Measurements and quality control of ammonia eddy covariance fluxes: a new strategy for high-frequency attenuation correction

Abstract. Measurements of the surface–atmosphere exchange of ammonia (NH3) are necessary to study the emission and deposition processes of NH3 from managed and natural ecosystems. The eddy covariance technique, which is the most direct method for trace gas exchange measurements at the ecosystem level, requires trace gas detection at a fast sample frequency and high precision. In the past, the major limitation for measuring NH3 eddy covariance fluxes has been the slow time response of NH3 measurements due to NH3 adsorption on instrument surfaces. While high-frequency attenuation correction methods are used, large uncertainties in these corrections still exist, which are mainly due to the lack of understanding of the processes that govern the time response. We measured NH3 fluxes over a corn crop field using a quantum cascade laser spectrometer (QCL) that enables measurements of NH3 at a 10 Hz measurement frequency. The 5-month measurement period covered a large range of environmental conditions that included both periods of NH3 emission and deposition and allowed us to investigate the time response controlling parameters under field conditions. Without high-frequency loss correction, the median daytime NH3 flux was 8.59 ng m−2 s−1 during emission and −19.87 ng m−2 s−1 during deposition periods, with a median daytime random flux error of 1.61 ng m−2 s−1. The overall median flux detection limit was 2.15 ng m−2 s−1, leading to only 11.6 % of valid flux data below the detection limit. From the flux attenuation analysis, we determined a median flux loss of 17 % using the ogive method. No correlations of the flux loss with environmental or analyser parameters (such as humidity or inlet ageing) were found, which was attributed to the uncertainties in the ogive method. Therefore, we propose a new method that simulates the flux loss by using the analyser time response that is determined frequently over the course of the measurement campaign. A correction that uses as a function of the horizontal wind speed and the time response is formulated which accounts for surface ageing and contamination over the course of the experiment. Using this method, the median flux loss was calculated to be 46 %, which was substantially higher than with the ogive method.

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Measurements and quality control of ammonia eddy covariance fluxes: A new strategy for high frequency attenuation correction

10.5194/amt-2019-193 ◽

2019 ◽

Author(s):

Alexander Moravek ◽

Saumya Singh ◽

Elizabeth Pattey ◽

Luc Pelletier ◽

Jennifer G. Murphy

Keyword(s):

Detection Limit ◽

Eddy Covariance ◽

Attenuation Correction ◽

High Frequency ◽

Direct Method ◽

Time Response ◽

Trace Gas ◽

Horizontal Wind ◽

Nh3 Adsorption ◽

Flux Loss

Abstract. Measurements of the surface-atmosphere exchange of ammonia (NH3) are necessary to study the emission and deposition processes of NH3 from managed and natural ecosystems. The eddy covariance technique, which is the most direct method for trace gas exchange measurements at the ecosystem level, requires trace gas detection at fast sample frequency and high precision. In the past, the major limitation for measuring NH3 eddy covariance fluxes has been the slow time response of NH3 measurements due to NH3 adsorption on instrument surfaces. While high frequency attenuation correction methods are used, large uncertainties in these corrections still exist mainly due to the lack of understanding of the processes that govern the time response. We measured NH3 fluxes over a corn crop field using a quantum cascade laser spectrometer (QCL) that enables measurements of NH3 at a 10 Hz measurement frequency. The 5 month measurement period covered a large range of environmental conditions that included both periods of NH3 emission and deposition and allowed us to investigate the time response controlling parameters in field conditions. Without high frequency loss correction, the median daytime NH3 flux was 8.59 ng m−2 s−1 during emission and −19.87 ng m−2 s−1 during deposition periods, with a median daytime random flux error of 1.61 ng m−2 s−1. The overall median flux detection limit was 2.15 ng m−2 s−1, leading to only 11.6 % of valid flux data below the detection limit. From the flux attenuation analysis we determined a median flux loss of 17 % using the ogive method. No correlations of the flux loss with environmental or analyser parameters, such as humidity or inlet aging were found, attributed to the uncertainties in the ogive method. Therefore, we propose a new method that simulates the flux loss by using the analyser time response that is determined frequently over the course of the measurement campaign. A correction that uses as a function of the horizontal wind speed and the time response is formulated which accounts for surface aging and contamination over the course of the experiment. Using this method, the median flux loss was calculated to be 34 %, substantially higher than with the ogive method.

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InnFLUX – an open-source code for conventional and disjunct eddy covariance analysis of trace gas measurements: an urban test case

Atmospheric Measurement Techniques ◽

10.5194/amt-13-1447-2020 ◽

2020 ◽

Vol 13 (3) ◽

pp. 1447-1465 ◽

Cited By ~ 1

Author(s):

Marcus Striednig ◽

Martin Graus ◽

Tilmann D. Märk ◽

Thomas G. Karl

Keyword(s):

Open Source ◽

Eddy Covariance ◽

High Frequency ◽

Urban Canopy ◽

Lag Time ◽

Trace Gas ◽

High Temporal Resolution ◽

Eddy Covariance Method ◽

Wide Range ◽

Gas Measurements

Abstract. We describe and test a new versatile software tool for processing eddy covariance and disjunct eddy covariance flux data. We present an evaluation based on urban non-methane volatile organic compound (NMVOC) measurements using a proton transfer reaction quadrupole interface time-of-flight mass spectrometer (PTR-QiTOF-MS) at the Innsbruck Atmospheric Observatory. The code is based on MATLAB® and can be easily configured to process high-frequency, low-frequency and disjunct data. It can be applied to a wide range of analytical setups for NMVOC and other trace gas measurements, and is tailored towards the application of noisy data, where lag time corrections become challenging. Several corrections and quality control routines are implemented to obtain the most reliable results. The software is open source, so it can be extended and adjusted to specific purposes. We demonstrate the capabilities of the code based on a large urban dataset collected in Innsbruck, Austria, where three-dimensional winds and ambient concentrations of NMVOCs and auxiliary trace gases were sampled with high temporal resolution above an urban canopy. Concomitant measurements of 12C and 13C isotopic NMVOC fluxes allow testing algorithms used for determination of flux limits of detection (LOD) and lag time analysis. We use the high-frequency NMVOC dataset to generate a set of disjunct data and compare these results with the true eddy covariance method. The presented analysis allows testing the theory of disjunct eddy covariance (DEC) in an urban environment. Our findings confirm that the disjunct eddy covariance method can be a reliable tool, even in complex urban environments when fast sensors are not available, but that the increase in random error impedes the ability to detect small fluxes due to higher flux LODs.

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Eddy covariance carbonyl sulphide flux measurements with a quantum cascade laser absorption spectrometer

10.5194/amt-2016-313 ◽

2016 ◽

Author(s):

Katharina Gerdel ◽

Felix M. Spielmann ◽

Albin Hammerle ◽

Georg Wohlfahrt

Keyword(s):

Eddy Covariance ◽

High Frequency ◽

Trace Gas ◽

Quantum Cascade ◽

Laser Absorption ◽

Low Pass ◽

Flux Measurements ◽

Carbonyl Sulphide ◽

High Pass ◽

Processing Steps

Abstract. The trace gas carbonyl sulphide (COS) has lately received growing interest in the eddy covariance (EC) community due to its potential to serve as an independent approach for constraining gross primary production and canopy stomatal conductance. Thanks to recent developments of fast-response high-precision trace gas analysers (e.g. quantum cascade laser absorption spectrometers (QCLAS)), a handful of EC COS flux measurements have been published since 2013. To date, however, a thorough methodological characterisation of QCLAS with regard to the requirements of the EC technique and the necessary processing steps has not been conducted. The objective of this study is to provide for the first time a rigorous analysis of the most widely used QCLAS model for making defensible EC COS flux measurements. Data were collected from May to October 2015 at a temperate mountain grassland in Tyrol, Austria. Analysis of the Allan variance of high-frequency concentration measurements revealed laser drift to occur under field conditions after an averaging time of around 50 s. We thus explored the use of two high-pass filtering approaches (linear detrending and recursive filtering) as opposed to block averaging for covariance computation. Spectral analysis revealed considerable noise at higher frequencies, appearing to influence the high-frequency region of co-spectra (and therefore covariances). By applying a finite-impulse response filter we removed the noise-affected spectral region. The effects of this digital high- and low-pass filtering, and additional low-pass filtering due to the eddy covariance system design, were corrected for using a site-specific reference model co-spectrum and a series of transfer functions. An independent validation of these post-processing steps was achieved by comparison of the CO2 and H2O flux measurements obtained with the QCLAS against those obtained with a closed-path infrared gas analyser. While the validation showed good correspondence and minor statistical differences between the three different high-pass filtering approaches – the benefits of high pass filtering clearly emerged as a reduction of the random flux uncertainty and a higher fraction of data passing the applied QA/QC criterions. We conclude that the most widely used QCLAS can be used to make defensible COS flux measurements provided the appropriate corrections are applied.

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A unified code for conventional and disjunct eddy covariance analysis of trace gas measurements: An urban test case

10.5194/amt-2019-272 ◽

2019 ◽

Author(s):

Marcus Striednig ◽

Martin Graus ◽

Tilmann Märk ◽

Thomas G. Karl

Keyword(s):

Eddy Covariance ◽

High Frequency ◽

Urban Canopy ◽

Lag Time ◽

Trace Gas ◽

High Temporal Resolution ◽

Eddy Covariance Method ◽

Data Set ◽

Wide Range ◽

Gas Measurements

Abstract. We describe and test a new versatile software tool for processing eddy covariance and disjunct eddy covariance data. We present an evaluation based on urban NMVOC measurements using a Proton-transfer-reaction quadrupole interface time of flight mass spectrometer (PTR-QiTOFMS) at the Innsbruck Atmospheric Observatory. The code is based on MATLAB ® and can be easily configured to process high frequency, low frequency and disjunct data. It can be applied to a wide range of analytical setups for NMVOC as well as other trace gas measurements, and is tailored towards the application of noisy data, where lag-time corrections become challenging. Several corrections and quality control routines are implemented to obtain the most reliable results. The software is open-source, so it can be extended and adjusted to specific purposes. We demonstrate the capabilities of the code based on a large urban dataset collected in Innsbruck, Austria, where ambient concentrations of non-methane volatile organic compounds (NMVOC) and auxiliary trace gases were sampled with high temporal resolution above an urban canopy. Concomitant measurements of 12C and 13C isotopic NMVOC fluxes allow testing algorithms used for determinations of flux LODs and lag time analysis. We use the high frequency NMVOC data set to generate a set of disjunct data and compare these results with the true eddy covariance method. The presented analysis allows testing the theory of DEC in an urban environment. Our findings confirm that the disjunct eddy covariance method can be a reliable tool, even in complex urban environments, when fast sensors are not available, but that the increase in random error impedes the ability to detect small fluxes due to higher flux LODs.

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Frequency variations of gravity waves interacting with a time-varying tide

Annales Geophysicae ◽

10.5194/angeo-31-1731-2013 ◽

2013 ◽

Vol 31 (10) ◽

pp. 1731-1743 ◽

Cited By ~ 7

Author(s):

C. M. Huang ◽

S. D. Zhang ◽

F. Yi ◽

K. M. Huang ◽

Y. H. Zhang ◽

...

Keyword(s):

Gravity Waves ◽

High Frequency ◽

Lower Atmosphere ◽

Horizontal Wind ◽

Frequency Variation ◽

Time Varying ◽

Transient Nature ◽

Critical Layers ◽

Favorable Conditions ◽

Frequency Variations

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

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Assessing the Impact of Changes in Land Surface Conditions on WRF Predictions in Arid Regions

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0083.1 ◽

2020 ◽

Vol 21 (12) ◽

pp. 2829-2853 ◽

Cited By ~ 1

Author(s):

Marouane Temimi ◽

Ricardo Fonseca ◽

Narendra Nelli ◽

Michael Weston ◽

Mohan Thota ◽

...

Keyword(s):

Eddy Covariance ◽

Soil Texture ◽

Land Surface ◽

Surface Wind ◽

Surface Fluxes ◽

Abu Dhabi ◽

Horizontal Wind ◽

Cold Bias ◽

Near Surface ◽

The Impact

AbstractA thorough evaluation of the Weather Research and Forecasting (WRF) Model is conducted over the United Arab Emirates, for the period September 2017–August 2018. Two simulations are performed: one with the default model settings (control run), and another one (experiment) with an improved representation of soil texture and land use land cover (LULC). The model predictions are evaluated against observations at 35 weather stations, radiosonde profiles at the coastal Abu Dhabi International Airport, and surface fluxes from eddy-covariance measurements at the inland city of Al Ain. It is found that WRF’s cold temperature bias, also present in the forcing data and seen almost exclusively at night, is reduced when the surface and soil properties are updated, by as much as 3.5 K. This arises from the expansion of the urban areas, and the replacement of loamy regions with sand, which has a higher thermal inertia. However, the model continues to overestimate the strength of the near-surface wind at all stations and seasons, typically by 0.5–1.5 m s−1. It is concluded that the albedo of barren/sparsely vegetated regions in WRF (0.380) is higher than that inferred from eddy-covariance observations (0.340), which can also explain the referred cold bias. At the Abu Dhabi site, even though soil texture and LULC are not changed, there is a small but positive effect on the predicted vertical profiles of temperature, humidity, and horizontal wind speed, mostly between 950 and 750 hPa, possibly because of differences in vertical mixing.

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Photoacoustic spectroscopy for trace gas detection with cryogenic and room-temperature continuous-wave quantum cascade lasers

Open Physics ◽

10.2478/s11534-009-0042-8 ◽

2010 ◽

Vol 8 (2) ◽

Cited By ~ 7

Author(s):

Virginie Zeninari ◽

Agnès Grossel ◽

Lilian Joly ◽

Thomas Decarpenterie ◽

Bruno Grouiez ◽

...

Keyword(s):

Detection Limit ◽

Room Temperature ◽

Quantum Cascade Lasers ◽

Gas Detection ◽

Trace Gas ◽

Atmospheric Gases ◽

Trace Gas Detection ◽

Quantum Cascade ◽

Cascade Lasers

AbstractThe main characteristics that a sensor must possess for trace gas detection and pollution monitoring are high sensitivity, high selectivity and the capability to perform in situ measurements. The photacoustic Helmholtz sensor developed in Reims, used in conjunction with powerful Quantum Cascade Lasers (QCLs), fulfils all these requirements. The best cell response is # 1200 V W−1 cm and the corresponding ultimate sensitivity is j 3.3 × 10−10 W cm−11 Hz−11/2. This efficient sensor is used with mid-infrared QCLs from Alpes Lasers to reach the strong fundamental absorption bands of some atmospheric gases. A first cryogenic QCL emitting at 7.9 μm demonstrates the detection of methane in air with a detection limit of 3 ppb. A detection limit of 20 ppb of NO in air is demonstrated using another cryogenic QCL emitting in the 5.4 μm region. Real in-situ measurements can be achieved only with room-temperature QCLs. A room-temperature QCL emitting in the 7.9 μm region demonstrates the simultaneous detection of methane and nitrous oxide in air (17 and 7 ppb detection limit, respectively). All these reliable measurements allow the estimated detection limit for various atmospheric gases using quantum cascade lasers to be obtained. Each gas absorbing in the infrared may be detected at a detection limit in the ppb or low-ppb range.

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Source partitioning of H<sub>2</sub>O and CO<sub>2</sub> fluxes based on high-frequency eddy covariance data: a comparison between study sites

Biogeosciences ◽

10.5194/bg-16-1111-2019 ◽

2019 ◽

Vol 16 (6) ◽

pp. 1111-1132 ◽

Cited By ~ 5

Author(s):

Anne Klosterhalfen ◽

Alexander Graf ◽

Nicolas Brüggemann ◽

Clemens Drüe ◽

Odilia Esser ◽

...

Keyword(s):

Soil Respiration ◽

Eddy Covariance ◽

High Frequency ◽

Canopy Height ◽

Canopy Density ◽

Partitioning Methods ◽

Site Characteristics ◽

Measurement Height ◽

Study Sites ◽

Source Partitioning

Abstract. For an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H2O and CO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO2 fluxes was less robust than for H2O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration–evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.

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