Bridging the gap between plot and continental scale: A landscape scale greenhouse gas observation system based on a tall tower eddy covariance.

Due to its urgency, curbing greenhouse gas (GHG) emissions as fast as possible is pivotal for all countries. Mitigation measures are being initiated and a need for monitoring verification and reporting (MVR) of their efficacy arises. Currently existing science based MVR strategies are either too fine scale, e.g. traditional eddy covariance, or very coarse scale, e.g., atmospheric model inversion from high precision continental scale concentration fields. Integral methods to estimate GHG budgets of landscapes and cities are in the state of development. One element of such systems are turbulent flux measurements from tall tower platforms. To be able to document the green transition of Denmark in terms of reducing GHG budgets, we proposed a network of tall tower GHG flux measurements covering representative urban and remote landscapes. In the first step of the project, we designed and built a prototype of such system and applied it in a rural area close to the Danish Capital of Copenhagen.

In this presentation, we define criteria for a successful tall tower based GHG flux observation system for MVR of a change in net GHG emissions. We provide a brief overview how we optimized the design to meet these criteria. Finally, we present some key results from the first five months of continuous observation to demonstrate how well we actually met the criteria with our system and conclude on the future prospects of the proposed tall tower GHG observation network.

The results include net fluxes of all major long living GHG (CO₂, CH₄ and N₂O) and two indicator gasses, i.e. carbonyl sulfide (COS) and carbon monoxide (CO). These indicator gases were chosen to represent photosynthesis and to estimate fossil CO₂ fluxes from combustion processes. Important results are how accurate the data represent the landscape and what the detection limits for flux estimations of the different GHGs are.