Water vapor δ&lt;sup&gt;2&lt;/sup&gt;H and δ&lt;sup&gt;18&lt;/sup&gt;O  measurements using off-axis integrated cavity output spectroscopy

Abstract. We 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 ink jet technology 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.

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Water vapor δ2H and δ18O measurements using off-axis integrated cavity output spectroscopy

Atmospheric Measurement Techniques ◽

10.5194/amt-3-67-2010 ◽

2010 ◽

Vol 3 (1) ◽

pp. 67-77 ◽

Cited By ~ 75

Author(s):

P. Sturm ◽

A. Knohl

Keyword(s):

Water Vapor ◽

Concentration Dependence ◽

Temperature Sensitivity ◽

Dew Point ◽

Calibration System ◽

Term Stability ◽

Long Term Stability ◽

Cavity Output ◽

Isotope Measurements

Abstract. We 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.

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A Miniaturised, Fully Integrated NDIR CO2 Sensor On-Chip

Sensors ◽

10.3390/s21165347 ◽

2021 ◽

Vol 21 (16) ◽

pp. 5347

Author(s):

Xiaoning Jia ◽

Joris Roels ◽

Roel Baets ◽

Gunther Roelkens

Keyword(s):

Water Vapor ◽

Limit Of Detection ◽

Wafer Level ◽

Water Vapor Absorption ◽

Optical Source ◽

Fully Integrated ◽

Term Stability ◽

Long Term Stability ◽

Co2 Sensor

In this paper, we present a fully integrated Non-dispersive Infrared (NDIR) CO2 sensor implemented on a silicon chip. The sensor is based on an integrating cylinder with access waveguides. A mid-IR LED is used as the optical source, and two mid-IR photodiodes are used as detectors. The fully integrated sensor is formed by wafer bonding of two silicon substrates. The fabricated sensor was evaluated by performing a CO2 concentration measurement, showing a limit of detection of ∼750 ppm. The cross-sensitivity of the sensor to water vapor was studied both experimentally and numerically. No notable water interference was observed in the experimental characterizations. Numerical simulations showed that the transmission change induced by water vapor absorption is much smaller than the detection limit of the sensor. A qualitative analysis on the long term stability of the sensor revealed that the long term stability of the sensor is subject to the temperature fluctuations in the laboratory. The use of relatively cheap LED and photodiodes bare chips, together with the wafer-level fabrication process of the sensor provides the potential for a low cost, highly miniaturized NDIR CO2 sensor.

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The stability and calibration of water vapor isotope ratio measurements during long-term deployments

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-5425-2015 ◽

2015 ◽

Vol 8 (5) ◽

pp. 5425-5466 ◽

Cited By ~ 5

Author(s):

A. Bailey ◽

D. Noone ◽

M. Berkelhammer ◽

H. C. Steen-Larsen ◽

P. Sato

Keyword(s):

Water Vapor ◽

Concentration Dependence ◽

Hydrological Cycle ◽

Dew Point ◽

Vapor Concentration ◽

Mauna Loa ◽

Laser Absorption ◽

Low Humidity ◽

The Stability

Abstract. With the recent advent of commercial laser absorption spectrometers, field studies measuring stable isotope ratios of hydrogen and oxygen in water vapor have proliferated. These pioneering analyses have provided invaluable feedback about best strategies for optimizing instrumental accuracy, yet questions still remain about instrument performance and calibration approaches for multi-year field deployments. With clear scientific potential for using these instruments to carry out long-term monitoring of the hydrological cycle, this study examines the long-term stability of the isotopic biases associated with three cavity-enhanced laser absorption spectrometers – calibrated with different systems and approaches – at two remote field sites: Mauna Loa Observatory, Hawaii, USA, and Greenland Environmental Observatory, Summit, Greenland. The analysis pays particular attention to the stability of measurement dependencies on water vapor concentration and also evaluates whether these so-called concentration-dependences are sensitive to statistical curve-fitting choices or measurement hysteresis. The results suggest evidence of monthly-to-seasonal concentration-dependence variability – which likely stems from low signal-to-noise at the humidity-range extremes – but no long-term directional drift. At Mauna Loa, where the isotopic analyzer is calibrated by injection of liquid water standards into a vaporizer, the largest source of inaccuracy in characterizing the concentration-dependence stems from an insufficient density of calibration points at low humidity. In comparison, at Greenland, the largest source of inaccuracy is measurement hysteresis associated with interactions between the reference vapor, generated by a custom dew point generator (DPG), and the sample tubing. Nevertheless, prediction errors associated with correcting the concentration-dependence are small compared to total measurement uncertainty. At both sites, a dominant source of uncertainty is instrumental precision at low humidity, which cannot be reduced by improving calibration strategies. Challenges in monitoring long-term isotopic drift are also discussed in light of the different calibration systems evaluated.

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Evaluation of the Long-Term Stability and Temperature Coefficient of Dew-Point Hygrometers

International Journal of Thermophysics ◽

10.1007/s10765-012-1346-2 ◽

2012 ◽

Vol 33 (8-9) ◽

pp. 1758-1770

Author(s):

R. Benyon ◽

T. Vicente ◽

P. Hernández ◽

L. De Rivas ◽

F. Conde

Keyword(s):

Temperature Coefficient ◽

Dew Point ◽

Term Stability ◽

Long Term Stability

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The stability and calibration of water vapor isotope ratio measurements during long-term deployments

Atmospheric Measurement Techniques ◽

10.5194/amt-8-4521-2015 ◽

2015 ◽

Vol 8 (10) ◽

pp. 4521-4538 ◽

Cited By ~ 23

Author(s):

A. Bailey ◽

D. Noone ◽

M. Berkelhammer ◽

H. C. Steen-Larsen ◽

P. Sato

Keyword(s):

Water Vapor ◽

Concentration Dependence ◽

Hydrological Cycle ◽

Dew Point ◽

Vapor Concentration ◽

Prediction Errors ◽

Mauna Loa ◽

Laser Absorption ◽

The Stability

Abstract. With the recent advent of commercial laser absorption spectrometers, field studies measuring stable isotope ratios of hydrogen and oxygen in water vapor have proliferated. These pioneering analyses have provided invaluable feedback about best strategies for optimizing instrumental accuracy, yet questions still remain about instrument performance and calibration approaches for multi-year field deployments. With clear scientific potential for using these instruments to carry out monitoring of the hydrological cycle, this study examines the long-term stability of the isotopic biases associated with three cavity-enhanced laser absorption spectrometers – calibrated with different systems and approaches – at two remote field sites: Mauna Loa Observatory, Hawaii, USA, and Greenland Environmental Observatory, Summit, Greenland. The analysis pays particular attention to the stability of measurement dependencies on water vapor concentration and also evaluates whether these so-called concentration dependences are sensitive to statistical curve-fitting choices or measurement hysteresis. The results suggest evidence of monthly-to-seasonal concentration-dependence variability – which likely stems from low signal-to-noise at the humidity-range extremes – but no long-term directional drift. At Mauna Loa, where the isotopic analyzer is calibrated by injection of liquid water standards into a vaporizer, the largest source of inaccuracy in characterizing the concentration dependence stems from an insufficient density of calibration points at low water vapor volume mixing ratios. In comparison, at Summit, the largest source of inaccuracy is measurement hysteresis associated with interactions between the reference vapor, generated by a custom dew point generator, and the sample tubing. Nevertheless, prediction errors associated with correcting the concentration dependence are small compared to total measurement uncertainty. At both sites, changes in measurement repeatability that are not predicted by long-term linear drift estimates are a larger source of error, highlighting the importance of measuring isotopic standards with minimal or well characterized drift at regular intervals. Challenges in monitoring isotopic drift are discussed in light of the different calibration systems evaluated.

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