On using radon-222 and CO2 to calculate regional-scale CO2 fluxes

• Main Author: A. I. Hirsch
• Format: Article
• Language: English
• Published: Copernicus Publications 2007-07-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/7/3737/2007/acp-7-3737-2007.pdf

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 <i>F</i> weighted by the sensitivity of the measurements to that flux field, <i>f</i>) 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 <i>F</i> and <i>f</i> 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.