Atmos. Chem. Phys. Discuss., 6, 10929-10958, 2006
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On using radon-222 and CO2 to calculate regional-scale CO2 fluxes
A. I. Hirsch
1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
2NOAA/ESRL Global Monitoring Division, Boulder, Colorado, USA

Abstract. Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.

Citation: Hirsch, A. I.: On using radon-222 and CO2 to calculate regional-scale CO2 fluxes, Atmos. Chem. Phys. Discuss., 6, 10929-10958, doi:10.5194/acpd-6-10929-2006, 2006.
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