Eddy Covariance Measuring Methodologies

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 

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. 

Spirig et al. have reported PTR-MS measurements taken in a mixed deciduous forest in north-west Germany coupled to eddy covariance methodology for the determination of biogenic VOC fluxes [82], Fluxes for isoprene and the monoterpenes were shown to be consistent with light and temperature dependent emissions of these compounds. Average daytime emissions of methanol, isoprene and monoterpenes were determined to be 0.087 pg s 0.94 pg s and 0.3 pg m s respectively. 

Rinne et al. used PTR-MS with a disjunct eddy covariance method to measure the fluxes of methanol, acetaldehyde and monoterpenes above a Scots pine (Pirns sylvestris) forest in Finland [90]. Chemical modeling showed that there was little loss owing to reaction and that the VOC fluxes followed the traditional exponential temperature-dependent emission 

Karl et al. tested a virtual disjunct eddy covariance device with field measurements of biogenic VOC fluxes at a subalpine forest site in the Rocky Mountains of the United States [84], where a short grazing season is only possible owing to the altitude. Significant fluxes of MBO, methanol, acetone and acetaldehyde were observed. 

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PTR-MS in the Environmental Sciences 147 5.3.2.4 Eddy Covariance Measuring Methodologies... 

Table 5.2 provides a summary of the environments in which eddy covariance measurements of VOC fluxes using PTR-MS have been made. For convenience and for completeness other methodologies for determining biogenic flux using PTR-MS and ecosystem types other than forests, such as alfalfa fields [81], are included in the table. 

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