Exploration of unconventional natural gas reservoirs such as impermeable shale basins through the use ofhorizontal drilling and hydraulic fracturing has changed the energy landscape in the USA providing a vastnew energy source. The accelerated production of natural gas has triggered a debate concerning thesafety and possible environmental impacts of these operations. This study investigates…

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…

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…

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.…

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…

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…

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…

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…

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…

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. The analyzer can measure H…

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…

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…

Horizontal drilling and hydraulic fracturing are transforming energy production, but their potential environmental effects remain controversial. We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of…

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…

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 ^18…

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…

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. Based on methane and oxygen distributions measured at 207 stations throughout the affected region, we find that within…

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…