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Inferring 222Rn soil fluxes from ambient 222Rn activity and eddy covariance measurements of CO2

Van Der Laan, Sander; Manohar, Swagath; Vermeulen, Alex LU ; Bosveld, Fred; Meijer, Harro; Manning, Andrew; Van Der Molen, Michiel and Van Der Laan-Luijkx, Ingrid (2016) In Atmospheric Measurement Techniques 9(11). p.5523-5533
Abstract

We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC), to estimate regional-scale surface fluxes of 222Rn from tower-based observations of 222Rn activity concentration, CO2 mole fractions and direct CO2 flux measurements from eddy covariance. For specific events, the regional (222Rn) surface flux is calculated from short-term changes in ambient (222Rn) activity concentration scaled by the ratio of the mean CO2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels) and space (i.e. over the footprint of the observations).... (More)

We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC), to estimate regional-scale surface fluxes of 222Rn from tower-based observations of 222Rn activity concentration, CO2 mole fractions and direct CO2 flux measurements from eddy covariance. For specific events, the regional (222Rn) surface flux is calculated from short-term changes in ambient (222Rn) activity concentration scaled by the ratio of the mean CO2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels) and space (i.e. over the footprint of the observations). The measurement uncertainty obtained is about ±15 % for diurnal events and about ±10 % for longer-term (e.g. seasonal or annual) means. The method does not provide continuous observations, but reliable daily averages can be obtained. We applied our method to in situ observations from two sites in the Netherlands: Cabauw station (CBW) and Lutjewad station (LUT). For LUT, which is an intensive agricultural site, we estimated a mean 222Rn surface flux of (0.29±0.02)atomscm-2s-1 with values > 0.5atomscm-2s-1 to the south and south-east. For CBW we estimated a mean 222Rn surface flux of (0.63±0.04)atomscm-2s-1. The highest values were observed to the south-west, where the soil type is mainly river clay. For both stations good agreement was found between our results and those from measurements with soil chambers and two recently published 222Rn soil flux maps for Europe. At both sites, large spatial and temporal variability of 222Rn surface fluxes were observed which would be impractical to measure with a soil chamber. SPOT-EC, therefore, offers an important new tool for estimating regional-scale 222Rn surface fluxes. Practical applications furthermore include calibration of process-based 222Rn soil flux models, validation of atmospheric transport models and performing regional-scale inversions, e.g. of greenhouse gases via the SPOT 222Rn-tracer method.

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organization
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type
Contribution to journal
publication status
published
subject
in
Atmospheric Measurement Techniques
volume
9
issue
11
pages
11 pages
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • scopus:84999854382
ISSN
1867-1381
DOI
10.5194/amt-9-5523-2016
language
English
LU publication?
yes
id
04b1d3cb-0c48-4b3b-b3b9-80454744d37f
date added to LUP
2016-12-19 12:39:26
date last changed
2017-10-08 04:56:15
@article{04b1d3cb-0c48-4b3b-b3b9-80454744d37f,
  abstract     = {<p>We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC), to estimate regional-scale surface fluxes of 222Rn from tower-based observations of 222Rn activity concentration, CO2 mole fractions and direct CO2 flux measurements from eddy covariance. For specific events, the regional (222Rn) surface flux is calculated from short-term changes in ambient (222Rn) activity concentration scaled by the ratio of the mean CO2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels) and space (i.e. over the footprint of the observations). The measurement uncertainty obtained is about ±15 % for diurnal events and about ±10 % for longer-term (e.g. seasonal or annual) means. The method does not provide continuous observations, but reliable daily averages can be obtained. We applied our method to in situ observations from two sites in the Netherlands: Cabauw station (CBW) and Lutjewad station (LUT). For LUT, which is an intensive agricultural site, we estimated a mean 222Rn surface flux of (0.29±0.02)atomscm-2s-1 with values &amp;gt; 0.5atomscm-2s-1 to the south and south-east. For CBW we estimated a mean 222Rn surface flux of (0.63±0.04)atomscm-2s-1. The highest values were observed to the south-west, where the soil type is mainly river clay. For both stations good agreement was found between our results and those from measurements with soil chambers and two recently published 222Rn soil flux maps for Europe. At both sites, large spatial and temporal variability of 222Rn surface fluxes were observed which would be impractical to measure with a soil chamber. SPOT-EC, therefore, offers an important new tool for estimating regional-scale 222Rn surface fluxes. Practical applications furthermore include calibration of process-based 222Rn soil flux models, validation of atmospheric transport models and performing regional-scale inversions, e.g. of greenhouse gases via the SPOT 222Rn-tracer method.</p>},
  author       = {Van Der Laan, Sander and Manohar, Swagath and Vermeulen, Alex and Bosveld, Fred and Meijer, Harro and Manning, Andrew and Van Der Molen, Michiel and Van Der Laan-Luijkx, Ingrid},
  issn         = {1867-1381},
  language     = {eng},
  month        = {11},
  number       = {11},
  pages        = {5523--5533},
  publisher    = {Copernicus Gesellschaft Mbh},
  series       = {Atmospheric Measurement Techniques},
  title        = {Inferring 222Rn soil fluxes from ambient 222Rn activity and eddy covariance measurements of CO2},
  url          = {http://dx.doi.org/10.5194/amt-9-5523-2016},
  volume       = {9},
  year         = {2016},
}