Eddy-covariance CO2 flux measurements using open- and closed-path CO2 analysers: Corrections for analyser water vapour sensitivity and damping of fluctuations in air sampling tubes

1990 ◽  
Vol 53 (1-2) ◽  
pp. 63-76 ◽  
Author(s):  
R. Leuning ◽  
J. Moncrieff
Keyword(s):  
Water Vapour ◽  
Eddy Covariance ◽  
Air Sampling ◽  
Co2 Flux ◽  
Closed Path ◽  
Flux Measurements

scholarly journals Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

2018 ◽  
Vol 11 (11) ◽  
pp. 6075-6090 ◽  
Author(s):  
Brian J. Butterworth ◽  
Brent G. T. Else
Keyword(s):  
Carbon Dioxide ◽  
Sea Ice ◽  
Eddy Covariance ◽  
Co2 Flux ◽  
Carbon Dioxide Flux ◽  
The Arctic ◽  
Closed Path ◽  
Eddy Covariance Method ◽  
Open Path ◽  
Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

scholarly journals Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

2018 ◽  
Author(s):  
Brian J. Butterworth ◽  
Brent G. T. Else
Keyword(s):  
Carbon Dioxide ◽  
Sea Ice ◽  
Eddy Covariance ◽  
Co2 Flux ◽  
Carbon Dioxide Flux ◽  
The Arctic ◽  
Closed Path ◽  
Eddy Covariance Method ◽  
Open Path ◽  
Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10-m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from four months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar/wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

scholarly journals Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system

2015 ◽  
Vol 8 (10) ◽  
pp. 4123-4131 ◽  
Author(s):  
J. B. Wu ◽  
X. Y. Zhou ◽  
A. Z. Wang ◽  
F. H. Yuan
Keyword(s):  
Water Vapor ◽  
Eddy Covariance ◽  
Time Lag ◽  
Sonic Anemometer ◽  
Co2 Flux ◽  
Surface Energy Budget ◽  
Closed Path ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements

Abstract. Eddy covariance using infrared gas analyzes has been a useful tool for gas exchange measurements between soil, vegetation and the atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO2 flux estimations, while lacking in the comparison of water vapor flux estimations. In this study, the specific performance of water vapor flux measurements of an open-path eddy covariance (OP) system was compared against a CP system over a tall temperate forest in northeastern China. The results show that the fluxes from the OP system (LEop) were generally greater than the LEcp though the two systems shared one sonic anemometer. The tube delay of closed-path analyzer depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of LEcp between the forest and atmosphere, while slight systematic overestimation was also found for covariance maximization method with single broad time lag search window. After the optimized time lag compensation was made, the average difference between the 30 min LEop and LEcp was generally within 6.0 %. Integrated over the annual cycle, the CP system yielded a 5.1 % underestimation of forest evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr−1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analyzers, and it also suggests that some of the imbalance of the surface energy budget in flux sites is possibly caused by the systematic underestimation of water vapor fluxes measured with closed-path eddy covariance systems.

scholarly journals Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system

2015 ◽  
Vol 8 (5) ◽  
pp. 4711-4736
Author(s):  
J. B. Wu ◽  
X. Y. Zhou ◽  
A. Z. Wang ◽  
F. H. Yuan
Keyword(s):  
Water Vapor ◽  
Eddy Covariance ◽  
Time Lag ◽  
Sonic Anemometer ◽  
Co2 Flux ◽  
Closed Path ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements ◽  
Eddy Covariance System

Abstract. Eddy covariance using infrared gas analyses has been a useful tool for gas exchange measurements between soil, vegetation and atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO2 flux estimations, while lacking in the comparison of water vapor flux estimations. In this study, the specific performance of water vapor flux measurements of an open-path eddy covariance (OP) system was compared against a CP system over a tall temperate forest in Northeast China. The results show that the fluxes from the OP system (LEop) were generally greater than the (LEcp though the two systems shared one sonic anemometer. The tube delay of closed-path analyser depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of (LEcp between the forest and atmosphere, while slight systematic overestimation was also found for covariance maximization method with single broad time lag search window. After the optimized time lag compensation was made, the average difference between the 30 min (LEop and (LEcp was generally within 6%. Integrated over the annual cycle, the CP system yielded a 5.1% underestimation of forest evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr−1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analysers, and it also suggests that when discuss the energy balance closure problem in flux sites with closed-path eddy covariance systems, it has to be aware that some of the imbalance is possibly caused by the systematic underestimation of water vapor fluxes.

scholarly journals Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance

2016 ◽  
Vol 9 (11) ◽  
pp. 5509-5522 ◽  
Author(s):  
Mingxi Yang ◽  
John Prytherch ◽  
Elena Kozlova ◽  
Margaret J. Yelland ◽  
Deepulal Parenkat Mony ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Detection Limits ◽  
Co2 Flux ◽  
Closed Path ◽  
Mixing Ratios ◽  
Dry Mixing ◽  
Flux Measurements ◽  
The Mean ◽  
Set Up ◽  
Carbon Dioxide Co2

Abstract. In recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO2), methane (CH4), and water vapour (H2O) have become available. Here we compare the performance of two leading models – the Picarro G2311-f and the Los Gatos Research (LGR) Fast Greenhouse Gas Analyzer (FGGA) at a coastal site. Both instruments can compute dry mixing ratios of CO2 and CH4 based on concurrently measured H2O, temperature, and pressure. Additionally, we used a high throughput Nafion dryer to physically remove H2O from the Picarro airstream. Observed air–sea CO2 and CH4 fluxes from these two analysers, averaging about 12 and 0.12 mmol m−2 day−1 respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO2 and CH4 fluxes downstream of a long inlet, the numerical H2O corrections appear to be reasonably effective and lead to results that are comparable to physical removal of H2O with a Nafion dryer in the mean. We estimate the high-frequency attenuation of fluxes in our closed-path set-up, which was relatively small ( ≤  10 %) for CO2 and CH4 but very large for the more polar H2O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m−2 day−1 for CO2 and 0.02 mmol m−2 day−1 for CH4. For the LGR these detection limits were about 8 and 0.05 mmol m−2 day−1. Using global maps of monthly mean air–sea CO2 flux as reference, we estimate that the Picarro and LGR can resolve hourly CO2 fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH4 from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may improve closer to the coast.

scholarly journals Comparison of two closed-path cavity based spectrometers for measuring air-water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance

2016 ◽  
Author(s):  
Mingxi Yang ◽  
John Prytherch ◽  
Elena Kozlova ◽  
Margaret J. Yelland ◽  
Deepulal Parenkat Mony ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Detection Limits ◽  
Co2 Flux ◽  
Closed Path ◽  
Mixing Ratios ◽  
Air Stream ◽  
Dry Mixing ◽  
Flux Measurements ◽  
Carbon Dioxide Co2 ◽  
Lower Noise

Abstract. In recent years several commercialized closed-path cavity based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO2), methane (CH4), and water vapor (H2O) have become available. Here we compare the performance of two state-of-the-art models – the Picarro G2311-f and the Los Gatos Research (LGR) FGGA at a coastal site. Both instruments can compute dry mixing ratios of CO2 and CH4 based on the concurrently measured H2O. Additionally, we used a high throughput Nafion dryer to physically remove H2O from the Picarro air stream. Observed air-sea CO2 and CH4 fluxes from these two analyzers, averaging about 12 mmol m−2 d−1 and 0.12 mmol m−2 d−1 respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO2 and CH4 fluxes, the numerical H2O corrections appear to be effective and lead to results that are comparable to physical removal of H2O with a Nafion dryer. We estimate the high frequency attenuation of fluxes in our closed-path setup, which was relatively small (≤ 10 %) for CO2 and CH4 but very large for the much stickier H2O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m−2 d−1 for CO2 and 0.02 mmol m−2 d−1 for CH4. For the LGR these detection limits were about 8 mmol m−2 d−1 and 0.05 mmol m−2 d−1. Using global maps of monthly-mean air-sea CO2 flux as reference, we estimate that the Picarro and LGR can resolve hourly CO2 fluxes from roughly 40 % and 4 % of the world’s oceans, respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH4 from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may improve closer to the coast.

scholarly journals Eddy covariance methane measurements at a Ponderosa pine plantation in California

2009 ◽  
Vol 9 (21) ◽  
pp. 8365-8375 ◽  
Author(s):  
C. J. P. P. Smeets ◽  
R. Holzinger ◽  
I. Vigano ◽  
A. H. Goldstein ◽  
T. Röckmann
Keyword(s):  
Eddy Covariance ◽  
Ponderosa Pine ◽  
Power Spectra ◽  
Methane Flux ◽  
Forest Site ◽  
Phase Lag ◽  
Closed Path ◽  
Pine Plantation ◽  
Model Calculations ◽  
Flux Measurements

Abstract. Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC) technique instead. The EC technique is advantageous because it allows continuous flux measurements integrating over a larger and more representative area including the complete ecosystem, and allows fluxes to be observed as environmental conditions change naturally without disturbance. We deployed the closed-path Fast Methane analyzer (FMA) from Los Gatos Research Ltd and demonstrate its performance for EC measurements at a Ponderosa pine plantation at the Blodgett Forest site in central California. The fluctuations of the CH4 concentration measured at 10 Hz appear to be small and their standard deviation is comparable to the magnitude of the signal noise (±5 ppbv). Consequently, the power spectra typically have a white noise signature at the high frequency end (a slope of +1). Nevertheless, in the frequency range important for turbulent exchange, the cospectra of CH4 compare very well with all other scalar cospectra confirming the quality of the FMA measurements are good for the EC technique. We furthermore evaluate the complications of combined open and closed-path measurements when applying the Webb-Pearman-Leuning (WPL) corrections (Webb et al., 1980) and the consequences of a phase lag between the water vapor and methane signal inside the closed path system. The results of diurnal variations of CH4 concentrations and fluxes are summarized and compared to the monthly results of process-based model calculations.

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