Alternative Turbulent Trace Gas Flux Measurement Methods

The eddy-covariance (EC) method is the most direct micrometeorological approach to measure the surface–atmosphere trace gases under turbulent conditions. The measurement of trace gas fluxes by eddy covariance requires fast-response instruments (higher than 1 Hz) to measure the turbulent fluctuations of vertical wind velocity and trace gas mixing ratio. For many trace gas species, such fast response analyzers are either not available or do not meet the required precision, long-term stability, and ease of operation under field conditions.Thus, a range of alternative flux measurement techniques have been developed to relax the requirement for fast response time and precision of analysis of the targeted trace gases. These alternative trace gas flux measurement methods are based on surface layer gradients, eddy accumulation, and disjunct eddy-covariance approaches. Of these, the two latter are presented in this chapter. In addition, the surface layer renewal approach,
which can be used to understand turbulent exchange processes, and the nocturnal boundary layer Keeling plot approach for determination of the isotopic composition of emitted gases under stable conditions are also described.