Isoprene and its degradation products methyl vinyl ketone, methacrolein and formaldehyde in a eucalyptus forest during the FIELDVOC'94 campaign in Portugal D. Trapp a, * , K.M. Cooke a,e,1 , H. Fischer a , B. Bonsang b , R.U. Zitzelsberger a,2 , R. Seuwen a , C. Schiller c , T. Zenker a,3 , U. Parchatka a , T.V. Nunes d , C.A. Pio d , A.C. Lewis e , P.W. Seakins e , M.J. Pilling e a Max-Planck-Institut f ur Chemie, Abteilung Chemie der Atmosph are, Postfach 3060, D-55020 Mainz, Germany b Laboratoire des Sciences du Climat et de l'Environnement, CE Saclay, F-91191 Gif-sur-Yvette C edex, France c Department of Chemistry, York University, Keele Street, North York, Ont. Canada M3J 1P3 d Departamento de Ambiente e Ordenamento, Universidade de Aveiro, Campo de Santiago, P-3810 Aveiro, Portugal e School of Chemistry, University of Leeds, Leeds LS2 9JT, UK Received 8 May 1998; received in revised form 24 August 1998; accepted 22 February 2001 Importance of this Paper: The degradation of isoprene under the eect of photochemistry, leads to the formation of carbonyl compounds: mainly formaldehyde, methyl vinyl ketone and methacrolein. The relative abundance of these species depends on the oxidation processes and mainly on the oxidants involved in their production, leading to signi®cant diurnal variations. These yields of formation have been studied from `in situ' measurements during the FIELDVOC'94 campaign in a eucalyptus forest of Portugal. Abstract During FIELDVOC'94, isoprene and its main degradation products, methyl vinyl ketone MVK), methacrolein MAC) and formaldehyde HCHO) were measured in a Portuguese eucalyptus forest. All compounds were analyzed by two or three dierent techniques. Isoprene mixing ratios were highest on sunny days 8 to 12 ppbv) correlating with temperature, and lowest at night <0.02 ppbv). MVK and MAC reached on daytime 1 and 0.5 ppbv, respectively, and minimum values at night, for both species, comprised between 0.1 and 0.2 ppbv. Formaldehyde varied between 1 ppbv night) and 9 ppbv sunny day). Ambient mixing ratios of all compounds were highly variable due to changeable meteorological conditions. The MVK/MAC ratio between 1.5 and 2.5 is indicative of OH-oxidation as the primary isoprene degradation process during the day. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Isoprene; Methyl vinyl ketone; Methacrolein; Formaldehyde; Tropospheric ozone; Eucalyptus forest 1. Introduction Biogenic volatile organic compounds VOCs), espe- cially isoprene, are of increasing interest due to their contribution to the global carbon budget and their po- tential impact on the formation of rural ozone Trainer et al., 1987). They react with the hydroxyl radical OH) Chemosphere ± Global Change Science 3 2001) 295±307 www.elsevier.com/locate/cheglo * Corresponding author. Present address: Granitzer Weg 11, D-24226 Heikendorf, Germany. E-mail address: dtrapp@gmx.de D. Trapp). 1 Present address: Sira Ltd, South Hill, Chislehurst, Kent BR7 5EH, UK 2 Present address: IBM Deutschland, Lyoner Straûe 13, D-60528 Frankfurt, Germany. 3 Present address: NASA Langley Research Centre, Mail Stop 401-A, Hampton, VA 23681, USA. 1465-9972/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S1465-997201)00012-5