Trace Gas Flux Measurements by the Eddy Correlation Technique: A Time Domain Stability Criterion for Stationarity Tests.

Integrated ecosystem-atmosphere processes studies provide a better understanding how the interacting physical, chemical and biological processes transport and transform energy and matter through the land-atmosphere interface from the cell level to a global scale. To predict the impact of future changes to air quality, climate and ecosystems, there is a need to understand the details of carbon and nitrogen cycling between the terrestrial and atmospheric systems [1]. Diode laser spectroscopy is increasingly being used in atmospheric research [2] and allows the design of chemical species sensors with the time response and sensitivity required for direct eddy correlation flux measurements [3]. For the measurement of the total transport the requirements are less stringent than for the determination of turbulent surface emission and deposition fluxes. For measurements of the turbulent transport the method is rigorous when specific criteria are met. Ideally, the meteorological conditions controlling the state of the turbulence should not vary over the course of the measurement. Since frozen turbulence is assumed, the spatial properties are translated into tempora