Obiettivo The degradation of natural nonmethane hydrocarbons (NMHC) (isoprene and terpenes) and formation of peroxides in forest air have been studied.Reliable sampling and determination techniques were developed for the detection of isoprene and monoterpenes. For hydrogen peroxide a previously developed method based on cryosampling and chemiluminescence detection was available. A technique based on the adsorptive preconcentration on 2 adsorbents, combined with an ozone scrubber in front of the sampling tubes was chosen for the measurement of biogenic hydrocarbons. The complexity of the composition of ambient air required the use of a high resolution gas chromatographic analysis coupled with mass spectrometric detection.Several measurement campaigns were carried out at different locations to investigate isoprene and monoterpene concentrations as well as their degradation in and above forests.In addition to the field measurements, Norway spruce saplings were exposed to controlled concentrations of ozone in closed glass chambers to elucidate the influence of ozone, respectively ozone biogenic alkene reaction products, on the monoterpene output of the plant.During ozone fumigation the more reactive monoterpenes d-limonene and beta-phellandrene were found in higher amounts, although a considerable fraction of them was certainly degradated as a consequence of their gas phase reactions.The determination of terpenes in needle tissue from fumigated trees showed results significantly different from those obtained with needles of the control plants. The monoterpene content of current year needles was generally diminished after a fumigation period of about 5 months. Also the amounts of other biogenic hydrocarbons, like sesquiterpenes, diterpenes and oxidized terpenes were reduced in the ozone treated plants. In contrast, recent studies on the monoterpene metabolism investigated in open top chambers have shown no or only slight differences between ozone treated and control plants. Possibly the high air flow through the open top chambers and therfore the low concentrations of products of ozone monoterpene reactions are responsible for these contradictory results.The 2 most widely used techniques for sampling of airborne nonmethane hydrocarbons (NMHC) in remote areas, namely the adsorptive preconcentration on organic polymers or carbon based materials and the whole air sampling in stainless steel canisters, were checked in laboratory studies and field studies regarding their suitability for the collection of unsaturated natural NMHCs, such as isoprene and terpenes.The experiments have shown that ozone scrubbing prior to the preconcentration step is necessary if adsorptive preconcentration is chosen, otherwise an underestimation of some natural alkenes is unavoidable. Concerning grab sampling techniques for biogenic hydrocarbons, an appropriate choice of canister material and a careful deactivation of the sample containers have been found to be an indispensable condition for sampling stability.In addition, results of field measurements in a tropical rain forest were gathered and analysed, indicating the importance of high molecular weight terpenes, like sesquiterpenes, as plant emissions under special environmental conditions. Campo scientifico natural scienceschemical sciencesorganic chemistryhydrocarbonsnatural scienceschemical sciencespolymer sciencesengineering and technologymaterials engineering Programma(i) FP1-ENVPROT 4C - Multiannual research and development programmes (EEC) in the field of the environment - Protection of the environment -, 1986-1990 Argomento(i) Data not available Invito a presentare proposte Data not available Meccanismo di finanziamento CSC - Cost-sharing contracts Coordinatore GESELLSCHAFT ZUR FOERDERUNG DER SPEKTROCHEMIE UND ANGEWANDTEN SPEKTROSKOPIE E .V. Contributo UE Nessun dato Indirizzo Bunsen-Kirchhoff Strasse 11 44139 DORTMUND Germania Mostra sulla mappa Costo totale Nessun dato
