THE DETERMINATION OF TERPENES IN FOREST AIR

Monoterpene emissions are an important source of hydrocarbons in the atmosphere. An analytical method was developed and validated to determine the monoterpene concentrations at different heights above the canopy of a forest. The method focused on alpha- and beta-pinene, 3-carene and limonene. The detection limits for these compounds were ca. 0.05 ng and the repeatability ca. 5% (with the exception of limonene which showed a repeatability of ca. 15%). The breakthroug volumes for all four terpenes were > 3 l. The presence of realistic concentrations of O3, NO2 and H2O during sampling resulted in a decrease of 10-50% of the amounts of recovered terpenes. The method was used in a pilot experiment to determine the concentrations of the monoterpenes at different heights above a pine forest. The concentrations of the measured terpenes varied from < 0.05 to 1.6 ng l-1, with alpha- and beta-pinene being the most prominent. A concentration gradient could be determined for alpha- and beta-pinene and 3-carene.