A True Eddy Accumulation System for Measuring Trace Gas Flux: Practical Implementation and Evaluation Above a Forest

The true eddy accumulation (TEA) technique for turbulent flux measurements is an alternative to the conventional eddy covariance (EC) technique for measuring trace gases that are difficult to measure by the EC technique. However, the TEA technique has rarely been applied to studies of air–surface gas exchange because of the limited availability of reliable instrumentation. In this study, we developed an air sampling system based on the TEA technique using fast‐response mass flow controllers. The TEA system collects updrafts and downdrafts at sampling flow rates proportional to the vertical wind speed, unless the wind speed exceeds a certain threshold. We evaluated the TEA system above a temperate forest in Japan from May to December 2022 by comparing CO 2 fluxes measured by the TEA system with those measured using EC. The comparison showed a moderate correlation ( R = 0.86) with a small but significant negative bias in the TEA system (2%), likely because of the wind threshold. Our results suggest that the TEA system is a promising alternative for measuring turbulent fluxes of trace gases.