1,721,316 research outputs found
Kohlendioxid-, Wasserdampf- und Waermeaustausch eines durch Windwurf gestoerten Waldoekosystems in der west-russischen Taiga
No full textWater 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
Eddy covariance measurements of the dual-isotope composition of evapotranspiration
No full textMeasurements of the isotopic composition of water vapor (H2O) provide valuable insights into the hydrological cycle, whereas eddy covariance (EC) measurements are widely used to quantify biosphere-atmosphere exchange processes. Yet, the direct combination of water isotope approaches and the EC method remains technically challenging. Here, we present the first EC measurements of δ18O and δD of evapotranspiration (ET) over the full growing season of a beech forest in central Germany. This EC implementation is based on 2 Hz measurements of the mole fraction and isotopic composition of water vapor (CH2O,v, δD and δ18O) with a customized version of a commercially available water vapor isotope analyzer. The isotopic composition of ET showed a seasonal variability from −19 to 0‰ for δ18OET and from −140 to −25‰ for δDET. The setup-specific limitations of our measurements yield a mean bias of 0.03 mmol m−2 s−1 of the measured net water flux. Spectral and cospectral analysis showed that high-frequency dampening was less pronounced for our EC setup (which was equipped with heated tubing) than for the standard EC setup at this site. Thus, we conclude that direct EC measurements of the isotopic composition of ET are feasible for both, δ18OET and δDET. We propose that EC-based measurements of the isotopic composition of ET are feasible to improve our understanding of the hydrological cycle, especially where flux gradient methods show limited applicability. Our simultaneous measurements of δDET and δ18OET reveal the difference between transpiration-dominated and evaporation-dominated periods. This study highlights the potential of simultaneous measurements of δ18OET and δDET
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