Direct ecosystem fluxes of volatile organic compounds from oil palms in South-East Asia
1Centre for Ecology & Hydrology, Penicuik, EH26 0QB, UK
2School of Chemistry, University of Edinburgh, EH9 3JJ, UK
3Lancaster Environment Centre, Lancaster University, LA1 4YQ, UK
*currently at: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
**now at: NCAS, School of Earth and Environment, University of Leeds, UK
Abstract. This paper reports the first direct eddy covariance fluxes of reactive biogenic volatile organic compounds (BVOCs) from oil palms to the atmosphere using proton-transfer-reaction mass spectrometry (PTR-MS), measured at a plantation in Malaysian Borneo. At midday, net isoprene flux constituted the largest fraction (84%) of all emitted BVOCs measured, at up to 30 mg m−2 h−1 over 12 days. By contrast, the sum of its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) exhibited clear deposition, with a small average canopy resistance of 230 s m−1. Approximately 15% of the resolved BVOC flux from oil palm trees could be attributed to floral emissions, which are thought to be the largest reported biogenic source of estragole and possibly also toluene. Although on average the midday volume mixing ratio of estragole exceeded that of toluene by almost a factor of two, the corresponding fluxes of these two compounds were nearly the same, amounting to 0.81 and 0.76 mg m−2 h−1, respectively. By fitting the canopy temperature and PAR response of the MEGAN emissions algorithm for isoprene and other emitted BVOCs a basal emission rate of isoprene of 7.8 mg m−2 h−1 was derived. We parameterise fluxes of depositing compounds using a resistance approach using direct canopy measurements of deposition. We propose that it is important to include deposition in flux models, especially for secondary oxidation products, in order to improve flux predictions.