scholarly journals An open path, fast response infrared absorption gas analyzer for H2O and CO2

1992 ◽  
Vol 59 (3) ◽  
pp. 243-256 ◽  
Author(s):  
David L. Auble ◽  
Tilden P. Meyers
Keyword(s):  
Infrared Absorption ◽  
Fast Response ◽  
Gas Analyzer ◽  
Open Path

Temperature Induced Spectroscopic Line-broadening Effects in Open-path Eddy Covariance CO2 Flux

2020 ◽  
Author(s):  
Ivan Bogoev ◽  
David Holl
Keyword(s):  
Eddy Covariance ◽  
Air Temperature ◽  
Broad Band ◽  
Fast Response ◽  
Optical Path ◽  
Pass Band ◽  
Line Broadening ◽  
Gas Analyzer ◽  
Gas Density ◽  
Open Path

<p>Open-path eddy covariance systems, based on broad-band non-dispersive infrared (NDIR) gas analyzers, are widely used for CO<sub>2</sub> and H<sub>2</sub>O flux measurements in remote locations around the world, because of their low power consumption, fast response and reliable operation. Nevertheless, agreement between open- and closed-path CO<sub>2 </sub>fluxes has limited inter-site comparability, especially in cold or non-growing seasons and low-flux environments, where physiologically unreasonable CO<sub>2</sub> uptake is often observed by the open-path systems. A possible explanation is sensor-surface heating from internal-electronics power dissipation and solar radiation, which causes unaccounted gas density changes in the optical path. Fast-response thermometers, co-located with the gas analyzer, have been used to correct these effects. However, the fragility of the thermometers has prevented the wide adoption of this approach.</p><p>A challenge for the open-path sensor design is that in-situ air temperature affects not only the gas density but also the broadened half-width and intensity of the spectral absorption lines. We hypothesize that fast air temperature fluctuations in the optical path of the gas analyzer can change the amount of absorbed light and cause errors in the CO<sub>2</sub> concentration measurement. Because of the natural covariance of sensible and CO<sub>2</sub> fluxes, such errors are well correlated with the vertical wind and can potentially propagate into flux calculations.</p><p>We used spectral-line parameters, obtained from the high-resolution transmission molecular spectroscopic database (HITRAN), to evaluate the temperature effects on the integrated absorption spectra of CO<sub>2</sub>-air-mixtures across the 4.2 to 4.3 μm infrared active region utilized by NDIR analyzers.  Results show that air temperature strongly influences absorption, and if not properly corrected, potentially introduces biases in the CO<sub>2</sub> concentration measurements.  Strong lines exhibit Doppler broadening, where the line peak and width decline with increasing temperatures, causing underestimation of CO<sub>2</sub> concentration. Weak lines exhibit the opposite behavior. Based on our simulations, optimizing the optical filter pass-band can balance these opposing effects and greatly reduce the temperature dependence. In practice, manufacturing tolerances, shifts in the center wavelength, and the temperature sensitivity of the optical filters prevent complete elimination of the temperature-line broadening. A 13 nanometer shift in the filter pass band can introduce a 0.008 mmol m<sup>-3</sup> K<sup>-1</sup> underestimation in the CO<sub>2</sub> concentration, which is a 0.67 μmol m<sup>-2</sup> s<sup>-1</sup> systematic error in CO<sub>2</sub> flux per 100 watts of sensible heat flux.</p>

scholarly journals Precise multispecies agricultural gas flux determined using broadband open-path dual-comb spectroscopy

2021 ◽  
Vol 7 (14) ◽  
pp. eabe9765
Author(s):  
Daniel I. Herman ◽  
Chinthaka Weerasekara ◽  
Lindsay C. Hutcherson ◽  
Fabrizio R. Giorgetta ◽  
Kevin C. Cossel ◽  
...  
Keyword(s):  
Ecological Monitoring ◽  
Trace Gas ◽  
Gas Analyzer ◽  
Gas Flux ◽  
Time Resolved ◽  
Trace Gas Emissions ◽  
Open Path ◽  
Statistical Precision ◽  
Methane Fluxes ◽  
Flux Quantification

Advances in spectroscopy have the potential to improve our understanding of agricultural processes and associated trace gas emissions. We implement field-deployed, open-path dual-comb spectroscopy (DCS) for precise multispecies emissions estimation from livestock. With broad atmospheric dual-comb spectra, we interrogate upwind and downwind paths from pens containing approximately 300 head of cattle, providing time-resolved concentration enhancements and fluxes of CH4, NH3, CO2, and H2O. The methane fluxes determined from DCS data and fluxes obtained with a colocated closed-path cavity ring-down spectroscopy gas analyzer agree to within 6%. The NH3 concentration retrievals have sensitivity of 10 parts per billion and yield corresponding NH3 fluxes with a statistical precision of 8% and low systematic uncertainty. Open-path DCS offers accurate multispecies agricultural gas flux quantification without external calibration and is easily extended to larger agricultural systems where point-sampling-based approaches are insufficient, presenting opportunities for field-scale biogeochemical studies and ecological monitoring.

scholarly journals Compact Open-Path Sensor for Fast Measurements of CO2 and H2O using Scanned-Wavelength Modulation Spectroscopy with 1f-Phase Method

Sensors ◽  
2020 ◽  
Vol 20 (7) ◽  
pp. 1910
Author(s):  
Xiang Li ◽  
Feng Yuan ◽  
Mai Hu ◽  
Bin Chen ◽  
Yabai He ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Fast Response ◽  
Wavelength Modulation Spectroscopy ◽  
Phase Method ◽  
High Temporal Resolution ◽  
Wavelength Modulation ◽  
Modulation Spectroscopy ◽  
Open Path ◽  
Averaging Time ◽  
Term Performance

We report here the development of a compact, open-path CO2 and H2O sensor based on the newly introduced scanned-wavelength modulation spectroscopy with the first harmonic phase angle (scanned-WMS-θ1f) method for high-sensitivity, high temporal resolution, ground-based measurements. The considerable advantage of the sensor, compared with existing commercial ones, lies in its fast response of 500 Hz that makes this instrument ideal for resolving details of high-frequency turbulent motion in exceptionally dynamic coastal regions. The good agreement with a commercial nondispersive infrared analyzer supports the utility and accuracy of the sensor. Allan variance analysis shows that the concentration measurement sensitivities can reach 62 ppb CO2 in 0.06 s and 0.89 ppm H2O vapor in 0.26 s averaging time. Autonomous field operation for 15-day continuous measurements of greenhouse gases (CO2/H2O) was performed on a shore-based monitoring tower in Daya Bay, demonstrating the sensor’s long-term performance. The capability for high-quality fast turbulent atmospheric gas observations allow the potential for better characterization of oceanographic processes.

scholarly journals Performance Evaluation of an Integrated Open-Path Eddy Covariance System in a Cold Desert Environment

2016 ◽  
Vol 33 (11) ◽  
pp. 2385-2399 ◽  
Author(s):  
Wei Wang ◽  
Jiaping Xu ◽  
Yunqiu Gao ◽  
Ivan Bogoev ◽  
Jian Cui ◽  
...  
Keyword(s):  
Performance Evaluation ◽  
Eddy Covariance ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Winter Season ◽  
Populus Euphratica ◽  
Tarim River ◽  
Tarim River Basin ◽  
Gas Analyzer ◽  
Open Path

AbstractPerformance evaluation of an integrated eddy covariance (EC) instrument called the IRGASON, with a separated EC for reference, was conducted in a desert riparian Populus euphratica stand in the lower Tarim River basin in northwestern China. The separated EC consisted of an open-path gas analyzer and a sonic anemometer separated by 20 cm. The IRGASON integrates an open-path gas analyzer and a sonic anemometer into the same sensing volume, thus eliminating sensor separation in comparison to the traditional open-path EC setup. Integrating the infrared gas analyzer’s sensing head into the sensing volume of the sonic anemometer had negligible effects on wind speed and friction velocity observations of the IRGASON. Physiologically unreasonable daytime CO2 uptake was observed by both systems during the cold winter season (mean air temperature of −6.7°C), when the trees were dormant without any photosynthetic activities. The mean midday CO2 flux was −1.65 and −1.61 μmol m−2 s−1 for the IRGASON and the separated EC setup, respectively. No evidence was found for sensor self-heating as the cause of the apparent uptake CO2 flux. Instead, the uptake CO2 flux appeared to be an artifact of the spectroscopic effect of the IRGASON’s gas analyzer. After adjusting for this spectroscopic effect using a relationship with the sensible heat flux, the wintertime IRGASON CO2 flux became physiologically reasonable (mean value of −0.04 μmol m−2 s−1).

scholarly journals Two instruments based on differential optical absorption spectroscopy (DOAS) to measure accurate ammonia concentrations in the atmosphere

2011 ◽  
Vol 4 (4) ◽  
pp. 5037-5078
Author(s):  
H. Volten ◽  
J. B. Bergwerff ◽  
M. Haaima ◽  
D. E. Lolkema ◽  
A. J. C. Berkhout ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Monitoring Network ◽  
Fast Response ◽  
High Accuracy ◽  
Differential Optical Absorption Spectroscopy ◽  
Optical Absorption Spectroscopy ◽  
Open Path ◽  
Set Up ◽  
Similar Accuracy

Abstract. We present two Differential Optical Absorption Spectroscopy (DOAS) instruments built at RIVM, the RIVM DOAS and the miniDOAS. Both instruments provide virtually interference free measurements of NH3 concentrations in the atmosphere, since they measure over an open path, without suffering from inlet problems or interference problems by ammonium aerosols dissociating on tubes or filters. They measure concentrations up to at least 200 μg m−3, have a fast response, low maintenance demands, and a high up-time. The RIVM DOAS has a high accuracy of typically 0.15 μg m−3 for ammonia over 5-min averages and over a total light path of 100 m. The miniDOAS has been developed for application in measurement networks such as the Dutch National Air Quality Monitoring Network (LML). Compared to the RIVM DOAS it has a similar accuracy, but is significantly reduced in size, costs, and handling complexity. The RIVM DOAS and miniDOAS results showed excellent agreement (R2 = 0.996) during a field measurement campaign in Vredepeel, the Netherlands. This measurement site is located in an agricultural area and is characterized by highly variable, but on average high ammonia concentrations in the air. The RIVM-DOAS and miniDOAS results were compared to the results of the AMOR instrument, a continuous-flow wet denuder system, which is currently used in the LML. Averaged over longer time spans of typically a day the (mini)DOAS and AMOR results agree reasonably well, although an offset of the AMOR values compared to the (mini)DOAS results exists. On short time scales the (mini)DOAS shows a faster response and does not show the memory effects due to inlet tubing and transport of absorption fluids encountered by the AMOR. Due to its high accuracy, high uptime, low maintenance and its open path, the (mini)DOAS shows a good potential for flux measurements by using two (or more) systems in a gradient set-up and applying the aerodynamic gradient technique.

Effect of open-path gas analyzer wetness on eddy covariance flux measurements: A proposed solution

2008 ◽  
Vol 148 (10) ◽  
pp. 1563-1573 ◽  
Author(s):  
Bert G. Heusinkveld ◽  
Adrie F.G. Jacobs ◽  
Albert A.M. Holtslag
Keyword(s):  
Eddy Covariance ◽  
Gas Analyzer ◽  
Open Path ◽  
Flux Measurements

scholarly journals A Fast-Response Automated Gas Equilibrator (FaRAGE) for continuous in situ measurement of CH<sub>4</sub> and CO<sub>2</sub> dissolved in water

2020 ◽  
Vol 24 (7) ◽  
pp. 3871-3880 ◽  
Author(s):  
Shangbin Xiao ◽  
Liu Liu ◽  
Wei Wang ◽  
Andreas Lorke ◽  
Jason Woodhouse ◽  
...  
Keyword(s):  
Response Time ◽  
Greenhouse Gas ◽  
Three Dimensional ◽  
Fast Response ◽  
In Situ Measurement ◽  
Inland Waters ◽  
Gas Analyzer ◽  
Potential Applications ◽  
Carbon Dioxide Co2

Abstract. Biogenic greenhouse gas emissions, e.g., of methane (CH4) and carbon dioxide (CO2) from inland waters, contribute substantially to global warming. In aquatic systems, dissolved greenhouse gases are highly heterogeneous in both space and time. To better understand the biological and physical processes that affect sources and sinks of both CH4 and CO2, their dissolved concentrations need to be measured with high spatial and temporal resolution. To achieve this goal, we developed the Fast-Response Automated Gas Equilibrator (FaRAGE) for real-time in situ measurement of dissolved CH4 and CO2 concentrations at the water surface and in the water column. FaRAGE can achieve an exceptionally short response time (t95 %=12 s when including the response time of the gas analyzer) while retaining an equilibration ratio of 62.6 % and a measurement accuracy of 0.5 % for CH4. A similar performance was observed for dissolved CO2 (t95 %=10 s, equilibration ratio 67.1 %). An equilibration ratio as high as 91.8 % can be reached at the cost of a slightly increased response time (16 s). The FaRAGE is capable of continuously measuring dissolved CO2 and CH4 concentrations in the nM-to-sub mM (10−9–10−3 mol L−1) range with a detection limit of sub-nM (10−10 mol L−1), when coupling with a cavity ring-down greenhouse gas analyzer (Picarro GasScouter). FaRAGE allows for the possibility of mapping dissolved concentration in a “quasi” three-dimensional manner in lakes and provides an inexpensive alternative to other commercial gas equilibrators. It is simple to operate and suitable for continuous monitoring with a strong tolerance for suspended particles. While the FaRAGE is developed for inland waters, it can be also applied to ocean waters by tuning the gas–water mixing ratio. The FaRAGE is easily adapted to suit other gas analyzers expanding the range of potential applications, including nitrous oxide and isotopic composition of the gases.

scholarly journals A Fast-response automated gas equilibrator (FaRAGE) for continuous in situ measurement of methane dissolved in water

2020 ◽  
Author(s):  
Shangbin Xiao ◽  
Liu Liu ◽  
Wei Wang ◽  
Andreas Lorke ◽  
Jason Woodhouse ◽  
...  
Keyword(s):  
Response Time ◽  
Three Dimensional ◽  
Fast Response ◽  
In Situ Measurement ◽  
Gas Analyzer ◽  
Biogenic Methane ◽  
Lakes And Reservoirs ◽  
Ch4 Concentration ◽  
Dissolved Ch4 Concentration

Abstract. Biogenic methane (CH4) emissions from inland waters contribute substantially to global warming. In aquatic systems, CH4 dissolved in freshwater lakes and reservoirs is highly heterogeneous both in space and time. To better understand the biological and physical processes that affect sources and sinks of CH4 in lakes and reservoirs, dissolved CH4 needs to be measured with a highest temporal resolution. To achieve this goal, we developed the Fast-Response Automated Gas Equilibrator (FaRAGE) for real-time in situ measurement of dissolved CH4 concentration at the water surface and in the water column. FaRAGE can achieve an exceptionally short response time (t95 % = 12 s when including the response time of the gas analyzer) while retaining an equilibration ratio of 63 % and a measurement accuracy of 0.5 %. An equilibration ratio as high as 91.8 % can be reached at the cost of a slightly increased response time (16 s). The FaRAGE is capable of continuously measuring dissolved CH4 concentrations in the nM-to-mM (10−9–10−3 mol L−1) range with a detection limit of sub-nM (10−10 mol L−1), when coupled with a cavity ring-down greenhouse gas analyzer (Picarro GasScouter). It enables the possibility of mapping dissolved CH4 concentration in a quasi three-dimensional manner in lakes. The FaRAGE is simple to operate, inexpensive, and suitable for continuous monitoring with a strong tolerance to suspended particles. The easy adaptability to other gas analyzers such as Ultra-portable Los Gatos and stable isotopic gas analyzer (Picarro G2132-i) also provides the potential for many further applications, e.g. measuring dissolved 13δC-CH4 and CO2.

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