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The vertical distribution of ambient biogenic volatile organic compounds(BVOC) concentrations within a hemiboreal forest canopy was investigated overa period of one year. Variability in temporal and spatial isopreneconcentrations, ranging from 0.1 to 7.5 μg m−3, can be mainlyexplained by biogenic emissions from deciduous trees. Monoterpeneconcentrations exceeded isoprene largely and ranged from 0.01 to140 μg m−3 and during winter time anthropogenic contributionsare likely. Variation in monoterpene concentrations were found to be largestright above the ground and the vertical profiles suggest a weak mixingleading to terpene accumulation in the lower canopy. Exceptionally highvalues were recorded during a heat wave in July 2010 with very high middaytemperatures above 30 °C for several weeks. During summer months,monoterpene exceeded isoprene concentrations 6-fold and during winter12-fold. During summer months, dominance of α-pinene in the lower andof limonene in the upper part of the canopy was observed, both accounting forup to 70% of the total monoterpene concentration. During wintertime,Δ3-carene was the dominant species, accounting for 60% of totalmonoterpene concentration in January. Possible biogenic monoterpene sourcesbeside the foliage are the leaf litter, the soil and also resins exuding fromstems. In comparison, the hemiboreal mixed forest canopy showed similarisoprene but higher monoterpene concentrations than the boreal forest andlower isoprene but substantially higher monoterpene concentrations than thetemperate mixed forest canopies. These results have major implications forsimulating air chemistry and secondary organic aerosol formation within andabove hemiboreal forest canopies. Possible effects of in-cartridge oxidationreactions are discussed as our measurement technique did not include oxidantscavenging. A comparison between measurements with and without scavengingoxidants is presented

Seasonal variation in vertical volatile compounds air concentrations within a remote hemiboreal mixed forest