scholarly journals Calibration of isotopologue-specific optical trace gas analysers: a practical guide

2018 ◽  
Vol 11 (11) ◽  
pp. 6189-6201 ◽  
Author(s):  
David W. T. Griffith
Keyword(s):  
Isotopic Composition ◽  
High Precision ◽  
Total Concentration ◽  
Systematic Errors ◽  
Trace Gas ◽  
Target Range ◽  
Isotopic Ratios ◽  
Spectroscopic Techniques ◽  
Practical Guide ◽  
Atmospheric Trace Gas

Abstract. The isotopic composition of atmospheric trace gases such as CO2 and CH4 provides a valuable tracer for the sources and sinks that contribute to atmospheric trace gas budgets. In the past, isotopic composition has typically been measured with high precision and accuracy by isotope ratio mass spectrometry (IRMS) offline and separately from real-time or flask-based measurements of concentrations or mole fractions. In recent years, development of infrared optical spectroscopic techniques based on laser and Fourier-transform infrared spectroscopy (FTIR) has provided high-precision measurements of the concentrations of one or more individual isotopologues of atmospheric trace gas species in continuous field and laboratory measurements, thus providing both concentration and isotopic measurements simultaneously. Several approaches have been taken to the calibration of optical isotopologue-specific analysers to derive both total trace gas amounts and isotopic ratios, converging into two different approaches: calibration via the individual isotopologues as measured by the optical device and calibration via isotope ratios, analogous to IRMS. This paper sets out a practical guide to the calculations required to perform calibrations of isotopologue-specific optical analysers, applicable to both laser and broadband FTIR spectroscopy. Equations to calculate the relevant isotopic and total concentration quantities without approximation are presented, together with worked numerical examples from actual measurements. Potential systematic errors, which may occur when all required isotopic information is not available, or is approximated, are assessed. Fortunately, in most such realistic cases, these systematic errors incurred are acceptably small and within the compatibility limits specified by the World Meteorological Organisation – Global Atmosphere Watch. Isotopologue-based and ratio-based calibration schemes are compared. Calibration based on individual isotopologues is simpler because the analysers fundamentally measure amounts of individual isotopologues, not ratios. Isotopologue calibration does not require a range of isotopic ratios in the reference standards used for the calibration, only a range of concentrations or mole fractions covering the target range. Ratio-based calibration leads to concentration dependence, which must also be characterised.

scholarly journals Calibration of isotopologue-specific optical trace gas analysers: A practical guide

2018 ◽  
Author(s):  
David W. T. Griffith
Keyword(s):  
Isotopic Composition ◽  
High Precision ◽  
Total Concentration ◽  
Isotope Ratio Mass Spectrometry ◽  
Trace Gas ◽  
Target Range ◽  
Isotopic Ratios ◽  
Spectroscopic Techniques ◽  
Practical Guide ◽  
Atmospheric Trace Gas

Abstract. The isotopic composition of atmospheric trace gases such as CO2 and CH4 provides a valuable tracer for the sources and sinks that contribute to atmospheric trace gas budgets. In the past, isotopic composition has typically been measured with high precision and accuracy by Isotope Ratio Mass Spectrometry (IRMS) offline and separately from real-time or flask-based measurements of concentrations or mole fractions. In recent years, development of infrared optical spectroscopic techniques based on laser and Fourier Transform Infrared spectroscopy has provided high precision measurements of the concentrations of one or more individual isotopologues of atmospheric trace gas species in continuous field and laboratory measurements, thus providing both concentration and isotopic measurements simultaneously. Several approaches have been taken to the calibration of optical isotopologue-specific analysers to derive both total trace gas amounts and isotopic ratios, converging into two different approaches: calibration via the individual isotopologues as measured by the optical device, and calibration via isotope ratios, analogous to IRMS. This paper sets out a practical guide to the calculations required to perform calibrations of isotopologue-specific optical analysers, applicable to both laser- or broadband FTIR-based spectrosopy. Equations to calculate the relevant isotopic and total concentration quantities without approximation are presented, together with worked numerical examples from actual measurements. Potential errors which may occur when all required isotopic information is not available, or is approximated, are assessed. Fortunately, in most such realistic cases, the errors incurred are acceptably small and within the compatibility limits specified by the World Meteorological Organisation – Global Atmosphere Watch. Isotopologue-based and ratio-based calibration schemes are compared. Calibration based on individual isotopologues is simpler because the analysers fundamentally measure amounts of individual isotopologues, not ratios. Isotopologue calibration does not require a range of isotopic ratios in the reference standards used for the calibration, only a range of concentrations or mole fractions covering the target range. Ratio-based calibration leads to concentration dependence which must also be characterised.

Mid-infrared QPM laser sources for high-precision atmospheric trace gas measurements

2008 ◽  
Author(s):  
Dirk Richter ◽  
Petter Weibring ◽  
Alan Fried ◽  
James G. Walega ◽  
Osamu Tadanaga ◽  
...  
Keyword(s):  
High Precision ◽  
Trace Gas ◽  
Mid Infrared ◽  
Laser Sources ◽  
Gas Measurements ◽  
Atmospheric Trace Gas

Changes of Ionic and Oxygen Isotopic Composition of the Snowpack at the Glacier Austre Okstindbreen, Norway, 1995

1998 ◽  
Vol 29 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Peter Raben ◽  
Wilfred H. Theakstone
Keyword(s):  
Isotopic Composition ◽  
Sea Level ◽  
Oxygen Isotopes ◽  
Oxygen Isotopic Composition ◽  
Isotopic Ratios ◽  
Vertical Variations ◽  
Oxygen Isotopic ◽  
The Difference ◽  
Liquid Precipitation ◽  
Different Altitudes

Marked vertical variations of ions and oxygen isotopes were present in the snowpack at the glacier Austre Okstindbreen during the pre-melting phase in 1995 at sites between 825 m and 1,470 m above sea level. As the first meltwater percolated from the top of the pack, ions were moved to a greater depth, but the isotopic composition remained relatively unchanged. Ions continued to move downwards through the pack during the melting phase, even when there was little surface melting and no addition of liquid precipitation. The at-a-depth correlation between ionic concentrations and isotopic ratios, strong in the pre-melting phase, weakened during melting. In August, concentrations of Na+ and Mg2+ ions in the residual pack were low and vertical variations were slight; 18O enrichment had occurred. The difference of the time at which melting of the snowpack starts at different altitudes influences the input of ions and isotopes to the underlying glacier.

scholarly journals Spectroscopic Techniques versus Pitot Tube for the Measurement of Flow Velocity in Narrow Ducts

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7349
Author(s):  
Francesco D’Amato ◽  
Silvia Viciani ◽  
Alessio Montori ◽  
Marco Barucci ◽  
Carmen Morreale ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Pitot Tube ◽  
Optical Measurements ◽  
Trace Gas ◽  
Dual Function ◽  
Spectroscopic Techniques ◽  
Gas Composition ◽  
Flow Conditions ◽  
Theoretical Simulation

In order to assess the limits and applicability of Pitot tubes for the measurement of flow velocity in narrow ducts, e.g., biomass burning plants, an optical, dual function device was implemented. This sensor, based on spectroscopic techniques, targets a trace gas, injected inside the stack either in bursts, or continuously, so performing transit time or dilution measurements. A comparison of the two optical techniques with respect to Pitot readings was carried out in different flow conditions (speed, temperature, gas composition). The results of the two optical measurements are in agreement with each other and fit quite well the theoretical simulation of the flow field, while the results of the Pitot measurements show a remarkable dependence on position and inclination of the Pitot tube with respect to the duct axis. The implications for the metrology of small combustors’ emissions are outlined.

scholarly journals In-situ observations of the isotopic composition of methane at the Cabauw tall tower site

2016 ◽  
Author(s):  
Thomas Röckmann ◽  
Simon Eyer ◽  
Carina van der Veen ◽  
Maria E. Popa ◽  
Béla Tuzson ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
High Precision ◽  
Temporal Resolution ◽  
Isotope Ratio ◽  
Mesoscale Model ◽  
Ambient Air ◽  
Model Calculations ◽  
Dual Isotope ◽  
Methane Budget

Abstract. High precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS) based technique for in-situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw experimental site for atmospheric research (CESAR) in the Netherlands and performed in-situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of +(0.05 ± 0.03) ‰ for δ13C and –(3.6 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high precision and temporal resolution dataset does not only reveal the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site, but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget, when they are performed at multiple sites that are representative for the entire European domain.

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