Isotopes in Environmental and Health Studies, Mar 1, 2006
Symmetry selective detection of the (17)O containing ozone isotopomers (16)O(16)O(17)O and (16)O(... more Symmetry selective detection of the (17)O containing ozone isotopomers (16)O(16)O(17)O and (16)O(17)O(16)O requires the unambiguous identification of absorption lines. We report high resolution tuneable diode laser spectrometer measurements of (17)O containing ozone isotopomers in the R-branch of the nu3 band and present a purely experimental technique that discriminates between (16)O(16)O(17)O and (16)O(17)O(16)O. Around 1040 cm(-1), differences in line positions of (16)O(17)O(16)O upto 4 x 10(-3) cm(-1) between our measurements and present spectroscopic database records (HITRAN 2004) are found.
A lightweight instrument has been developed to measure water vapor up to the lower stratosphere a... more A lightweight instrument has been developed to measure water vapor up to the lower stratosphere aboard meteorological balloons. The sensor relies on a segmented circular multipass cell which is especially suited for mobile field applications.
For small isotope effects this lead to a linear correlation: δ 17 O = n δ 18 O. 2 Actually the ma... more For small isotope effects this lead to a linear correlation: δ 17 O = n δ 18 O. 2 Actually the mass fractionation law differs for equilibrium and kinetic processes because kinetic fractionation results from motions that can often be described classically using effective masses whereas equilibrium exchange is purely a quantum phenomenon that depends on the atomic masses alone. 3 When plotted on a 3-isotope plot (δ 17 O versus δ 18 O), a line with a slope of ca. 0.52 is observed. 4 For an extensive review see and references therein.
Precision, accuracy, and temporal resolution are key to make full use of atmospheric trace gas re... more Precision, accuracy, and temporal resolution are key to make full use of atmospheric trace gas records in ice cores. These aspects will become especially crucial for ice cores that aim to extend the ice core record to the last 1.5 Myr, i.e., across the Mid Pleistocene Transition (as currently drilled within the European project Beyond EPICA -Oldest Ice Core (BE-OIC)). The ice from this period is expected to be close to bedrock and, due to glacier flow, extremely thinned with 15,000 years of climate history contained in only one meter of ice. Accordingly, for a century-scale resolution, the sample vertical extent must be reduced to a few cm containing only about 1 -2 mL air STP. We present a novel combined system for the extraction and the simultaneous measurement of CO 2 , CH 4 , and N 2 O concentrations, as well as δ 13 CO 2 , which achieves a vertical resolution of 1 -2 cm with precisions of 0.4 ppm, 3 ppb, 1 ppb and 0.04 ‰, respectively. This is accomplished by employing a directional and continuous laser induced sublimation followed by analysis of the sample gas by quantum cascade laser absorption spectroscopy (QCLAS). Besides the low sample volume requirements and the vertical resolution capabilities, the described method holds additional advantages over previous methods, including the immunity of the highly specific QCLAS analysis to drilling fluid contamination as well as the non-destructive nature of the spectroscopic gas analysis. The combined extraction and analysis system was extensively tested by sublimating gas-free ice with introduction of a standard gas to determine the accuracy and characterize potential artefacts. Moreover, Antarctic ice samples were measured to confirm the measurement performance, covering the range of variability expected in Pleistocene ice and to highlight the vertical resolution capabilities critical for its application within BE-OIC. Ice cores are unique natural archives preserving valuable information on atmospheric greenhouse gas concentrations (CO 2 , CH 4 , N 2 O) in typically centennial resolution over hundreds of thousands of years. Reconstructing paleo-atmospheric changes in these gases and their isotopic composition has provided valuable insights into their biogeochemical cycles (Blunier and 1
Mid-infrared laser spectroscopy is a proven technology for reliable and high-precision gas sensin... more Mid-infrared laser spectroscopy is a proven technology for reliable and high-precision gas sensing. With the advent of state-of-the-art laser sources, a large variety of analytical techniques has been developed, significantly extending the area of applications beyond the laboratory environment. Yet, full portability and downscaling remained a significant challenge, especially when selectivity, sensitivity and precision were to be preserved.
EGU General Assembly Conference Abstracts, Apr 1, 2018
Absorption spectroscopy is the method of choice for precise, fast, and contact free measurements ... more Absorption spectroscopy is the method of choice for precise, fast, and contact free measurements of trace gases in a large variety of research fields [e.g. 1]. Today, there is an increasing demand for com-pact and lightweight spectrometers to be deployed e.g. on board of cars, drones, or balloons. Such mobile settings enable the monitoring of trace gas concentrations at a high spatiotemporal resolution at urban, rural or industrial sites, or even in the upper atmosphere. In order to enhance precision and detection limit, absorption spectrometers make use of beam extending multipass cells (MPCs) to in-crease the interaction path length between the probe laser and the sample gas, usually to many tens of meters. Currently, these cells are the major limiting factor towards small and lightweight instruments, because the established designs are not sufficiently achieving both compactness and optical stability. Herein we present a highly promising, versatile concept for compact and well controlled beam folding. Based on the idea of toroidal circular multipass cells as proposed by Tuzson et al. [2], we reconsidered the shaping of the reflective inner surface structure to realize an optically stable beam confinement. By doing so, we combine the constructional advantages of the toroidal cell, i.e. compactness, rigidity and low weight, with optimal optical properties. In contrast to the previous solution [3], optical noise from interference fringes is inherently minimized by the optically stable cavity design. Furthermore, the present concept accepts a wide range of input beam-shapes such that the required optics for beam pre-shaping can drastically be reduced. This implies further miniaturization of any system incorporating this cell. As a proof of concept, we report sub-ppb precision (at 1 Hz) of atmospheric methane measurement in a compact setup containing our novel cell prototype. The cell of 75 mm radius and a mass of less than 200 g extends the laser beam to 10 m within an effective sampling volume of only 140 ml. The results demonstrate the potential of this concept as a versatile solution for many future size-and mass-critical spectroscopic applications.
We report on the design and performance of dual-wavelength distributed-feedback quantum cascade l... more We report on the design and performance of dual-wavelength distributed-feedback quantum cascade lasers emitting at several wavelengths in the mid-infrared spectrum, based on (i) neighbour QCLs or (ii) Vernier effect combined with digitalized gratings.
ABSTRACT Leak detection of aerosol can propellants by means of optical spectroscopy allows for fa... more ABSTRACT Leak detection of aerosol can propellants by means of optical spectroscopy allows for faster and safer operation, at much lower energy consumption than standard technologies. In this paper, a Mid-infrared (IR) optical analyzer that has been developed for ultra-fast leak detection of most common aerosol propellants such as propane and butane is presented. The performance of the instrument for application in leak detection industry was evaluated by combining the instrument with an industrial demonstrator to detect leaks of hydrocarbon gases of 0.12 ml/min, corresponding to the largest acceptable leak according to UN ADR 2007 directives. The measurements proved that the instrument can detect such leaks with a signal-to-noise ratio (SNR) better than 18 at testing speed of 500 cans/min. The overall energy consumption of the demonstrator is about 50 times lower compared to current detection systems at normal operation.
Single-piece cylindrical multipass cells effectively fold a long optical path in a small detectio... more Single-piece cylindrical multipass cells effectively fold a long optical path in a small detection volume. We present a systematic survey of various cell configurations and the respective mirror shapes for enhanced path-to-volume ratios.
We report on the development and validation of a compact laser instrument using mid-IR direct abs... more We report on the development and validation of a compact laser instrument using mid-IR direct absorption spectroscopy (DAS) for high-precision measurements of ethanol in breath-like air mixtures. Leveraging the intermittent continuous wave (iCW) driving for conventional narrow-band distributed feedback (DFB) quantum cascade laser (QCL) emitting around 9.3 µm and using a 25 m path length multiple-pass absorption cell at reduced pressure, a precision of 9 ppb (amount fraction, nmol mol -1 ) at 60 s integration time is achieved even in the presence of 5% of H 2 O and CO 2 . Thus, the instrument is well suitable for metrological studies to investigate observed, but yet unquantified, discrepancies between different breath alcohol reference-generation methods. The approach can be generalized and applied for other organic molecules in a wide range of applications.
broadly tunable mid-infrared verticalexternal-cavity surface emitting laser (VEC-SEL) is employed... more broadly tunable mid-infrared verticalexternal-cavity surface emitting laser (VEC-SEL) is employed in a direct absorption laser spectroscopic setup to measure breath acetone. The large wavelength coverage of more than 30 cm -1 at 3.38 µm allows, in addition to acetone, the simultaneous measurement of isoprene, ethanol, methanol, methane, and water. Despite the severe spectral interferences from water and alcohols, an unambiguous determination of acetone is demonstrated with a precision of 13 ppbv that is achieved after 5 min averaging at typical breath mean acetone levels in synthetic gas samples mimicking human breath.
A compact and lightweight mid-infrared laser absorption spectrometer has been developed as a mobi... more A compact and lightweight mid-infrared laser absorption spectrometer has been developed as a mobile sensing platform for high-precision atmospheric methane measurements aboard small unmanned aerial vehicles (UAVs). The instrument leverages two recent innovations: a novel segmented circular multipass cell (SC-MPC) design and a power-efficient, low-noise, intermittent continuous-wave (icw) laser driving approach. A system-on-chip hardware control and data acquisition system enables energy-efficient and fully autonomous operation. The integrated spectrometer weighs 2.1 kg (including battery) and consumes 18 W of electrical power, making it ideally suited for airborne monitoring applications. Under stable laboratory conditions, the device achieves a precision (1σ ) of 1.1 ppb within 1 s and 0.1 ppb CH 4 at 100 s averaging time. Detailed investigations were performed to identify and quantify the effects of various environmental factors, such as sudden changes in pressure, temperature, and mechanical vibrations, which commonly influence UAV-mounted sensors. The instrument was also deployed in two feasibility field studies: an artificial methane release experiment and a study on vertical profiles in the planetary boundary layer. In both cases, the spectrometer demonstrated its airborne capability of capturing subtle and/or sudden changes in atmospheric CH 4 mole fractions and providing real-time data at 1 s time resolution.
We present the continuous data record of atmospheric CO 2 isotopes measured by laser absorption s... more We present the continuous data record of atmospheric CO 2 isotopes measured by laser absorption spectroscopy for an almost four year period at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.), Switzerland. The mean annual cycles derived from data of December 2008 to September 2012 exhibit peak-to-peak amplitudes of 11.0 µmol mol -1 for CO 2 , 0.60 ‰ for δ 13 C and 0.81 ‰ for δ 18 O. The high temporal resolution of the measurements also allow us to capture variations on hourly and diurnal timescales. For CO 2 the mean diurnal peak-to-peak amplitude is about 1 µmol mol -1 in spring, autumn and winter and about 2 µmol mol -1 in summer. The mean diurnal variability in the isotope ratios is largest during the summer months too, with an amplitude of about 0.1 ‰ both in the δ 13 C and δ 18 O, and a smaller or no discernible diurnal cycle during the other seasons. The day-to-day variability, however, is much larger and depends on the origin of the air masses arriving at Jungfraujoch. Backward Lagrangian particle dispersion model simulations revealed a close link between air composition and prevailing transport regimes and could be used to explain part of the observed variability in terms of transport history and influence region. A footprint clustering showed significantly different wintertime CO 2 , δ 13 C and δ 18 O values depending on the origin and surface residence times of the air masses. Several major updates on the instrument and the calibration procedures were performed in order to further improve the data quality. We describe the new measurement and calibration setup in detail and demonstrate the enhanced performance of the analyzer. A measurement preci-sion of about 0.02 ‰ for both isotope ratios has been obtained for an averaging time of 10 min, while the accuracy was estimated to be 0.1 ‰, including the uncertainty of the calibration gases.
Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of... more Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of great scientific and commercial importance. In these instruments, the multipass cell (MPC) represents a critical element in terms of achievable size and sensitivity. Herein, we introduce a versatile MPC-concept that unifies compactness, mechanical rigidity, and optical stability. Relying on fundamental cavity design principles and modern diamond turning techniques, we have developed a segmented circular MPC that allows efficient and interference-free beam folding. A prototype cell is presented featuring up to 10 m optical path length at a total mass of less than 200 g. Incorporated in a highly compact setup without additional beam pre-shaping optics, we demonstrate a normalized noise level of low 10 -4 (2σ) at 1 Hz.
<p>Methane from facility-scale sources (e.g. landfills and oil and gas production f... more <p>Methane from facility-scale sources (e.g. landfills and oil and gas production facilities) are prone to leakage giving rise to highly uncertain emission flux estimates. To assess the overall impact of these sources, quantification from a representative set of individual sources – from which bottom-up inventories are generated - is necessary. An attractive approach to quantify emissions from diffusive and leaky sources involves deploying an unmanned aerial vehicle (UAV) equipped with a methane sensor which allows complete mapping of the spatial and temporal variability of emission plumes within a short period of time.</p><p>Atmospheric methane concentrations were measured using a Quantum Cascade Laser Absorption Spectrometer (QCLAS) developed in-house. The spectrometer reaches in-flight precision of a few ppb at 1s time resolution, and its lightweight and compact footprint (~ 2.0 kg, ~ 15.0 x 45.0 x 25.0 cm) allows it to be mounted and flown on a commercial drone.</p><p>We quantify methane emission fluxes from local sources by applying the mass balance method using the drone-based QCLAS system. The drone was flown downwind of a given source perpendicular to the main wind direction at different altitudes above ground, while geostatistical interpolation (Kriging) of the measured methane molar fractions was performed to spatially fill the gaps. The interpolated concentrations were multiplied by the cross-sectional area and the mean stream-wise wind profile obtained from a 3D sonic anemometer to get an emission flux.</p><p>We report on the analysis of how well known emissions can be reproduced using this quantification setup based on controlled release experiments. Furthermore, we discuss the sensitivity of different measurement configurations, and provide recommendations for an optimal sampling and quantification strategy. We demonstrate the suitability and flexibility of the quantification method in investigating a wide range of facility-scale sources, which are not attainable with measurements from conventional ground-based sensors.</p>
Ozone formation in the gas phase is associated with a large and unusual isotope effect of widespr... more Ozone formation in the gas phase is associated with a large and unusual isotope effect of widespread use in geochemistry and climate research. Little is known whether similar nonstandard mass dependent fractionations also occur in other recombination reactions. Here we report on the pressure and temperature dependence of the isotopic composition of ozone formed by electric discharge in molecular oxygen. Isotope signatures at low pressures show a standard mass dependent depletion, their magnitudes strongly depending on temperature. Our analysis confirms the formation of ozone at Pyrex reactor walls with an atom recombination coefficient gamma = (0.4 ± 0.1)% at room temperature and slightly higher values at lower temperatures. Thus, although neglected so far, wall assisted ozone formation is an essential part of oxygen plasma chemistry and it could also provide a mechanism explaining the presence of ozone on icy satellites. Recombination reactions on the surface are not likely to show the isotope anomalies associated with ozone formation in the gas phase.
Isotopes in Environmental and Health Studies, Mar 1, 2006
Symmetry selective detection of the (17)O containing ozone isotopomers (16)O(16)O(17)O and (16)O(... more Symmetry selective detection of the (17)O containing ozone isotopomers (16)O(16)O(17)O and (16)O(17)O(16)O requires the unambiguous identification of absorption lines. We report high resolution tuneable diode laser spectrometer measurements of (17)O containing ozone isotopomers in the R-branch of the nu3 band and present a purely experimental technique that discriminates between (16)O(16)O(17)O and (16)O(17)O(16)O. Around 1040 cm(-1), differences in line positions of (16)O(17)O(16)O upto 4 x 10(-3) cm(-1) between our measurements and present spectroscopic database records (HITRAN 2004) are found.
A lightweight instrument has been developed to measure water vapor up to the lower stratosphere a... more A lightweight instrument has been developed to measure water vapor up to the lower stratosphere aboard meteorological balloons. The sensor relies on a segmented circular multipass cell which is especially suited for mobile field applications.
For small isotope effects this lead to a linear correlation: δ 17 O = n δ 18 O. 2 Actually the ma... more For small isotope effects this lead to a linear correlation: δ 17 O = n δ 18 O. 2 Actually the mass fractionation law differs for equilibrium and kinetic processes because kinetic fractionation results from motions that can often be described classically using effective masses whereas equilibrium exchange is purely a quantum phenomenon that depends on the atomic masses alone. 3 When plotted on a 3-isotope plot (δ 17 O versus δ 18 O), a line with a slope of ca. 0.52 is observed. 4 For an extensive review see and references therein.
Precision, accuracy, and temporal resolution are key to make full use of atmospheric trace gas re... more Precision, accuracy, and temporal resolution are key to make full use of atmospheric trace gas records in ice cores. These aspects will become especially crucial for ice cores that aim to extend the ice core record to the last 1.5 Myr, i.e., across the Mid Pleistocene Transition (as currently drilled within the European project Beyond EPICA -Oldest Ice Core (BE-OIC)). The ice from this period is expected to be close to bedrock and, due to glacier flow, extremely thinned with 15,000 years of climate history contained in only one meter of ice. Accordingly, for a century-scale resolution, the sample vertical extent must be reduced to a few cm containing only about 1 -2 mL air STP. We present a novel combined system for the extraction and the simultaneous measurement of CO 2 , CH 4 , and N 2 O concentrations, as well as δ 13 CO 2 , which achieves a vertical resolution of 1 -2 cm with precisions of 0.4 ppm, 3 ppb, 1 ppb and 0.04 ‰, respectively. This is accomplished by employing a directional and continuous laser induced sublimation followed by analysis of the sample gas by quantum cascade laser absorption spectroscopy (QCLAS). Besides the low sample volume requirements and the vertical resolution capabilities, the described method holds additional advantages over previous methods, including the immunity of the highly specific QCLAS analysis to drilling fluid contamination as well as the non-destructive nature of the spectroscopic gas analysis. The combined extraction and analysis system was extensively tested by sublimating gas-free ice with introduction of a standard gas to determine the accuracy and characterize potential artefacts. Moreover, Antarctic ice samples were measured to confirm the measurement performance, covering the range of variability expected in Pleistocene ice and to highlight the vertical resolution capabilities critical for its application within BE-OIC. Ice cores are unique natural archives preserving valuable information on atmospheric greenhouse gas concentrations (CO 2 , CH 4 , N 2 O) in typically centennial resolution over hundreds of thousands of years. Reconstructing paleo-atmospheric changes in these gases and their isotopic composition has provided valuable insights into their biogeochemical cycles (Blunier and 1
Mid-infrared laser spectroscopy is a proven technology for reliable and high-precision gas sensin... more Mid-infrared laser spectroscopy is a proven technology for reliable and high-precision gas sensing. With the advent of state-of-the-art laser sources, a large variety of analytical techniques has been developed, significantly extending the area of applications beyond the laboratory environment. Yet, full portability and downscaling remained a significant challenge, especially when selectivity, sensitivity and precision were to be preserved.
EGU General Assembly Conference Abstracts, Apr 1, 2018
Absorption spectroscopy is the method of choice for precise, fast, and contact free measurements ... more Absorption spectroscopy is the method of choice for precise, fast, and contact free measurements of trace gases in a large variety of research fields [e.g. 1]. Today, there is an increasing demand for com-pact and lightweight spectrometers to be deployed e.g. on board of cars, drones, or balloons. Such mobile settings enable the monitoring of trace gas concentrations at a high spatiotemporal resolution at urban, rural or industrial sites, or even in the upper atmosphere. In order to enhance precision and detection limit, absorption spectrometers make use of beam extending multipass cells (MPCs) to in-crease the interaction path length between the probe laser and the sample gas, usually to many tens of meters. Currently, these cells are the major limiting factor towards small and lightweight instruments, because the established designs are not sufficiently achieving both compactness and optical stability. Herein we present a highly promising, versatile concept for compact and well controlled beam folding. Based on the idea of toroidal circular multipass cells as proposed by Tuzson et al. [2], we reconsidered the shaping of the reflective inner surface structure to realize an optically stable beam confinement. By doing so, we combine the constructional advantages of the toroidal cell, i.e. compactness, rigidity and low weight, with optimal optical properties. In contrast to the previous solution [3], optical noise from interference fringes is inherently minimized by the optically stable cavity design. Furthermore, the present concept accepts a wide range of input beam-shapes such that the required optics for beam pre-shaping can drastically be reduced. This implies further miniaturization of any system incorporating this cell. As a proof of concept, we report sub-ppb precision (at 1 Hz) of atmospheric methane measurement in a compact setup containing our novel cell prototype. The cell of 75 mm radius and a mass of less than 200 g extends the laser beam to 10 m within an effective sampling volume of only 140 ml. The results demonstrate the potential of this concept as a versatile solution for many future size-and mass-critical spectroscopic applications.
We report on the design and performance of dual-wavelength distributed-feedback quantum cascade l... more We report on the design and performance of dual-wavelength distributed-feedback quantum cascade lasers emitting at several wavelengths in the mid-infrared spectrum, based on (i) neighbour QCLs or (ii) Vernier effect combined with digitalized gratings.
ABSTRACT Leak detection of aerosol can propellants by means of optical spectroscopy allows for fa... more ABSTRACT Leak detection of aerosol can propellants by means of optical spectroscopy allows for faster and safer operation, at much lower energy consumption than standard technologies. In this paper, a Mid-infrared (IR) optical analyzer that has been developed for ultra-fast leak detection of most common aerosol propellants such as propane and butane is presented. The performance of the instrument for application in leak detection industry was evaluated by combining the instrument with an industrial demonstrator to detect leaks of hydrocarbon gases of 0.12 ml/min, corresponding to the largest acceptable leak according to UN ADR 2007 directives. The measurements proved that the instrument can detect such leaks with a signal-to-noise ratio (SNR) better than 18 at testing speed of 500 cans/min. The overall energy consumption of the demonstrator is about 50 times lower compared to current detection systems at normal operation.
Single-piece cylindrical multipass cells effectively fold a long optical path in a small detectio... more Single-piece cylindrical multipass cells effectively fold a long optical path in a small detection volume. We present a systematic survey of various cell configurations and the respective mirror shapes for enhanced path-to-volume ratios.
We report on the development and validation of a compact laser instrument using mid-IR direct abs... more We report on the development and validation of a compact laser instrument using mid-IR direct absorption spectroscopy (DAS) for high-precision measurements of ethanol in breath-like air mixtures. Leveraging the intermittent continuous wave (iCW) driving for conventional narrow-band distributed feedback (DFB) quantum cascade laser (QCL) emitting around 9.3 µm and using a 25 m path length multiple-pass absorption cell at reduced pressure, a precision of 9 ppb (amount fraction, nmol mol -1 ) at 60 s integration time is achieved even in the presence of 5% of H 2 O and CO 2 . Thus, the instrument is well suitable for metrological studies to investigate observed, but yet unquantified, discrepancies between different breath alcohol reference-generation methods. The approach can be generalized and applied for other organic molecules in a wide range of applications.
broadly tunable mid-infrared verticalexternal-cavity surface emitting laser (VEC-SEL) is employed... more broadly tunable mid-infrared verticalexternal-cavity surface emitting laser (VEC-SEL) is employed in a direct absorption laser spectroscopic setup to measure breath acetone. The large wavelength coverage of more than 30 cm -1 at 3.38 µm allows, in addition to acetone, the simultaneous measurement of isoprene, ethanol, methanol, methane, and water. Despite the severe spectral interferences from water and alcohols, an unambiguous determination of acetone is demonstrated with a precision of 13 ppbv that is achieved after 5 min averaging at typical breath mean acetone levels in synthetic gas samples mimicking human breath.
A compact and lightweight mid-infrared laser absorption spectrometer has been developed as a mobi... more A compact and lightweight mid-infrared laser absorption spectrometer has been developed as a mobile sensing platform for high-precision atmospheric methane measurements aboard small unmanned aerial vehicles (UAVs). The instrument leverages two recent innovations: a novel segmented circular multipass cell (SC-MPC) design and a power-efficient, low-noise, intermittent continuous-wave (icw) laser driving approach. A system-on-chip hardware control and data acquisition system enables energy-efficient and fully autonomous operation. The integrated spectrometer weighs 2.1 kg (including battery) and consumes 18 W of electrical power, making it ideally suited for airborne monitoring applications. Under stable laboratory conditions, the device achieves a precision (1σ ) of 1.1 ppb within 1 s and 0.1 ppb CH 4 at 100 s averaging time. Detailed investigations were performed to identify and quantify the effects of various environmental factors, such as sudden changes in pressure, temperature, and mechanical vibrations, which commonly influence UAV-mounted sensors. The instrument was also deployed in two feasibility field studies: an artificial methane release experiment and a study on vertical profiles in the planetary boundary layer. In both cases, the spectrometer demonstrated its airborne capability of capturing subtle and/or sudden changes in atmospheric CH 4 mole fractions and providing real-time data at 1 s time resolution.
We present the continuous data record of atmospheric CO 2 isotopes measured by laser absorption s... more We present the continuous data record of atmospheric CO 2 isotopes measured by laser absorption spectroscopy for an almost four year period at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.), Switzerland. The mean annual cycles derived from data of December 2008 to September 2012 exhibit peak-to-peak amplitudes of 11.0 µmol mol -1 for CO 2 , 0.60 ‰ for δ 13 C and 0.81 ‰ for δ 18 O. The high temporal resolution of the measurements also allow us to capture variations on hourly and diurnal timescales. For CO 2 the mean diurnal peak-to-peak amplitude is about 1 µmol mol -1 in spring, autumn and winter and about 2 µmol mol -1 in summer. The mean diurnal variability in the isotope ratios is largest during the summer months too, with an amplitude of about 0.1 ‰ both in the δ 13 C and δ 18 O, and a smaller or no discernible diurnal cycle during the other seasons. The day-to-day variability, however, is much larger and depends on the origin of the air masses arriving at Jungfraujoch. Backward Lagrangian particle dispersion model simulations revealed a close link between air composition and prevailing transport regimes and could be used to explain part of the observed variability in terms of transport history and influence region. A footprint clustering showed significantly different wintertime CO 2 , δ 13 C and δ 18 O values depending on the origin and surface residence times of the air masses. Several major updates on the instrument and the calibration procedures were performed in order to further improve the data quality. We describe the new measurement and calibration setup in detail and demonstrate the enhanced performance of the analyzer. A measurement preci-sion of about 0.02 ‰ for both isotope ratios has been obtained for an averaging time of 10 min, while the accuracy was estimated to be 0.1 ‰, including the uncertainty of the calibration gases.
Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of... more Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of great scientific and commercial importance. In these instruments, the multipass cell (MPC) represents a critical element in terms of achievable size and sensitivity. Herein, we introduce a versatile MPC-concept that unifies compactness, mechanical rigidity, and optical stability. Relying on fundamental cavity design principles and modern diamond turning techniques, we have developed a segmented circular MPC that allows efficient and interference-free beam folding. A prototype cell is presented featuring up to 10 m optical path length at a total mass of less than 200 g. Incorporated in a highly compact setup without additional beam pre-shaping optics, we demonstrate a normalized noise level of low 10 -4 (2σ) at 1 Hz.
<p>Methane from facility-scale sources (e.g. landfills and oil and gas production f... more <p>Methane from facility-scale sources (e.g. landfills and oil and gas production facilities) are prone to leakage giving rise to highly uncertain emission flux estimates. To assess the overall impact of these sources, quantification from a representative set of individual sources – from which bottom-up inventories are generated - is necessary. An attractive approach to quantify emissions from diffusive and leaky sources involves deploying an unmanned aerial vehicle (UAV) equipped with a methane sensor which allows complete mapping of the spatial and temporal variability of emission plumes within a short period of time.</p><p>Atmospheric methane concentrations were measured using a Quantum Cascade Laser Absorption Spectrometer (QCLAS) developed in-house. The spectrometer reaches in-flight precision of a few ppb at 1s time resolution, and its lightweight and compact footprint (~ 2.0 kg, ~ 15.0 x 45.0 x 25.0 cm) allows it to be mounted and flown on a commercial drone.</p><p>We quantify methane emission fluxes from local sources by applying the mass balance method using the drone-based QCLAS system. The drone was flown downwind of a given source perpendicular to the main wind direction at different altitudes above ground, while geostatistical interpolation (Kriging) of the measured methane molar fractions was performed to spatially fill the gaps. The interpolated concentrations were multiplied by the cross-sectional area and the mean stream-wise wind profile obtained from a 3D sonic anemometer to get an emission flux.</p><p>We report on the analysis of how well known emissions can be reproduced using this quantification setup based on controlled release experiments. Furthermore, we discuss the sensitivity of different measurement configurations, and provide recommendations for an optimal sampling and quantification strategy. We demonstrate the suitability and flexibility of the quantification method in investigating a wide range of facility-scale sources, which are not attainable with measurements from conventional ground-based sensors.</p>
Ozone formation in the gas phase is associated with a large and unusual isotope effect of widespr... more Ozone formation in the gas phase is associated with a large and unusual isotope effect of widespread use in geochemistry and climate research. Little is known whether similar nonstandard mass dependent fractionations also occur in other recombination reactions. Here we report on the pressure and temperature dependence of the isotopic composition of ozone formed by electric discharge in molecular oxygen. Isotope signatures at low pressures show a standard mass dependent depletion, their magnitudes strongly depending on temperature. Our analysis confirms the formation of ozone at Pyrex reactor walls with an atom recombination coefficient gamma = (0.4 ± 0.1)% at room temperature and slightly higher values at lower temperatures. Thus, although neglected so far, wall assisted ozone formation is an essential part of oxygen plasma chemistry and it could also provide a mechanism explaining the presence of ozone on icy satellites. Recombination reactions on the surface are not likely to show the isotope anomalies associated with ozone formation in the gas phase.
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Papers by Béla Tuzson