Relaxed eddy accumulation method

Schade et al. used PTR-MS to measure in-canopy mixing ratio gradients and abovecanopy fluxes of several VOCs (methanol, acetone, monoterpenes) in a European beech (Fagus sylvatica) forest in Denmark [89]. A relaxed eddy accumulation method was used for the determination of the above-canopy fluxes. The monoterpene emissions and in-canopy mixing ratios showed a diurnal cycle which was found to be consistent with light-dependent emissions, in contrast to temperature-only-driven emissions that had been observed for most conifer species. The measurements also showed that deposition of methanol occurred mostly during the day and that acetone was only emitted once ambient temperatures went above 20°C. 

Graus, M., Hansel, A., Wisthaler, A. et al. (2006) A relaxed-eddy-accumulation method for the measurement of isoprenoid canopy-fluxes using an online gas-chromatographic technique and PTR-MS simultaneously. Atmos. Environ. 40, S43. 

The vertical concentration profiles of biogenic VOCs in a forest canopy were measured, and there were major differences in VOC emission between daytime and nighttime [70,71]. The canopy fluxes of isoprenoids above the Norway spruce forest were determined by GC and PTR-MS with relaxed eddy accumulation (REA) method [72], In the use of REA, samples were analyzed at two different reservoirs, which depended on the direction of the vertical wind w ( up-draught reservoir in case of w > 0 and down-draught reservoir in case of w < 0). Subsequently, the diurnal variation of biogenic VOCs was measured at 12 m (in the treetop) and at 24 m (above the canopy) [73], By using PTR-MS coupled with the eddy covariance technique and GC-flame ionization detector (FID) with a REA system, the mixing ratios and fluxes of total monoterpenes, from a ponderosa pine plantation [74] and from Scots pine... 

Lee et al. used PTR-MS and eddy covariance methods to determine mixing ratios and fluxes of total monoterpenes above a ponderosa pine plantation [34], The results from these studies were compared to those obtained using GC-FID and a relaxed eddy accumulation system. It was found that the daytime measurements resulted in values that agreed well with each other. However, at night PTR-MS detected additional reactive terpenes which... 

EC = Eddy covariance DEC = disjunct eddy covariance vDEC = virtual disjunct eddy covariance REA = relaxed eddy accumulation EM = enclosure method CBL = conveaive boundary layer budgeting MEG = mixed layer gradient MLV = mixed layer variance. 

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