Tube transport of water vapor with condensation and desorption

Nordbo, Annika; Kekäläinen, Pekka; Siivola, Erkki; Lehto, Roope; Vesala, Timo; Timonen, J.

doi:10.1063/1.4804639

Cited by 10 publications

(4 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The nal delay was calculated by Eq. 1 and is highlighted in the development of humidity, but also to the wall material (Bloom et al, 1980), its age, and to the presence of aerosols (Mammarella et al, 2009;Nordbo et al, 2013). Humidity also has an eect on the lag of the measured χ CO 2 , although in an attenuated form, due to solubility in water.…”

Section: Raw Data Processing Diagnosticsmentioning

confidence: 99%

High-Resolution Vertical Profile Measurements for Carbon Dioxide and Water Vapour Concentrations Within and Above Crop Canopies

Ney

Graf

2017

Boundary-Layer Meteorol

View full text Add to dashboard Cite

We present a portable elevator-based facility for measuring CO 2 , water vapour, temperature and wind-speed proles between the soil surface and the atmospheric surface layer above crop canopies. The end of a tube connected to a closed-path gas analyzer is continuously moved up and down over the prole range (in our case, approximately 2 m) while concentrations are logged at a frequency of 20 s −1. Using campaign measurements in winter wheat, winter barley and a catch crop mixture (spring 2015 to autumn 2016) during dierent stages of crop development and dierent times of the day, we demonstrate a simple approach to correct for time lags, and the resulting proles of 30-min mean mole fractions of CO 2 and H 2 O over height increments of 0.025 m. The proles clearly show the eects of soil respiration and photosynthetic carbon assimilation, varying both during the diurnal cycle and during the growing season. Proles of temperature and wind speed are based on a ventilated newire thermocouple and a hot-wire anemometer, respectively. Measurements over bare soil and a short plant canopy were analyzed in the framework of Monin-Obukhov similarity theory to check the validity of the measurements and raw-data-processing approach. Derived uxes of CO 2 , latent and sensible heat and momentum show good agreement with eddycovariance measurements.

show abstract

Section: Raw Data Processing Diagnosticsmentioning

confidence: 99%

High-Resolution Vertical Profile Measurements for Carbon Dioxide and Water Vapour Concentrations Within and Above Crop Canopies

Ney

Graf

2017

Boundary-Layer Meteorol

View full text Add to dashboard Cite

show abstract

“…To date a comprehensive explanation for the amplitude and phase shifts is missing. However, Nordbo et al (2013) showed promising development in this respect.…”

Section: Using External H 2 O In Correcting Ch 4 Fluxesmentioning

confidence: 99%

“…Adsorption/desorption of H 2 O molecules on the sampling tube walls and filters (closed-path gas analysers only) cause amplitude and phase shifts compared to an unperturbed, ideal signal (Fratini et al, 2012;Ibrom et al, 2007a;Mammarella et al, 2009;Massman and Ibrom, 2008;Nordbo et al, 2013;Runkle et al, 2012). Thus, H 2 O lag times tend to be longer than for other gases in the same sampling tube and attenuations of H 2 O fluctuations are enhanced.…”

Section: Using External H 2 O In Correcting Ch 4 Fluxesmentioning

confidence: 99%

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

et al. 2014

View full text Add to dashboard Cite

Abstract. The performance of eight fast-response methane (CH 4 ) 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 CH 4 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 CH 4 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 H 2 O concentrations alongside CH 4 (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 H 2 O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH 4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH 4 ) m −2 (8 % of the measured mean flux) in the processed and corrected CH 4 fluxes on a monthly scale due to missing H 2 O concentration measurements. Finally, cumulative CH 4 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 H 2 O concentrations in addition to CH 4 , agreed within 3 % (355-367 mg (CH 4 ) 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 (CH 4 ) m −2 ).Published by Copernicus Publications on behalf of the European Geosciences Union. 3164O. Peltola et al.: Evaluating the performance of gas analysers for CH 4 EC flux measurements

show abstract

“…This is due to adsorption and desorption of H 2 O to sampling tube walls, a process which cannot be described accurately with Eq. (3) (Nordbo et al, 2013). Hence different transfer functions have been proposed for H 2 O (De Ligne et al, 2010;Nordbo et al, 2014).…”

Section: Co 2 and H 2 O Fluxes Corrected With The Four Methodsmentioning

confidence: 99%

The high-frequency response correction of eddy covariance fluxes – Part 1: An experimental approach and its interdependence with the time-lag estimation

et al. 2021

View full text Add to dashboard Cite

Abstract. The eddy covariance (EC) technique has emerged as the prevailing method to observe the ecosystem–atmosphere exchange of gases, heat and momentum. EC measurements require rigorous data processing to derive the fluxes that can be used to analyse exchange processes at the ecosystem–atmosphere interface. Here we show that two common post-processing steps (time-lag estimation via cross-covariance maximisation and correction for limited frequency response of the EC measurement system) are interrelated, and this should be accounted for when processing EC gas flux data. These findings are applicable to EC systems employing closed- or enclosed-path gas analysers which can be approximated to be linear first-order sensors. These EC measurement systems act as low-pass filters on the time series of the scalar χ (e.g. CO2, H2O), and this induces a time lag (tlpf) between vertical wind speed (w) and scalar χ time series which is additional to the travel time of the gas signal in the sampling line (tube, filters). Time-lag estimation via cross-covariance maximisation inadvertently accounts also for tlpf and hence overestimates the travel time in the sampling line. This results in a phase shift between the time series of w and χ, which distorts the measured cospectra between w and χ and hence has an effect on the correction for the dampening of the EC flux signal at high frequencies. This distortion can be described with a transfer function related to the phase shift (Hp) which is typically neglected when processing EC flux data. Based on analyses using EC data from two contrasting measurement sites, we show that the low-pass-filtering-induced time lag increases approximately linearly with the time constant of the low-pass filter, and hence the importance of Hp in describing the high-frequency flux loss increases as well. Incomplete description of these processes in EC data processing algorithms results in flux biases of up to 10 %, with the largest biases observed for short towers due to the prevalence of small-scale turbulence. Based on these findings, it is suggested that spectral correction methods implemented in EC data processing algorithms are revised to account for the influence of low-pass-filtering-induced time lag.

show abstract

Tube transport of water vapor with condensation and desorption

Cited by 10 publications

References 25 publications

High-Resolution Vertical Profile Measurements for Carbon Dioxide and Water Vapour Concentrations Within and Above Crop Canopies

High-Resolution Vertical Profile Measurements for Carbon Dioxide and Water Vapour Concentrations Within and Above Crop Canopies

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

The high-frequency response correction of eddy covariance fluxes – Part 1: An experimental approach and its interdependence with the time-lag estimation

Contact Info

Product

Resources

About