scholarly journals Disjunct eddy covariance technique for trace gas flux measurements

2001 ◽  
Vol 28 (16) ◽  
pp. 3139-3142 ◽  
Author(s):  
H. J. I. Rinne ◽  
A. B. Guenther ◽  
C. Warneke ◽  
J. A. de Gouw ◽  
S. L. Luxembourg
Keyword(s):  
Eddy Covariance ◽  
Trace Gas ◽  
Gas Flux ◽  
Eddy Covariance Technique ◽  
Flux Measurements

scholarly journals True eddy accumulation trace gas flux measurements: proof-of-concept

2019 ◽  
Author(s):  
Lukas Siebicke ◽  
Anas Emad
Keyword(s):  
Water Vapor ◽  
Flow Control ◽  
Eddy Covariance ◽  
Mass Flow ◽  
Fast Response ◽  
Trace Gas ◽  
Proof Of Concept ◽  
Gas Flux ◽  
Flux Measurements ◽  
The Impact

Abstract. Micrometeorological methods to quantify fluxes of atmospheric constituents are key to understanding and managing the impact of land surface sources and sinks on air quality and atmospheric composition. Important greenhouse gases are water vapor, carbon dioxide, methane, and nitrous oxide. Further important atmospheric constituents are aerosols which impact air quality and cloud formation, and volatile organic compounds. Many atmospheric constituents therefore critically affect the health of ecosystems, and humans as well as climate. The micrometeorological eddy covariance (EC) method has evolved as the method-of-choice for CO2 and water vapor flux measurements using fast-response gas analyzers. While the EC method has also been used to measure other atmospheric constituents including methane, nitrous oxide, and ozone, the often relatively small fluxes of these constituents over ecosystems are much more challenging to measure by eddy covariance than CO2 and water vapor fluxes. For many further atmospheric constituents, eddy covariance is not an option due to the lack of sufficiently accurate and fast-response gas analyzers. Therefore, alternative flux measurement methods are required for the observation of atmospheric constituent fluxes for which no fast-response gas analyzers exist or which require more accurate measurements. True eddy accumulation (TEA) is a direct flux measurement technique capable of using slow-response gas analyzers. Unlike its more frequently used derivative, known as the relaxed eddy accumulation (REA) method, TEA does not require the use of proxies and is therefore superior to the indirect REA method. The true eddy accumulation method is by design ideally suited for measuring a wide range of trace gases and other conserved constituents transported with the air. This is because TEA obtains whole air samples and is, in combination with constituent-specific fast or slow analyzers, a universal method for conserved scalars. Despite the recognized value of the method, true eddy accumulation flux measurements remained very challenging to perform as they require fast and dynamic modulation of the air sampling mass flow rate proportional to the magnitude of the instantaneous vertical wind velocity. Appropriate techniques for dynamic mass flow control have long been unavailable, preventing the unlocking of the TEA method's potential for more than 40 years. Recently, a new dynamic and accurate mass flow controller which can resolve turbulence at a frequency of 10 Hz and higher has been developed by the author. This study presents the proof-of-concept that practical true eddy accumulation trace gas flux measurements are possible today using dynamic mass flow control, advanced real-time processing of wind measurements, and fully automatic gas handling. We describe setup and methods of the TEA and EC reference flux measurements. The experiment was conducted over grassland and comprised seven days of continuous flux measurements at 30-min flux integration intervals. The results show that fluxes obtained by TEA compared favourably to EC reference flux measurements with coefficients of determination of up to 86 % and a slope of 0.98. We present a quantitative analysis of uncertainties of the mass flow control system, the gas analyzer and gas handling system and their impact on trace gas flux uncertainty, the impact of different approaches to coordinate rotation and uncertainties of vertical wind velocity measurements. Challenges of TEA are highlighted and solutions presented. The current results are put into context of previous works. Finally, based on the current successful proof-of-concept, we suggest specific improvements towards long-term and reliable true eddy accumulation flux measurements.

scholarly journals True eddy accumulation trace gas flux measurements: proof of concept

2019 ◽  
Vol 12 (8) ◽  
pp. 4393-4420 ◽  
Author(s):  
Lukas Siebicke ◽  
Anas Emad
Keyword(s):  
Water Vapor ◽  
Flow Control ◽  
Eddy Covariance ◽  
Mass Flow ◽  
Fast Response ◽  
Trace Gas ◽  
Proof Of Concept ◽  
Gas Flux ◽  
Flux Measurements ◽  
The Impact

Abstract. Micrometeorological methods to quantify fluxes of atmospheric constituents are key to understanding and managing the impact of land surface sources and sinks on air quality and atmospheric composition. Important greenhouse gases are water vapor, carbon dioxide, methane, and nitrous oxide. Further important atmospheric constituents are aerosols, which impact air quality and cloud formation, and volatile organic compounds. Many atmospheric constituents therefore critically affect the health of ecosystems and humans, as well as climate. The micrometeorological eddy covariance (EC) method has evolved as the method of choice for CO2 and water vapor flux measurements using fast-response gas analyzers. While the EC method has also been used to measure other atmospheric constituents including methane, nitrous oxide, and ozone, the often relatively small fluxes of these constituents over ecosystems are much more challenging to measure using eddy covariance than CO2 and water vapor fluxes. For many further atmospheric constituents, eddy covariance is not an option due to the lack of sufficiently accurate and fast-response gas analyzers. Therefore, alternative flux measurement methods are required for the observation of atmospheric constituent fluxes for which no fast-response gas analyzers exist or which require more accurate measurements. True eddy accumulation (TEA) is a direct flux measurement technique capable of using slow-response gas analyzers. Unlike its more frequently used derivative, known as the relaxed eddy accumulation (REA) method, TEA does not require the use of proxies and is therefore superior to the indirect REA method. The true eddy accumulation method is by design ideally suited for measuring a wide range of trace gases and other conserved constituents transported with the air. This is because TEA obtains whole air samples and is, in combination with constituent-specific fast or slow analyzers, a universal method for conserved scalars. Despite the recognized value of the method, true eddy accumulation flux measurements remain very challenging to perform as they require fast and dynamic modulation of the air sampling mass flow rate proportional to the magnitude of the instantaneous vertical wind velocity. Appropriate techniques for dynamic mass flow control have long been unavailable, preventing the unlocking of the TEA method's potential for more than 40 years. Recently, a new dynamic and accurate mass flow controller which can resolve turbulence at a frequency of 10 Hz and higher has been developed by the first author. This study presents the proof of concept that practical true eddy accumulation trace gas flux measurements are possible today using dynamic mass flow control, advanced real-time processing of wind measurements, and fully automatic gas handling. We describe setup and methods of the TEA and EC reference flux measurements. The experiment was conducted over grassland and comprised 7 d of continuous flux measurements at 30 min flux integration intervals. The results show that fluxes obtained by TEA compared favorably to EC reference flux measurements, with coefficients of determination of up to 86 % and a slope of 0.98. We present a quantitative analysis of uncertainties of the mass flow control system, the gas analyzer, and gas handling system and their impact on trace gas flux uncertainty, the impact of different approaches to coordinate rotation, and uncertainties of vertical wind velocity measurements. Challenges of TEA are highlighted and solutions presented. The current results are put into the context of previous works. Finally, based on the current successful proof of concept, we suggest specific improvements towards long-term and reliable true eddy accumulation flux measurements.

Field comparison of disjunct and conventional eddy covariance techniques for trace gas flux measurements

2008 ◽  
Vol 152 (3) ◽  
pp. 630-635 ◽  
Author(s):  
J. Rinne ◽  
T. Douffet ◽  
Y. Prigent ◽  
P. Durand
Keyword(s):  
Eddy Covariance ◽  
Trace Gas ◽  
Gas Flux ◽  
Flux Measurements

Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique

2011 ◽  
Vol 116 (D2) ◽  
Author(s):  
Annika Nordbo ◽  
Samuli Launiainen ◽  
Ivan Mammarella ◽  
Matti Leppäranta ◽  
Jussi Huotari ◽  
...  
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Energy Flux ◽  
Eddy Covariance Technique ◽  
Boreal Lake ◽  
Flux Measurements ◽  
Term Energy

scholarly journals Towards standards for measuring greenhouse gas fluxes from agricultural fields using instrumented towers

2006 ◽  
Vol 86 (3) ◽  
pp. 373-400 ◽  
Author(s):  
E. Pattey ◽  
G. Edwards ◽  
I B Strachan ◽  
R L Desjardins ◽  
S. Kaharabata ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Nitrous Oxide ◽  
Greenhouse Gas ◽  
Diode Laser ◽  
Eddy Covariance ◽  
Tunable Diode Laser ◽  
Trace Gas ◽  
Noise Characteristics ◽  
Short Period ◽  
Flux Measurements

This is a discussion of the available technology for measuring turbulent fluxes using instrumented towers. This review focuses on the flux measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) for agricultural systems and the development of standards and protocols for measuring them. Agroecosystems present unique challenges because they undergo large leaf area index (LAI) and canopy architecture changes in a relatively short period of time (i.e., months) coupled with the fact that many of the greenhouse gas sources are diffuse. This review examines all aspects of the theory and application of the micrometeorological techniques, with focus on the flux gradient, eddy accumulation and eddy covariance techniques. Instrument placement, sens or response and noise characteristics are also explored. Innovative applications of micrometeorological methods are discussed for closed- and open-path trace gas sensors and commonly used meteorological instrumentation. The use of fast response single-pass optical tunable diode laser (i.e., CH4, N2O) and infrared gas analyzers (i.e., CO2, H2O) is described. Consideration is also taken of the trace gas sensors’flow system design, mixing ratio measurement, and data acquisition and reduction requirements for micrometeorological flux measurement. Procedures are outlined for the meteorological instrumentation necessary for eddy covariance-based energy budget measurement including ultrasonic anemometry. Key words: Tower-based greenhouse gas flux measurements, nitrous oxide, methane, carbon dioxide, tunable diode laser

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