Regional CO2 Fluxes Using a Network of Carbon Dioxide Mixing Ratio Sensors

Inverse studies of CO₂ mixing ratio are traditionally conducted at coarse spatial and temporal resolution. This limits our ability to evaluate efforts to upscale chamber and stand level CO₂ flux measurements to regional scales, where coherent climate and ecosystem mechanisms govern the carbon cycle. We present an effort to implement atmospheric budget or inversion methodology on a regional scale. A first step towards this end is the evaluation of a network of six relatively inexpensive CO₂ mixing ratio measurement systems deployed on towers in northern Wisconsin as part of the Chequamegon Ecosystem-Atmosphere Study. Five systems are distributed on a circle of roughly 150-km radius, while one system is centrally located. All measurements are taken at a height of 76 m. The systems use LiCor-820 infrared CO₂ analyzers and are calibrated every two hours using four samples known to within +/- 0.05 ppm CO₂. Field tests prior to deployment in which the six systems sampled the same air indicate agreement of the systems to within 0.5--1.0 ppm from the mean during relatively quiescent periods. Tests using tanks containing known CO₂ concentrations exhibit standard deviations of 1.0 ppm or less. If network precision and accuracy prove to be sufficiently high, these data will detect horizontal gradients in CO₂ mixing ratios caused by net ecosystem-atmosphere exchange. These horizontal gradients will be the basis for using atmospheric budget methods to derive regional fluxes with spatial and temporal resolution fine enough to warrant comparison to the ChEAS regional flux tower network. Results from the deployment (July--October 2003) are presented.