VOC emissions from Norway spruce (Picea abies L. [Karst]) twigs in the field—Results of a dynamic enclosure study

During the 2002 summer intensive field campaign of BEWA2000 a proton-transfer-reaction mass spectrometer (PTR-MS) was used for online determination of volatile organic compounds (VOC) emitted by Norway spruce (Picea abies L. [Karst]) twigs in a dynamic sampling enclosure. Emissions of isoprenoids (isoprene and monoterpenes) and oxygenated VOC (OVOC; acetaldehyde, acetone, methanol, and ethanol) were investigated. Emissions showed clear diurnal patterns with high daytime emission rates amounting to 1.8 μg C g−1 dwt h−1 for the sum of monoterpenes and in the range of 0.1 to 0.6 μg C g−1 dwt h−1 for isoprene>acetone>ethanol>methanol. Data were used to validate existing models on isoprene and monoterpene emissions and to discuss environmental and physiological factors affecting VOC emissions. Isoprene and acetaldehyde emission rates were best modelled applying the Guenther 1993 temperature and solar radiation algorithm. Emissions of monoterpenes, acetone and ethanol were best described by a temperature-only exponential algorithm. Using these model approaches a maximum emission variability of 66% was covered (isoprene). Poor r2 values ranging from 0.15 to 0.42 were typical for oxygenated VOC emission modelling indicating the need for model improvement e.g. development of process-based models describing the emission as a result of biochemical de novo synthesis as well as physico-chemical transport properties inside the leaves.