Biogeosciences
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4
5
2007
10.5194/bg-4-715-2007
http://www.biogeosciences.net/4/715/2007/
http://www.biogeosciences.net/4/715/2007/bg-4-715-2007.html
http://www.biogeosciences.net/4/715/2007/bg-4-715-2007.pdf
715
728
2007-08-31
Suitability of quantum cascade laser spectroscopy for CH<sub>4</sub> and N<sub>2</sub>O eddy covariance flux measurements
P. S. Kroon
p.kroon@ecn.nl
A. Hensen
H. J. J. Jonker
M. S. Zahniser
W. H. van 't Veen
A. T. Vermeulen
Energy Research Centre of the Netherlands (ECN), Department of Air Quality and Climate Change, The Netherlands
TU Delft, Department of Multi-Scale Physics, Research Group Clouds, Climate and Air Quality, The Netherlands
Aerodyne Research, Inc., USA
A quantum cascade laser spectrometer was evaluated for eddy covariance flux
measurements of CH<sub>4</sub> and N<sub>2</sub>O using three months of continuous
measurements at a field site. The required criteria for eddy covariance flux
measurements including continuity, sampling frequency, precision and
stationarity were examined. The system operated continuously at a dairy farm
on peat grassland in the Netherlands from 17 August to 6 November 2006.
An automatic liquid nitrogen filling system for the infrared detector was
employed to provide unattended operation of the system. The electronic
sampling frequency was 10 Hz, however, the flow response time was
0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of
2.9 and 0.5 ppb Hz<sup>−1/2</sup> was obtained for CH<sub>4</sub> and N<sub>2</sub>O,
respectively. Accuracy was assured by frequent calibrations using low and
high standard additions. Drifts in the system were compensated by using a
120 s running mean filter. The average CH<sub>4</sub> and N<sub>2</sub>O
exchange was 512 ngC m<sup>−2</sup> s<sup>−1</sup> (2.46 mg m<sup>−2</sup> hr<sup>−1</sup>) and
52 ngN m<sup>−2</sup> s<sup>−1</sup> (0.29 mg m<sup>−2</sup> hr<sup>−1</sup>). Given that 40% of
the total N<sub>2</sub>O emission was due to a fertilizing event.
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