Cavity ring-down spectroscopy (CRDS) is a new and evolving technology that shows great promise for isotopic δ(18)O and δ(2)H analyses of pore water from equilibrated headspace H(2)O vapor from environmental and geologic cores. We show that naturally occurring levels of CH(4) can seriously interfere with CRDS spectra, leading to erroneous δ(18)O and δ(2)H results for water. We created a new CRDS correction algorithm to account for CH(4) concentrations typically observed in subsurface and anaerobic environments, such as ground waters or lake bottom sediments.

We used metabolic tracers and modeling to analyze the response of soil metabolism to a sudden temperature change from 4 to 20 °C. We hypothesized that intact soil microbial communities would exhibit shifts in pentose phosphate pathway and glycolysis activity as observed for individual microorganisms in pure culture, and that increased maintenance respiration at higher temperature would result in greater energy production and reduced carbon use efficiency (CUE). Two hours after temperature increase, respiration increased almost 10-fold.

For anchoring CO2 isotopic measurements on the δ18OVPD-CO2 scale, the primary reference material (NBS 19 calcite) needs to be digested using concentrated ortho-phosphoric acid. During this procedure, great care must be taken to ensure that the isotopic composition of the liberated gas is accurate. Apart from controlling the reaction temperature to ±0.1°C, the potential for oxygen isotope exchange between the produced CO2 and water must be kept to a minimum. The water is usually assumed to reside on the walls in the headspace of the reaction vessel.

In order to study controls on metabolic processes in soils, we determined the dynamics of ¹³CO₂ production from two position-specific ¹³C-labeled pyruvate isotopologues in the presence and absence of glucose, succinate, pine, and legume leaf litter, and under anaerobic conditions. We also compared ¹³CO₂ production in soils along a semiarid substrate age gradient in Arizona.

Presentation Description:

The NOAA ESRL GMD Carbon Cycle and Greenhouse Gases Group’s aircraft network consists of 18 sites, mostly in North America, that conduct bi-weekly flask sampling over given locations to altitudes of 8000 m above sea level (masl). Most sites sample 12 flasks during an altitude profile, and through collaboration with GMD’s Ozone group, many conduct continuous ozone measurements as well. In March 2009, a new site in Alaska (site code ACG) was added to our network, through a collaborative effort with the U.S. Coast Guard (USCG).

A portable stable carbon isotope ratio analyzer for carbon dioxide, based on wavelength scanned cavity ringdown spectroscopy, has been used to detect, locate, and characterize an intentional leakage of CO₂ from an underground pipeline at the ZERT experimental facility in Bozeman, Montana. Rapid (1 h) walking surveys of the 100 m x 100 m site surrounding the pipeline were collected using this mobile, real-time instrument.

Monitoring is essential for the approval and control of geological storage of carbon dioxide and to judge the effectiveness of the technology in mitigating CO₂ emissions and climate change. We present a strategy for monitoring the atmosphere in the vicinity of a geological storage project that is designed to detect and quantify potential emissions. The strategy includes measurements of CO₂, CO₂ fluxes and tracers, combined with model simulations of atmospheric dispersion and ecosystem CO₂ fluxes.

Direct quantification of fossil fuel CO₂ (CO₂ff) in atmospheric samples can be used to examine several carbon cycle and air quality questions. We collected in situ CO₂, CO, and CH₄ measurements and flask samples in the boundary layer and free troposphere over Sacramento, California, USA, during two aircraft flights over and downwind of this urban area during spring of 2009. The flask samples were analyzed for Δ¹⁴CO₂ and CO₂ to determine the recently added CO₂ff mole fraction.

We investigated the moisture origin and contribution of different water sources to surface runoff entering the headwaters of the Heihe River basin on the basis of NECP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) re-analysis data and variations in the stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) of precipitation, spring, river, and melt water.

The hydrogen and oxygen isotope ratios of water vapor can be measured with commercially available laser spectroscopy analyzers in real time. Operation of the laser systems in relatively dry air is difficult because measurements are non-linear as a function of humidity at low water concentrations. Here we use field-based sampling coupled with traditional mass spectrometry techniques for assessing linearity and calibrating laser spectroscopy systems at low water vapor concentrations.

Bats are one of the most successful mammalian groups, even though their foraging activities are restricted to the hours of twilight and night-time. Some studies suggested that bats became nocturnal because of overheating when flying in daylight. This is because—in contrast to feathered wings of birds—dark and naked wing membranes of bats efficiently absorb short-wave solar radiation. We hypothesized that bats face elevated flight costs during daylight flights, since we expected them to alter wing-beat kinematics to reduce heat load by solar radiation.

Methane was the most abundant hydrocarbon released during the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. Beyond relevancy to this anthropogenic event, this methane release simulates a rapid and relatively short-term natural release from hydrates into deepwater.

A new technique for high-resolution simultaneous isotopic analysis of δ¹⁸O and δD in liquid water is presented. A continuous stream flash evaporator has been designed that is able to vapourise a stream of liquid water in a continuous mode and deliver a stable and finely controlled water vapour sample to a commercially available infrared cavity ring-down spectrometer.

The doubly labeled water method provides an objective and accurate measure of total energy expenditure in free-living subjects and is considered the gold-standard method for this measurement. Its use, however, is limited by the need to employ isotope ratio mass spectrometry (IRMS) to obtain the high-precision isotopic abundance analyses needed to optimize the dose of expensive ¹⁸O-labeled water. Recently, cavity-ring down spectroscopy (CRDS) instruments have become commercially available and may serve as a less expensive alternative to IRMS.

The Deepwater Horizon oil spill was unprecedented in total loading of petroleum hydrocarbons accidentally released to a marine ecosystem. Controversial application of chemical dispersants presumably accelerated microbial consumption of oil components, especially in warm Gulf of Mexico surface waters. We employed δ¹³C as a tracer of oil-derived carbon to resolve two periods of isotopic carbon depletion in two plankton size classes.

Hydrogen (δ₂H) and oxygen (δ¹⁸O) stable isotope analysis is useful when tracing the origin of water in beverages, but traditional analytical techniques are limited to pure or extracted waters. We measured the isotopic composition of extracted beverage water using both isotope ratio infrared spectroscopy (IRIS; specifically, wavelength-scanned cavity ring-down spectroscopy) and isotope ratio mass spectrometry (IRMS). We also analyzed beer, sodas, juices, and milk ‘as is’ using IRIS.

Direct quantification of fossil fuel CO2(CO2ff) in atmospheric samples can be used toexamine several carbon cycle and air quality questions. We collected in-situ CO2, CO,and CH4 measurements and flask samples in the boundary layer and free troposphere5 over Sacramento, California, USA, during two aircraft flights over and downwind ofthis urban area during spring of 2009. The flask samples were analyzed for ∆14CO2and CO2to determine the recently added CO2ff mole fraction. A suite of additionalgreenhouse gases including hydrocarbons and halocarbons were measured in thesame samples.

To monitor the continental carbon cycle, a fullyautomated low maintenance measurement system is installedat the Zotino Tall Tower Observatory in Central Siberia(ZOTTO, 60◦480N, 89◦210E) since April 2009. A cavity ring-down spectroscopy (CRDS) analyzer continuouslymeasures carbon dioxide (CO2) and methane (CH4) fromsix heights up to 301 m a.g.l. Buffer volumes in each airline remove short term CO2 and CH4 mixing ratio fluctuations associated with turbulence, and allow continuous, nearconcurrent measurements from all tower levels.

High-accuracy continuous measurements of greenhouse gases (CO₂ and CH₄) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases.

A continuous-flow cavity ring-down spectroscopy (CRDS) system integrating a chromatographic separation technique, a catalytic combustor, and an isotopic¹³C/¹²C optical analyzer is described for the isotopic analysis of a mixture of organic compounds. A demonstration of its potential is made for the geochemically important class of short-chain hydrocarbons. The system proved to be linear over a 3-fold injection volume dynamic range with an average precision of 0.95‰ and 0.67‰ for ethane and propane, respectively.

This study demonstrates the application of Wavelength-Scanned Cavity Ring-Down Spectroscopy (WS-CRDS) technology which is used to measure the stable isotopic composition of water. This isotopic water analyzer incorporates an evaporator system that allows liquid water as well as water vapor to be measured with high precision.

Eleven instruments for the measurement of ambient concentrations of atmospheric ammonia gas (NH₃), based on eight different measurement methods were inter-compared above an intensively managed agricultural field in late summer 2008 in S. Scotland. To test the instruments over a wide range of concentrations, the field was fertilised with urea midway through the experiment, leading to an increase in the average concentration from 10 to 100 ppbv.

Researchers investigating global climate change need measurements of greenhouse gases with extreme precision and accuracy to enable the development and benchmarking of better climate models. Existing atmospheric monitors based on non-dispersive infrared (NDIR) sensors have known problems – they are non-linear, sensitive to water vapor concentration, and susceptible to drift. Many cannot easily be simultaneously calibrated across different sites to the level of accuracy required for use in atmospheric studies.

Recent measurements of carbon isotopes in carbon dioxide using near-infrared, diode-laser-based cavity ring-down spectroscopy (CRDS) are presented. The CRDS system achieved good precision, often better than 0.2‰, for 4% CO₂ concentrations, and also achieved 0.15–0.25‰ precision in a 78 min measurement time with cryotrap-based pre-concentration of ambient CO₂ concentrations (360 ppmv). These results were obtained with a CRDS system possessing a data rate of 40 ring-downs per second and a loss measurement of 4.0?×?10 -11  cm -1  Hz -1/2 .

We describe the application of cavity ring-down spectroscopy (CRDS) to the detection of trace levels of ethylene in ambient air in a cold storage room of a fruit packing facility over a several month period. We compare these results with those obtained using gas chromatography (GC), the current gold standard for trace ethylene measurements in post-harvest applications. The CRDS instrument provided real-time feedback to the facility, to optimize the types of fruit stored together, and the amount of room ventilation needed to maintain sub-10 ppb ethylene levels for kiwi fruit storage.

An historical overview of laser-based, spectroscopic methods that employ high-finesse optical resonators is presented. The overview begins with the early work in atomic absorption (1962) and optical cavities (1974) that led to the first mirror reflectivity measurements in 1980. This paper concludes with very recent extensions of cavity-enhanced methods for the study of condensed-phase media and biological systems. Methods described here include cavity ring-down spectroscopy, integrated cavity output spectroscopy, and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy.

High fluences inside cavity ring-down spectroscopy optical resonators lend themselves to fluorescence or Raman spectroscopy. An instrument at 488 nm was developed to measure extinction, and fluorescence of aerosols. A detection limit of 6 x 10^-9 cm^-1Hz^-1/2 (0.6 Mm^-1Hz^-1/2) was achieved. The fluorescence spectral power collected from a single fluorescent microsphere was 10 to 20 pW/nm. This power is sufficient to obtain the spectrum of a single microsphere with a resolution of 10 nm and signal-to-noise ratio of ~10.

Cavity enhanced spectroscopy (CES) methodology provides a much higher degree of sensitivity than that available from conventional absorption spectrometers. The aim of this chapter is to present the fundamentals of the method, and the various modifications and extensions that have been developed. In order to set the stage, the limitations of traditional absorption spectrometers are first discussed, followed by a description of cavity ring-down spectroscopy (CRDS), the most popular CES embodiment. A few other well-known CES approaches are also described in detail.

A novel instrument, based on cavity-ringdown spectroscopy (CRDS), has been developed for trace gas detection. The new instrument utilizes a widely tunable optical parametric oscillator (OPO), which incorporates a zinc–germanium–phosphide (ZGP) crystal that is pumped at 2.8 μm by a 25-Hz Er,Cr:YSGG laser. The resultant mid-IR beam profile is nearly Gaussian, with energies exceeding 200 μJ/pulse between 6 and 8 μm, corresponding to a quantum conversion efficiency of approximately 35%.

The use of isotope ratio infrared spectroscopy (IRIS) for the stable hydrogen and oxygen isotopeanalysis of water is increasing. While IRIS has many advantages over traditional isotope ratio massspectrometry (IRMS), it may also be prone to errors that do not impact upon IRMS analyses. Ofparticular concern is the potential for contaminants in the water sample to interfere with thespectroscopy, thus leading to erroneous stable isotope data. Water extracted from plant and soilsamples may often contain organic contaminants.

The quantification of greenhouse gas emissions requireshigh precision measurements made with high spatial resolution.Here we describe measurements of carbon dioxide (CO2)and methane(CH4) conducted using Purdue University’s AirborneLaboratory for Atmospheric Research (ALAR), aimed at thequantification of the “footprints” for these greenhouse gasesfor Indianapolis, IN. A cavity ring-down spectrometer measuredatmospheric concentrations, and flask samples were obtainedat various points for comparison.