1,721,063 research outputs found
Water vapor 2H and 18O measurements using off-axis integrated cavity output spectroscopy
No full textWe present a detailed assessment of a commercially available water vapor isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ measurements of 2H and 18O in water vapor. This method, based on off-axis integrated cavity output spectroscopy, 5 is an alternative to the conventional water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the analyzer in terms of precision, memory effects, concentration dependence, temperature sensitivity and long-term stability. A calibration system based on ink jet technology is used to characterize the performance and to calibrate the analyzer. Our results show that the precision at an averaging 10 time of 15 s is 0.16‰ for 2H and 0.08‰ for 18O. The isotope ratios are strongly dependent on the water mixing ratio of the air. Taking into account this concentration dependence as well as the temperature sensitivity of the instrument we obtained a long-term stability of the water isotope measurements of 0.38‰ for 2H and 0.25‰ for 18O. The accuracy of the WVIA was further assessed by comparative measure15 ments using IRMS and a dew point generator indicating a linear response in isotopic composition and H2O concentrations. The WVIA combined with a calibration system provides accurate high resolution water vapor isotope measurements and opens new possibilities for hydrological and ecological applications
Water vapor delta H-2 and delta O-18 measurements using off-axis integrated cavity output spectroscopy
No full textWe present a detailed assessment of a commercially available water vapor isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ measurements of delta H-2 and delta O-18 in water vapor. This method, based on off-axis integrated cavity output spectroscopy, is an alternative to the conventional water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the analyzer in terms of precision, memory effects, concentration dependence, temperature sensitivity and long-term stability. A calibration system based on a droplet generator is used to characterize the performance and to calibrate the analyzer. Our results show that the precision at an averaging time of 15 s is 0.16 parts per thousand for delta H-2 and 0.08 parts per thousand for delta O-18. The isotope ratios are strongly dependent on the water mixing ratio of the air. Taking into account this concentration dependence as well as the temperature sensitivity of the instrument we obtained a long-term stability of the water isotope measurements of 0.38 parts per thousand for delta H-2 and 0.25 parts per thousand for delta O-18. The accuracy of the WVIA was further assessed by comparative measurements using IRMS and a dew point generator indicating a linear response in isotopic composition and H2O concentrations. The WVIA combined with a calibration system provides accurate high resolution water vapor isotope measurements and opens new possibilities for hydrological and ecological applications.EC [MEXT-CT-2006-042268
Water vapor delta H-2 and delta O-18 measurements using off-axis integrated cavity output spectroscopy
No full textWe present a detailed assessment of a commercially available water vapor isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ measurements of delta H-2 and delta O-18 in water vapor. This method, based on off-axis integrated cavity output spectroscopy, is an alternative to the conventional water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the analyzer in terms of precision, memory effects, concentration dependence, temperature sensitivity and long-term stability. A calibration system based on a droplet generator is used to characterize the performance and to calibrate the analyzer. Our results show that the precision at an averaging time of 15 s is 0.16 parts per thousand for delta H-2 and 0.08 parts per thousand for delta O-18. The isotope ratios are strongly dependent on the water mixing ratio of the air. Taking into account this concentration dependence as well as the temperature sensitivity of the instrument we obtained a long-term stability of the water isotope measurements of 0.38 parts per thousand for delta H-2 and 0.25 parts per thousand for delta O-18. The accuracy of the WVIA was further assessed by comparative measurements using IRMS and a dew point generator indicating a linear response in isotopic composition and H2O concentrations. The WVIA combined with a calibration system provides accurate high resolution water vapor isotope measurements and opens new possibilities for hydrological and ecological applications.EC [MEXT-CT-2006-042268
Water vapor 2H and 18O measurements using off-axis integrated cavity output spectroscopy
No full textWe present a detailed assessment of a commercially available water vapor isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ measurements of 2H and 18O in water vapor. This method, based on off-axis integrated cavity output spectroscopy, 5 is an alternative to the conventional water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the analyzer in terms of precision, memory effects, concentration dependence, temperature sensitivity and long-term stability. A calibration system based on ink jet technology is used to characterize the performance and to calibrate the analyzer. Our results show that the precision at an averaging 10 time of 15 s is 0.16‰ for 2H and 0.08‰ for 18O. The isotope ratios are strongly dependent on the water mixing ratio of the air. Taking into account this concentration dependence as well as the temperature sensitivity of the instrument we obtained a long-term stability of the water isotope measurements of 0.38‰ for 2H and 0.25‰ for 18O. The accuracy of the WVIA was further assessed by comparative measure15 ments using IRMS and a dew point generator indicating a linear response in isotopic composition and H2O concentrations. The WVIA combined with a calibration system provides accurate high resolution water vapor isotope measurements and opens new possibilities for hydrological and ecological applications
Water vapor δ<sup>2</sup>H and δ<sup>18</sup>O measurements using off-axis integrated cavity output spectroscopy
No full textWe present a detailed assessment of a commercially available water vapor
isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ
measurements of δ2H and δ18O in water vapor. This method, based on off-axis
integrated cavity output spectroscopy, is an alternative to the conventional
water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the
analyzer in terms of precision, memory effects, concentration dependence,
temperature sensitivity and long-term stability. A calibration system based
on a droplet generator is used to characterize the performance and to
calibrate the analyzer. Our results show that the precision at an averaging
time of 15 s is 0.16‰ for δ2H and 0.08‰ for δ18O. The isotope
ratios are strongly dependent on the water mixing ratio of the air. Taking
into account this concentration dependence as well as the temperature
sensitivity of the instrument we obtained a long-term stability of the water
isotope measurements of 0.38‰ for δ2H and 0.25‰ for δ18O. The
accuracy of the WVIA was further assessed by comparative measurements using
IRMS and a dew point generator indicating a linear response in isotopic
composition and H2O concentrations. The WVIA combined with a calibration
system provides accurate high resolution water vapor isotope measurements and
opens new possibilities for hydrological and ecological applications
Atmospheric oxygen and associated tracers from flask sampling and continuous measurements: Tools for studying the global carbon cycle
No full textAtmospheric oxygen measurements, together with carbon dioxide, are a useful tool to deduce and disentangle carbon fluxes due to surface exchange and atmospheric transport processes. This thesis presents measurements of atmospheric oxygen and associated tracers and discusses experimental artifacts that have to be considered for high precision O2 measurements. Different analysis techniques for O2 measurements have been established and tested. Within the European project AEROCARB flask samples of atmospheric air from the high-altitude site Jungfraujoch, Switzerland, the mountain site Puy de Dôme, France, as well as from aircraft-based vertical profiling at Griffin Forest, UK, were analyzed for O2/N2, CO2 and δ13C by isotope ratio mass spectrometry.
The four-year records of Jungfraujoch and the three-year records of Puy de Dôme show distinct seasonal cycles and superimposed long-term trends in the measured parameters. At Jungfraujoch the seasonal variations are about two times smaller than at Puy de Dôme. The
seasonal O2:CO2 correlation gives at both sites slopes of about 2 mol O2/mol CO2. Stable carbon isotope ratios of source CO2 showed depleted values in wintertime and isotopically enriched values in summer.
At the Griffin Forest site, the peak-to-peak amplitude of the seasonal cycle of O2/N2 decreases from 171 per meg at 800 m to 113 per meg at 3100 m. Furthermore the seasonal cycle is shifted from low to high altitudes with a lag of about 1 month. The same features are observed for CO2 with a decrease in the peak-to-peak amplitude of the seasonal cycle from 17.6 ppm at 800 m to 11.4 ppm at 3100 m. The vertical profiles show decreasing O2/N2 ratios in summer and increasing O2/N2 ratios in wintertime with increasing sampling height, due to surface exchange of oxygen with the land biosphere. The O2:CO2 exchange ratio for selected vertical profiles varies between −1.5 and −2.4 mol O2/mol CO2.
Technical aspects of the mass spectrometric method and gas handling procedures played a key role in achieving the required precision for O2 measurements. In particular, glass flask storage drift due to permeation of atmospheric gases through polymer seals proved to be a crucial issue for δO2/N2 flask sampling programs.
Continuous observations of CO2, 222Rn, O2/N2, and stable isotopes of CO2 at Bern, Switzerland, shed light on diurnal and seasonal patterns of the carbon cycle in an urban atmosphere. There is considerable variance in nighttime δ13C and δ18O of source CO2 throughout the year, however, with generally lower values in winter compared to summertime. The O2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between −0.96 and −1.54. Concurrent Ar/N2 measurements showed again the importance of artifacts like thermal fractionation for precise measurements of O2/N2. Using the correlation from short term fluctuations of CO2 and 222Rn we estimated a mean CO2 flux density between February 2004 and April 2004 in the region of Bern of 95 ± 39 tC km−2 month−1.
Additionally, analyzer systems for continuous O2 and CO2 measurements were developed. In the framework of the European CarboEurope-IP project O2 and CO2 will be measured continuously at Jungfraujoch. Atmospheric O2 is measured by paramagnetic as well as fuel cell techniques. A second O2 and CO2 analyzer system dedicated for making measurements during long distance flights in a passenger aircraft was developed in the context of the European CARIBIC project. Our instrument is based on electrochemical cells for O2 analysis and a NDIR analyzer for CO2 measurements.
In summary, this thesis contributes to the observational database for atmospheric O2 and CO2 measurements and reveals important technical issues for accurate measurements of atmospheric composition
Soil matrix tracer contamination and canopy recycling did not impair<sup>13</sup>CO<sub>2</sub>plant–soil pulse labelling experiments
No full textWhen conducting 13CO2 plant–soil pulse labelling experiments, tracer material might cause unwanted side effects which potentially affect δ13C measurements of soil respiration (δ13CSR) and the subsequent data interpretation. First, when the soil matrix is not isolated from the atmosphere, contamination of the soil matrix with tracer material occurs leading to a physical back-diffusion from soil pores. Second, when using canopy chambers continuously, 13CO2 is permanently re-introduced into the atmosphere due to leaf respiration which then aids re-assimilation of tracer material by the canopy. Accordingly, two climate chamber experiments on European beech saplings (Fagus sylvatica L.) were conducted to evaluate the influence of soil matrix 13CO2 contamination and canopy recycling on soil 13CO2 efflux during 13CO2 plant–soil pulse labelling experiments. For this purpose, a combined soil/canopy chamber system was developed which separates soil and canopy compartments in order to (a) prevent diffusion of 13C tracer into the soil chamber during a 13CO2 canopy pulse labelling and (b) study stable isotope processes in soil and canopy individually and independently. In combination with laser spectrometry measuring CO2 isotopologue mixing ratios at a rate of 1 Hz, we were able to measure δ13C in canopy and soil at very high temporal resolution. For the soil matrix contamination experiment, 13CO2 was applied to bare soil, canopy only or, simultaneously, to soil and canopy of the beech trees. The obtained δ13CSR fluxes from the different treatments were then compared with respect to label re-appearance, first peak time and magnitude. By determining the δ13CSR decay of physical 13CO2 back-diffusion from bare soils (contamination), it was possible to separate biological and physical components in δ13CSR of a combined flux of both. A second pulse labelling experiment, with chambers permanently enclosing the canopy, revealed that 13CO2 recycling at canopy level had no effect on δ13CSR dynamics
Eddy covariance measurements of CO2 isotopologues with a quantum cascade laser absorption spectrometer
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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