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This paper reports the fluxes and mixing ratios of biogenically emitted\udvolatile organic compounds (BVOCs) 4 m above a mixed oak and hornbeam forest\udin northern Italy. Fluxes of methanol, acetaldehyde, isoprene, methyl vinyl\udketone + methacrolein, methyl ethyl ketone and monoterpenes were obtained\udusing both a proton-transfer-reaction mass spectrometer (PTR-MS) and a\udproton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS)\udtogether with the methods of virtual disjunct eddy covariance (using PTR-MS) and\udeddy covariance (using PTR-ToF-MS). Isoprene was the dominant emitted compound\udwith a mean daytime flux of 1.9 mg m−2 h−1. Mixing ratios,\udrecorded 4 m above the canopy, were dominated by methanol with a mean value\udof 6.2 ppbv over the 28-day measurement period. Comparison of isoprene\udfluxes calculated using the PTR-MS and PTR-ToF-MS showed very good agreement\udwhile comparison of the monoterpene fluxes suggested a slight over\udestimation of the flux by the PTR-MS. A basal isoprene emission rate for the\udforest of 1.7 mg m−2 h−1 was calculated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) isoprene\udemission algorithms (Guenther et al., 2006). A detailed tree-species\uddistribution map for the site enabled the leaf-level emission of isoprene\udand monoterpenes recorded using gas-chromatography mass spectrometry (GC–MS) to be scaled up to produce a\udbottom-up canopy-scale flux. This was compared with the top-down\udcanopy-scale flux obtained by measurements. For monoterpenes, the two\udestimates were closely correlated and this correlation improved when the\udplant-species composition in the individual flux footprint was taken into\udaccount. However, the bottom-up approach significantly underestimated the\udisoprene flux, compared with the top-down measurements, suggesting that the\udleaf-level measurements were not representative of actual emission rates

Canopy-scale flux measurements and bottom-up emission estimates of volatile organic compounds from a mixed oak and hornbeam forest in northern Italy