Choosing an optimal β factor for relaxed eddy accumulation applications across vegetated and non-vegetated surfaces

<p>Understanding the source and transport behavior of atmospheric trace gases is important to better quantify, predict, and mitigate anthropogenic effects on the environment and climate. The relaxed eddy accumulation (REA) method enables measuring the fluxes of atmospheric compounds for which fast-response sensors are not available. In REA applications, air is sampled depending on the direction of the vertical wind w, into a reservoir for updrafts, and a reservoir for downdrafts, respectively. Deadbands are used to select only certain turbulent motions during sampling to obtain the concentration difference. The <em>&#946;</em> factor is used to scale the measured concentration difference between both reservoirs to the flux.</p> <p>In this study, we evaluated a variety of different REA approaches with the goal of formulating recommendations applicable over a wide range of surfaces and meteorological conditions for an optimal choice of the <em>&#946;</em> factor in combination with a suitable deadband. Observations with fast-response sensors were collected in three contrasting ecosystems offering stark differences in scalar transport and dynamics: a mid-latitude grassland ecosystem in Europe (Lindenberg, Germany), a loose gravel surface of the Dry Valleys of Antarctica, and a spruce forest site in the European mid-range mountains (Waldstein, Germany). REA applications were simulated using the high-frequency observations.</p>