scholarly journals Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

2010 ◽  
Vol 3 (6) ◽  
pp. 1519-1531 ◽  
Author(s):  
B. Tuzson ◽  
R. V. Hiller ◽  
K. Zeyer ◽  
W. Eugster ◽  
A. Neftel ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Best Practice ◽  
Field Evaluation ◽  
Fast Response ◽  
Similar Data ◽  
Mixing Ratios ◽  
Data Treatment ◽  
Sonic Anemometers ◽  
Flux Measurements ◽  
Field Intercomparison

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane exchange. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

scholarly journals Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

2010 ◽  
Vol 3 (4) ◽  
pp. 2961-2993 ◽  
Author(s):  
B. Tuzson ◽  
R. V. Hiller ◽  
K. Zeyer ◽  
W. Eugster ◽  
A. Neftel ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Best Practice ◽  
Field Evaluation ◽  
Methane Flux ◽  
Fast Response ◽  
Similar Data ◽  
Mixing Ratios ◽  
Data Treatment ◽  
Sonic Anemometers ◽  
Flux Measurements

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane flux. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

scholarly journals PTR-TOF-MS eddy covariance measurements of isoprene and monoterpene fluxes from an eastern Amazonian rainforest

2020 ◽  
Vol 20 (12) ◽  
pp. 7179-7191 ◽  
Author(s):  
Chinmoy Sarkar ◽  
Alex B. Guenther ◽  
Jeong-Hoo Park ◽  
Roger Seco ◽  
Eliane Alves ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Atmospheric Chemistry ◽  
Sensible Heat Flux ◽  
Proton Transfer Reaction ◽  
Strongly Correlated ◽  
Mixing Ratios ◽  
Flux Measurements ◽  
Eddy Covariance Measurements ◽  
Emission Models ◽  
Tof Ms

Abstract. Biogenic volatile organic compounds (BVOCs) are important components of the atmosphere due to their contribution to atmospheric chemistry and biogeochemical cycles. Tropical forests are the largest source of the dominant BVOC emissions (e.g. isoprene and monoterpenes). In this study, we report isoprene and total monoterpene flux measurements with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) using the eddy covariance (EC) method at the Tapajós National Forest (2.857∘ S, 54.959∘ W), a primary rainforest in eastern Amazonia. Measurements were carried out from 1 to 16 June 2014, during the wet-to-dry transition season. During the measurement period, the measured daytime (06:00–18:00 LT) average isoprene mixing ratios and fluxes were 1.15±0.60 ppb and 0.55±0.71 mg C m−2 h−1, respectively, whereas the measured daytime average total monoterpene mixing ratios and fluxes were 0.14±0.10 ppb and 0.20±0.25 mg C m−2 h−1, respectively. Midday (10:00–14:00 LT) average isoprene and total monoterpene mixing ratios were 1.70±0.49 and 0.24±0.05 ppb, respectively, whereas midday average isoprene and monoterpene fluxes were 1.24±0.68 and 0.46±0.22 mg C m−2 h−1, respectively. Isoprene and total monoterpene emissions in Tapajós were correlated with ambient temperature and solar radiation. Significant correlation with sensible heat flux, SHF (r2=0.77), was also observed. Measured isoprene and monoterpene fluxes were strongly correlated with each other (r2=0.93). The MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model could simulate most of the observed diurnal variations (r2=0.7 to 0.8) but declined a little later in the evening for both isoprene and total monoterpene fluxes. The results also demonstrate the importance of site-specific vegetation emission factors (EFs) for accurately simulating BVOC fluxes in regional and global BVOC emission models.

scholarly journals Measuring the biosphere-atmosphere exchange of total reactive nitrogen by eddy covariance

2012 ◽  
Vol 9 (11) ◽  
pp. 4247-4261 ◽  
Author(s):  
C. Ammann ◽  
V. Wolff ◽  
O. Marx ◽  
C. Brümmer ◽  
A. Neftel
Keyword(s):  
Eddy Covariance ◽  
Measurement Techniques ◽  
Time Lag ◽  
Fast Response ◽  
Average Concentration ◽  
Reactive Nitrogen ◽  
Gradient Technique ◽  
Measurement Height ◽  
Flux Measurements ◽  
Trace Compounds

Abstract. The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (∑Nr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of ∑Nr and alternating dominance of oxidized (NOX) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19%–26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. ∑Nr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that the main compounds NO2 and NH3 were converted by the TRANC system with an efficiency of near 100%. With an optimised sample inlet also the fluxes of these compounds were recovered reasonably well including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.

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 Nitrous oxide emissions from a commercial cornfield (<i>Zea mays</i>) measured using the eddy-covariance technique

2014 ◽  
Vol 14 (14) ◽  
pp. 20417-20460 ◽  
Author(s):  
H. Huang ◽  
J. Wang ◽  
D. Hui ◽  
D. R. Miller ◽  
S. Bhattarai ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Soil Moisture ◽  
Soil Temperature ◽  
Eddy Covariance ◽  
Growing Season ◽  
Fast Response ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions ◽  
N2o Flux ◽  
Flux Measurements

Abstract. Increases in observed atmospheric concentrations of the long-lived greenhouse gas, nitrous oxide (N2O), have been well documented. However, information on event-related instantaneous emissions during fertilizer applications is lacking. With the development of fast-response N2O analyzers, the eddy covariance (EC) technique can be used to gather instantaneous measurements of N2O concentrations to quantify the exchange of nitrogen between the soil and atmosphere. The objectives of this study were to evaluate the performance of a new EC system, to measure the N2O flux with the system, and finally to examine relationships of the N2O flux with soil temperature, soil moisture, precipitation, and fertilization events. We assembled an EC system that included a sonic anemometer and a fast-response N2O analyzer (quantum cascade laser spectrometer) in a cornfield in Nolensville, Tennessee during the 2012 corn growing season (4 April–8 August). Fertilizer amounts totaling 217 kg N ha−1 were applied to the experimental site. The precision of the instrument was 0.066 ppbv for 10 Hz measurements. The seasonal mean detection limit of the N2O flux measurements was 2.10 ng N m−2 s−1. This EC system can be used to provide reliable N2O flux measurements. The cumulative emitted N2O for the entire growing season was 6.87 kg N2O-N ha−1. The 30 min average N2O emissions ranged from 0 to 11 100 μg N2O{-}N m−2 h−1 (mean = 257.5, standard deviation = 817.7). Average daytime emissions were much higher than night emissions (278.8 ± 865.8 vs. 100.0 ± 210.0 μg N2O-N m−2 h−1). Seasonal fluxes were highly dependent on soil moisture rather than soil temperature, although the diurnal flux was positively related to soil temperature. This study was one of the few experiments that continuously measured instantaneous, high-frequency N2O emissions in crop fields over a growing season of more than 100 days.

scholarly journals Measuring the biosphere-atmosphere exchange of total reactive nitrogen by eddy covariance

2012 ◽  
Vol 9 (6) ◽  
pp. 6857-6898 ◽  
Author(s):  
C. Ammann ◽  
V. Wolff ◽  
O. Marx ◽  
C. Brümmer ◽  
A. Neftel
Keyword(s):  
Eddy Covariance ◽  
Measurement Techniques ◽  
Time Lag ◽  
Fast Response ◽  
Average Concentration ◽  
Reactive Nitrogen ◽  
Gradient Technique ◽  
Measurement Height ◽  
Flux Measurements ◽  
Trace Compounds

Abstract. The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (∑Nr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of ∑Nr and alternating dominance of oxidized (NOx) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19–26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. ∑Nr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that close-to-full conversion of the main compounds NO2 and NH3 was generally obtained by the TRANC system. With an optimised sample inlet also the fluxes of these compounds were recovered fairly including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.

scholarly journals PTR-TOF-MS eddy covariance measurements of isoprene and monoterpene fluxes from an Eastern Amazonian rainforest

2020 ◽  
Author(s):  
Chinmoy Sarkar ◽  
Alex B. Guenther ◽  
Jeong-Hoo Park ◽  
Roger Seco ◽  
Eliane Alves ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Atmospheric Chemistry ◽  
Sensible Heat Flux ◽  
Proton Transfer Reaction ◽  
Strongly Correlated ◽  
Mixing Ratios ◽  
Flux Measurements ◽  
Eddy Covariance Measurements ◽  
Emission Models ◽  
Tof Ms

Abstract. Biogenic volatile organic compounds (BVOCs) are important components of the atmosphere due to their contribution to atmospheric chemistry and biogeochemical cycles. Tropical forests are the largest source of the dominant BVOC emissions (e.g. isoprene and monoterpenes). In this study, we report isoprene and total monoterpene flux measurements with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) using the eddy covariance (EC) method at the Tapajós National Forest (−2.857°S, −54.959°W), a primary rainforest in eastern Amazonia. Measurements were carried out from 1–16 June 2014, during the wet to dry transition season. During the measurement period, the measured daytime (06:00–18:00 LT) average isoprene mixing ratios and fluxes were 1.15 ± 0.60 ppb and 0.55 ± 0.71 mg C m−2 h−1, respectively, whereas the measured daytime average total monoterpenes mixing ratios and fluxes were 0.14 ± 0.10 ppb and 0.20 ± 0.25 mg C m−2 h−1, respectively. Midday (10:00–14:00 LT) average isoprene and total monoterpenes mixing ratios were 1.70 ± 0.49 ppb and 0.24 ± 0.05 ppb, respectively whereas midday average isoprene and monoterpene fluxes were 1.24 ± 0.68 mg C m−2 h−1 and 0.46 ± 0.22 mg C m−2 h−1, respectively. Isoprene and total monoterpene emissions in Tapajós were correlated with ambient temperature and solar radiation. Significant correlation with sensible heat flux, SHF (r2 = 0.77), was also observed. Measured isoprene and monoterpene fluxes were strongly correlated with each other (r2 = 0.93). The MEGAN2.1 model could simulate most of the observed diurnal variations (r2 = 0.7 to 0.8) but declined a little later in the evening for both isoprene and total monoterpene fluxes. The results also demonstrate the importance of site-specific vegetation emission factors (EFs) for accurately simulating BVOC fluxes in regional and global BVOC emission models.

Flux measurements of NHx and NOy with a dual-channel converter above an intensively managed grassland on peat

2021 ◽  
Author(s):  
Pascal Wintjen ◽  
Jeremy Rüffer ◽  
Liv Sokolowsky ◽  
Christof Ammann ◽  
Christian Brümmer
Keyword(s):  
Eddy Covariance ◽  
Nitrogen Saturation ◽  
Organic Fertilizer ◽  
Mineral Fertilizer ◽  
Fast Response ◽  
Reactive Nitrogen ◽  
Nitrogen Compounds ◽  
Northwest Germany ◽  
Flux Measurements ◽  
Intensively Managed

&lt;p&gt;We designed a fast-response two-channel converter called NO&lt;sub&gt;y&lt;/sub&gt;-TRANC for eddy covariance measurements of reduced and oxidized reactive nitrogen compounds (N&lt;sub&gt;r&lt;/sub&gt;). It is a combination of the Total Reactive Atmospheric Nitrogen Converter (TRANC), which converts all reactive forms of nitrogen (&amp;#931;N&lt;sub&gt;r&lt;/sub&gt;), except for nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) and molecular nitrogen (N&lt;sub&gt;2&lt;/sub&gt;), to nitrogen monoxide (NO), and a heated gold catalyst, which converts NO&lt;sub&gt;y&lt;/sub&gt; to NO. NO&lt;sub&gt;x&lt;/sub&gt;, which is the sum of NO and nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;), and higher oxidized nitrogen compounds are described by the term NO&lt;sub&gt;y&lt;/sub&gt;. The NO&lt;sub&gt;y&lt;/sub&gt;-TRANC is coupled to a two-channel chemiluminescence detector (CLD) for measuring NO. Due to a high sampling frequency and a fast response time, the system meets the requirements for flux calculation based on the eddy-covariance method. With this setup, a separation of &amp;#931;N&lt;sub&gt;r&lt;/sub&gt; fluxes in reduced and oxidized nitrogen can be done.&lt;/p&gt;&lt;p&gt;We conducted flux measurements at a typically deeply drained, intensively managed grassland site on peat in an intensive dairy region in Northwest Germany for one year. &amp;#931;N&lt;sub&gt;r&lt;/sub&gt; concentration was 12.4 ppb and NO&lt;sub&gt;y&lt;/sub&gt; concentration was 6.3 ppb on average. We observed mostly emission fluxes at the site after the first fertilization in early spring. The winter month were characterized by slight nitrogen dry deposition. Monthly median of &amp;#931;N&lt;sub&gt;r&lt;/sub&gt; fluxes ranged from -8 to 57 ng N m&lt;sup&gt;-2&lt;/sup&gt;s&lt;sup&gt;-1&lt;/sup&gt; with the exchange being enhanced during summer. We found that &amp;#931;N&lt;sub&gt;r&lt;/sub&gt; and NO&lt;sub&gt;y&lt;/sub&gt; dry emission were comparatively higher under dry conditions, i.e., low air humidity and soil moisture. The emission factors of applied nitrogen after the respective fertilization released as NH&lt;sub&gt;x&lt;/sub&gt; can reach up to 2.0%.&lt;/p&gt;&lt;p&gt;Site management included five fertilization events and five grass cuts. The first fertilization event was at the end of March starting with mineral fertilizer followed by organic fertilizer a week later.&amp;#160; The fertilization scheme was the same for second and third event, but approximately two days were between the application of the fertilizer types. The second fertilization was at the end of May, subsequent fertilizations were done in intervals of 4-5 weeks. Only for the fourth and fifth event, organic fertilizer was used. Organic fertilizer was injected in slits made by v-shaped discs, mineral fertilizer was spread on the soil surface. The emission factor was lower after the first fertilization event compared to events in summer probably indicating a beginning nitrogen saturation after the first fertilization.&lt;/p&gt;&lt;p&gt;Our study demonstrates the application of a novel measurement technique for the determination reactive nitrogen compounds and gives insight into the exchange characteristics of reactive nitrogen under a common agricultural management.&lt;/p&gt;

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.

scholarly journals Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

2014 ◽  
Vol 11 (12) ◽  
pp. 3163-3186 ◽  
Author(s):  
O. Peltola ◽  
A. Hensen ◽  
C. Helfter ◽  
L. Belelli Marchesini ◽  
F. C. Bosveld ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Fast Response ◽  
Quality Data ◽  
External Information ◽  
Closed Path ◽  
Data Logging ◽  
Open Path ◽  
Flux Measurements ◽  
Remote Sites ◽  
Comparison Field

Abstract. The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m−2 s−1, provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m−2 (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were measuring H2O concentrations in addition to CH4, agreed within 3% (355–367 mg (CH4) m−2) and were not clearly different from each other, whereas the other instruments derived total fluxes which showed small but distinct differences (±10%, 330–399 mg (CH4) m−2).

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