cm1) was used to complement our previous investigation. We were able to further cool down the water samples (down to 17 K., i.e. 7 K colder than before) and double the data set (regarding argon as carrier gas). We confirm our first observations: at the lowest rotational temperatures and low partial pressures of HO, nuclear spin symmetry is conserved, in agreement with theoretical expectation for inelastic collisions. For high concentrations of water in the gas mixture, we obtained higher rotational temperatures and were able to observe nuclear spin symmetry relaxation. This can be related to the formation of water clusters at the early stage of the supersonic jet expansion. We also present the analogous series of measurements performed using molecular oxygen (O) as carrier gas: we observed similar behaviour for low and high concentrations of water in the gas mixtures when cooling the samples to 16 K. The conservation of nuclear spin symmetry at low temperature and low concentration using oxygen as carrier gas indicates that the paramagnetic collisional partner does not play a significant role regarding the possible nuclear spin symmetry conversion of water. We discuss possible mechanisms related to our observations of apparent nuclear spin symmetry relaxation.

Online Differential Thermal Isotope Analysis of Hydration Water in Minerals by Cavity Ringdown Laser Spectroscopy.

We have developed a new method for measuring the isotopic composition (δ18O and δD) of different types of bonded water (e.g., molecular water, hydroxyl) contained in hydrated minerals by coupling a thermal gravimeter (TG) and a cavity ringdown laser spectrometer (CRDS). The method involves precisely step-heating a mineral sample, allowing the separation of the different types of waters that are released at different temperatures. Simultaneously, the water vapor evolved from the mineral sample is analyzed for oxygen and hydrogen isotopes by CRDS. Isotopic values for the separate peaks are calculated by integrating the product of the water amounts and its isotopic values, after correcting for background. We provide examples of the application of the differential thermal isotope analysis (DTIA) method to a variety of hydrous minerals and mineraloids including gypsum, clays, and amorphous silica (opal). The isotopic compositions of the total water evolved from a set of natural gypsum samples by DTIA are compared with the results of a conventional offline water extraction method followed by CRDS analysis. The results from both methods are in excellent agreement, and precisions (1σ) for δ18O (±0.12‰) and δD (±0.8‰) of the total gypsum hydration water from the DTIA method are comparable to that obtained by the offline method. A range of analytical challenges and solutions (e.g., spectroscopic interferences produced by VOCs in natural samples, isotopic exchange with structural oxygen, etc.) are discussed. The DTIA method has wide ranging applications for addressing fundamental problems across many disciplines in earth and planetary sciences, including paleoclimatology, sedimentology, volcanology, water exchange between the solid earth and hydrosphere, and water on Mars and other planetary bodies.

Evaluation of carrier gases for high-precision water isotopic measurements by cavity ring-down laser spectroscopy

ABSTRACTThe carrier gas is important for obtaining stable, precise hydrogen and oxygen isotopic ratios in water samples using cavity ring-down laser spectroscopy. The δ2H and δ18O variations were investigated using four carrier gases under two microcombustion conditions. Although most deviations of δ2H and δ18O values were within the standard deviation of the instrument, statistical analysis indicated that carrier gas provided by a drying tube with higher water background was not suitable for cavity ring-down laser spectroscopy. In addition, the microcombustion on condition did not significantly improve the precision and accuracy of δ2H and δ18O measurements. Therefore, the best method for achieving highly precise results involved the use of low water containing compressed air as the carrier gas with the microcombustion warm condition.

Simultaneous analysis of (17) O/(16) O, (18) O/(16) O and (2) H/(1) H of gypsum hydration water by cavity ring-down laser spectroscopy.

RationaleThe recent development of cavity ring‐down laser spectroscopy (CRDS) instruments capable of measuring 17O‐excess in water has created new opportunities for studying the hydrologic cycle. Here we apply this new method to studying the triple oxygen (17O/16O, 18O/16O) and hydrogen (2H/1H) isotope ratios of gypsum hydration water (GHW), which can provide information about the conditions under which the mineral formed and subsequent post‐depositional interaction with other fluids.MethodsWe developed a semi‐automated procedure for extracting GHW by slowly heating the sample to 400°C in vacuo and cryogenically trapping the evolved water. The isotopic composition (δ17O, δ18O and δ2H values) of the GHW is subsequently measured by CRDS. The extraction apparatus allows the dehydration of five samples and one standard simultaneously, thereby increasing the long‐term precision and sample throughput compared with previous methods. The apparatus is also useful for distilling brines prior to isotopic analysis. A direct comparison is made between results of 17O‐excess in GHW obtained by CRDS and fluorination followed by isotope ratio mass spectrometry (IRMS) of O2.ResultsThe long‐term analytical precision of our method of extraction and isotopic analysis of GHW by CRDS is ±0.07‰ for δ17O values, ±0.13‰ for δ18O values and ±0.49‰ for δ2H values (all ±1SD), and ±1.1‰ and ±8 per meg for the deuterium‐excess and 17O‐excess, respectively. Accurate measurement of the 17O‐excess values of GHW, of both synthetic and natural samples, requires the use of a micro‐combustion module (MCM). This accessory removes contaminants (VOCs, H2S, etc.) from the water vapour stream that interfere with the wavelengths used for spectroscopic measurement of water isotopologues. CRDS/MCM and IRMS methods yield similar isotopic results for the analysis of both synthetic and natural gypsum samples within analytical error of the two methods.ConclusionsWe demonstrate that precise and simultaneous isotopic measurements of δ17O, δ18O and δ2H values, and the derived deuterium‐excess and 17O‐excess, can be obtained from GHW and brines using a new extraction apparatus and subsequent measurement by CRDS. This method provides new opportunities for the application of water isotope tracers in hydrologic and paleoclimatologic research. © 2015 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.

Oxygen and hydrogen isotope signatures of Northeast Atlantic water masses

Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 δ18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, δD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0–100m) and central (100–500m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5‰ for δ18O and 0 to 2‰ for δD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high δ18O (0.5–1.1‰) and δD (3–6‰) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (δ18O: −0.1 to 0.5‰; δD: −1 to 4‰) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed δ18O–salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0.46 described previously by Pierre et al. (1994, J. Mar. Syst. 5 (2), 159–170.) for the tropical to subtropical Northeast Atlantic. This slope decreases to 0.46 for the subtropical North Atlantic Central Water (NACW) and the MOW and to 0.32 for the surface waters of the upper 50m. The δD–salinity mixing lines have estimated slopes of 3.01 for the complete data, 1.26 for the MOW, 3.47 for the NACW, and 2.63 for the surface waters. The slopes of the δ18O–δD relationship are significantly lower than the one for the Global Meteoric Water Line with 5.6 for the complete data set, 2.30 for the MOW, 4.79 for the NACW, and 3.99 for the surface waters. The lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics.

UV-Light-Induced Water Condensation in Air and the Role of Hydrogen Peroxide

Abstract We report the UV-light-induced formation of water aerosol/droplets in air based on laser-light scattering measurements, differential mobility analyses and cavity ring-down laser spectroscopy (CRDS), and propose a mechanism. It was shown that UV-light (185 nm) irradiation of air within a soap bubble rapidly produced water droplets under supersaturated conditions. Multiple UV irradiation cycles were demonstrated to increase particle sizes in a controlled reaction chamber. We propose that the reaction mechanism is initiated by oxygen (O2) photodissociation and ozone (O3) formation and further photodissociation of O3 leads to sequential dark reactions, generating hydrogen peroxide (H2O2) as a hygroscopic stable product. Exciting excess O3 in wet air with mid-UV radiations (254 nm) was also demonstrated to produce water particles, indicating that this series of reactions can be started at an intermediate stage using a longer wavelength of UV light. For the first time, it was demonstrated that H2O2 in air is a precursor of the initial nucleation of water with two different aerosol formation schemes at 263 K: a) from a mixture of H2O2 and water vapor in dark and b) from a mixture of O3 and water vapor by mid-UV (266 nm) light irradiation. These results indicate that H2O2 can capture water molecules and form water particles.

Challenges in measuring the δ13C of the soil surface CO2 efflux

The δ13C of the soil surface efflux of carbon dioxide (δ13CRS) has emerged as a powerful tool enabling investigation of a wide range of soil processes from characterising entire ecosystem respiration to detailed compound-specific isotope studies. δ13CRS can be used to trace assimilated carbon transfer below ground and to partition the overall surface efflux into heterotrophic and autotrophic components. Despite this wide range of applications no consensus currently exists on the most appropriate method of sampling this surface efflux of CO2 in order to measure δ13CRS. Here we consider and compare the methods which have been used, and examine the pitfalls. We also consider a number of analysis options, isotope ratio mass spectrometry (IRMS), tuneable diode laser spectroscopy (TDLS) and cavity ring-down laser spectroscopy (CRDS). δ13CRS is typically measured using chamber systems, which fall into three types: closed, open and dynamic. All are imperfect. Closed chambers often rely on Keeling plots to estimate δ13CRS, which may not be appropriate without free turbulent air mixing. Open chambers have the advantage of being able to maintain steady-state conditions but analytical errors may become limiting with low efflux rates. Dynamic chambers like open chambers are complex, and controlling pressure fluctuations caused by air movement is a key concern. Both open and dynamic chambers in conjunction with field portable TDLS and CRDS analysis systems have opened up the possibility of measuring δ13CRS in real time permitting new research opportunities and are on balance the most suited to this type of measurement.

Radioactive Carbon Isotope Monitoring System Based on Cavity Ring-down Laser Spectroscopy for Decommissioning Process of Nuclear Facilities

In decommissioning process of nuclear facilities, large amount of radioactive isotopes are discharged as waste. Radioactive carbon isotope (14C) is one of the key nuclides to determine the upper limit of concentration in the waste disposal. In particular, 14C on the graphite reactor decommissioning should be separated from stable carbon isotopes (12C and 13C) and monitored for the public health and safety. We propose an isotope analysis system based on cavity ring-down laser spectroscopy (CRDS) to monitor the carbon isotopes (12C, 13C and 14C) in the isotope separation process for the graphite reactor decommissioning. This system is compact and suitable for a continuous monitoring, because the concentration of molecules including the carbon isotope is derived from its photo absorbance with ultra high sensitive laser absorption spectroscopy. Here are presented the necessary conditions of CRDS system for 14C isotope analysis through the preliminary experimental results of 13C isotope analysis with a prototype system.

Rapid-Swept CW Cavity Ring-down Laser Spectroscopy for Carbon Isotope Analysis

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (12C16O2, 13C16O2) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm−1(1.6)mm). The isotopic ratio has been obtained as (1.07±0.13)x 10−2, in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3x 10−8cm−1.

Rapid-Swept CW Cavity Ring-down Laser Spectroscopy for Carbon Isotope Analysis

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (12C16O2, 13C16O2) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm−1(1.6)mm). The isotopic ratio has been obtained as (1.07±0.13)x 10−2, in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3x 10−8cm−1.