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

Abstract

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

Air–sea fluxes of CO<sub>2</sub> and CH<sub>4</sub> from the Penlee Point Atmospheric Observatory on the south-west coast of the UK

“…more variable C CH 4 ), the flux uncertainty increases substantially and becomes much greater than F CH 4 , while the relative importance of σ 2 C n decreases. Thus, we expect the 10-fold greater CH 4 flux detection limit estimated by Peltola et al (2014) to be due to the higher variability in C CH 4 over land than at our marine site (for onshore winds only). Over the open ocean where σ C a in CH 4 is likely to be even lower than at PPAO, the flux detection limit for CH 4 should slightly decrease.…”

Improvement of vertical velocity statistics measured by a Doppler lidar through comparison with sonic anemometer observations

“…Grund et al, 2001), and it was also extended to correct eddy-covariance flux measurements of trace gases (e.g. Mauder et al, 2013;Peltola et al, 2014). This technique has been used to study higher-order statistics in the convective boundary layer (e.g.…”

Quantifying the uncertainty of eddy covariance fluxes due to the use of different software packages and combinations of processing steps in two contrasting ecosystems

“…Nowadays, new and better instrumentation is available for measuring turbulent fluxes of energy and matter using the EC technique. Recent studies have compared commercially available gas analysers, focusing on precision, stability and systematic and random errors both for CO 2 fluxes (Burba et al, 2008;Ibrom et al, 2007a;Järvi et al, 2009) and methane (CH 4 ) and nitrous oxide (N 2 O) fluxes (Detto et al, 2011;Peltola et al, 2013Peltola et al, , 2014Rannik et al, 2015). However, only a few studies have reported an inter-comparison between EC software packages, and all focusing only on energy and CO 2 fluxes (Fratini and Mauder, 2014;Mauder et al, 2007Mauder et al, , 2008.…”