Flux estimates of isoprene, methanol and acetone from airborne PTR-MS measurements over the tropical rainforest during the GABRIEL 2005 campaign
1Max Planck Institute for Chemistry, Air Chemistry, Joh.-Joachim-Becher-Weg 27, 55128 Mainz, Germany
2Research Group Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium
3Department of Environmental Sciences, Wageningen University and Research Centre, Droevendaalsesteeg 4, 6708 PB, Wageningen, The Netherlands
4Faculty of Chemistry, Houari Boumediene University of Science and Technology, BP 32 El-Alia, Bab-Ezzouar 16111, Algiers
Abstract. Tropical forests are a strong source of biogenic volatile organic compounds (BVOCs) to the atmosphere which can potentially impact the atmospheric oxidation capacity. Here we present airborne and ground-based BVOC measurements representative for the long dry season covering a large area of the northern Amazonian rainforest (6–3° N, 50–59° W). The measurements were conducted during the October 2005 GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) campaign. The vertical (35 m to 10 km) and diurnal (09:00–16:00) profiles of isoprene, its oxidation products methacrolein and methyl vinyl ketone and methanol and acetone, measured by PTR-MS (Proton Transfer Reaction Mass Spectrometry), have been used to empirically estimate their emission fluxes from the forest canopy on a regional scale. The mixed layer isoprene emission flux, inferred from the airborne measurements above 300 m, is 5.7 mg isoprene m−2 h−1 after compensating for chemistry and ~6.9 mg isoprene m−2 h−1 taking detrainment into account. This surface flux is in general agreement with previous tropical forest studies. Inferred methanol and acetone emission fluxes are 0.5 mg methanol m−2 h−1 and 0.35 mg acetone m−2 h−1, respectively. The BVOC measurements were compared with fluxes and mixing ratios simulated with a single-column chemistry and climate model (SCM). The inferred isoprene flux is substantially smaller than that simulated with an implementation of a commonly applied BVOC emission algorithm in the SCM.