Determination of the terpene flux from orange species and Norway spruce byrelaxed eddy accumulation

Terpene fluxes from a Norway spruce (Picea abies) forest and an orange orch ard (Citrus clementii and Citrus sinensis) were measured by relaxed eddy ac cumulation (REA) during summer 1997. alpha-pinene and beta-pinene were the most abundant terpenes emitted from Norway spruce and constituted approxima tely 70% of the flux. A much lower flux was observed for myrcene, limonene and gamma-terpinene and both alpha-terpinene and camphor were only occasion ally detected. The average terpene flux was 107.6 ng m(-2) s(-1) which corr esponds to 0.73 mu g g(dw)(-1) h(-1) (30 degrees C) when calculated relativ ely the weight of the dry biomass. The five terpenes which were detected in all samples at the orange orchard were limonene, sabinene, alpha-pinene, t rans-ocimene and beta-pinene with an average Aux of 126.3 ng m(-2) s(-1). C is-ocimene, linalool and myrcene were occasionally detected but no systemat ic upward or downward flux was observed. The results from a laboratory inte rcomparison made in Spain deviated by maximum 7%. The flux measured at the two sites exhibited a strong diurnal variation with maximum in the afternoo n and minimum in the morning hours and evenings. The applied REA system is new in its design and the major advantage is that the air is sampled at a c onstant flow rate on the adsorbent tubes. This is realised by having two pr imary Teflon lines with a relatively large flow rate (61 min(-1)). The air is then sampled from these two Teflon lines on two identical adsorbent tube s at a constant and much lower rate by using two precision pumps operated a t approximately 60 mi min(-1). The terpenes collected on the adsorbent tube s were significantly decomposed by ozone during sampling unless ozone scrub bers were applied. (C) 2000 Elsevier Science Ltd. All rights reserved.