Eddy covariance flux measurements of biogenic VOCs during ECHO 2003 using proton transfer reaction mass spectrometry

Abstract

Abstract. Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. The eddy covariance (EC) technique was applied since it represents the most direct flux measurement approach on the canopy scale and is, therefore, least susceptible to these non-ideal conditions. A specific flux calculation method was used to account for the sequential multi-component PTR-MS measurements and allowing an individual delay time adjustment as well as a rigorous quality control based on cospectral analysis. The validated flux results are consistent with light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average daytime emissions of 0.94 and 0.3 µg m −2 s −1 , respectively. Emissions of methanol reached on average 0.087 µg m −2 s −1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.

History effect of light and temperature on monoterpenoid emissions from Fagus sylvatica L.

“…This light and temperature dependence of monoterpene emissions by F. sylvatica L., with emissions close to zero at darkness, is in agreement with what has been reported previously by several authors (Schuh et al, 1997;Spirig et al, 2005;Holzke et al, 2006;Moukhtar et al, 2005;Dindorf et al, 2006). In the beginning and at the end of the experimental period the emission rate at zero PPFD was found to be negligible.…”

“…(2)) inferred from the measured monoterpenoid emission rates of the second tree are found to vary between 100 and 1550 mg m À2 h À1 or 2 and 32 mg g DW À1 h À1 , in good agreement with literature data reported for F. sylvatica L. in recent years (Schuh et al, 1997;Kahl et al, 1999;Spirig et al, 2005;Moukhtar et al, 2005;Dindorf et al, 2006), which have been recently compiled in Table 3 of Dindorf et al (2006), and with the values adopted in the two most recent European plant-specific BVOC inventories, 22.1 mg g DW À1 h À1 (Karl et al, 2009) and 10.0 mg g DW À1 h À1 (Schurgers et al, 2009). …”

Observations of Diurnal to Weekly Variations of Monoterpene-Dominated Fluxes of Volatile Organic Compounds from Mediterranean Forests: Implications for Regional Modeling

“…26,27 Quality assurance of the fluxes was performed by removing data that failed the criteria for turbulence (friction velocity below 0.15 m s −1 ) or stationarity (when the stationarity test, calculated on 5 min subperiods, for the various BVOC fluxes exceeded 60% as defined by Foken and Wichura 28 ). In total, also including instrument failures, we gap-filled about 60% of the data set, mainly during the night hours.…”

Deposition fluxes of terpenes over grassland

“…Forests emit large quantities of monoterpenes. For example average daytime monoterpene emissions of 2.2 nmol m −2 s −1 were reported for a mixed deciduous forest [Spirig et al, 2005]. During warm days, Grabmer et al [2004] reported monoterpene emission fluxes up to 2.5 nmol m −2 s −1 over a Norway Spruce forest using the relaxed eddy covariance method.…”