Abstract
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 of 1 mg m−2 h−1, 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. Consistent with Karl et al. (2010), we also propose that it is important to include deposition in flux models, especially for secondary oxidation products, in order to improve flux predictions.
Highlights
Emissions of biogenic volatile organic compounds (BVOCs) constitute approximately 90 % of all atmospheric volatile organic compounds (VOCs), half of which are contributed by one compound – isoprene, which has an estimated global annual emission from vegetation of ∼ 600 Tg (Guenther et al, 2006)
This paper reports the first direct eddy covariance fluxes of reactive biogenic volatile organic compounds (BVOCs) from oil palms to the atmosphere using protontransfer-reaction mass spectrometry (PTR-MS), measured at a plantation in Malaysian Borneo
There are practically no VOC emission data for South East Asia, an area currently undergoing widespread and rapid land-use change where land that was once rainforest is occupied by oil palm plantations (Elaeis guineensis)
Summary
Emissions of biogenic volatile organic compounds (BVOCs) constitute approximately 90 % of all atmospheric volatile organic compounds (VOCs), half of which are contributed by one compound – isoprene, which has an estimated global annual emission from vegetation of ∼ 600 Tg (Guenther et al, 2006). VOCs play many important roles in atmospheric chemistry, for example serving as sinks for OH radicals, and indirectly prolonging the lifetime of pollutants and greenhouse gases in the troposphere. They contribute to the formation of tropospheric ozone and secondary organic aerosol, and indirectly affect regional and global climate. Representation of VOCs in current models has high uncertainties because of the limited number of measurements, in the tropical regions which are thought to contribute half of the global VOC emissions (Karl et al, 2004). It has only recently been found that oil palms are very high isoprene emitters (Wilkinson et al, 2006; Owen and Penuelas, 2005; Geron et al, 2006)
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