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Branch enclosure based emission rates of monoterpenes and sesquiterpenes fromfour Scots pines (Pinus sylvestris) and one Norway spruce(Picea abies), as well as the ambient mixing ratios of monoterpeneswere determined during the HUMPPA-COPEC 2010 summer campaign. Differences inchemical composition and in emission strength were observed between thedifferent trees, which confirmed that they represented different chemotypes.The chemotypes of Scots pine can be classified according to species withhigh, no and intermediate content of Δ-3-carene. The"non-Δ-3-carene" chemotype was found to be the strongest emitter ofmonoterpenes. From this chemotype, β-myrcene, a very reactivemonoterpene, was the dominant species accounting for more than 32 % of thetotal emission rates of isoprenoids followed by β-phellandrene(~27%). Myrcene fluxes ranged from 0.8 to24 μg g−1 (dw) h−1. α-Farnesene was thedominant sesquiterpene species, with average emission rates of318 ng g−1 (dw) h−1. In the high Δ-3-carene chemotype,more than 48% of the total monoterpene emission was Δ-3-carene. Theaverage Δ-3-carene emission rate (from chemotype 3), circa609 ng g−1 (dw) h−1 reported here is consistent with thepreviously reported summer season value. Daily maximum temperatures variedbetween 20 and 35 °C during the measurements. The monoterpeneemissions from spruce were dominated by limonene (35%),β-phellandrene (15%), α-pinene (14%) and eucalyptol(9%). Total spruce monoterpene emissions ranged from 0.55 up to12.2 μg g−1 (dw) h−1. Overall the total terpene flux(monoterpenes + sesquiterpenes) from all studied tree species varied from230 ng g−1 (dw) h−1 up to66 μg g−1 (dw) h−1. Total ambient monoterpenes(including α-pinene, Δ-3-carene, β-pinene andβ-myrcene) measured during the campaign varied in mixing ratio from afew pptv to over one ppbv. The most abundant biogenic VOC measured abovethe canopy were α-pinene and Δ-3-carene, and these twocompounds together contributed more than 50% of the total monoterpenes.The ambient data reflect the emission rate, atmospheric reactivity and treetype abundance. The diel cycles of isoprenoid mixing ratios showed highlevels during the night-time which is consistent with continued low nocturnalemission and a low and stable boundary layer. The chirality ofα-pinene was dominated by (+)-enantiomers both in the direct emissionand in the atmosphere. The two highest emitters showed no enantiomericpreference for α-pinene emissions, whereas the two lowest emittingpines emitted more (+)-enantiomer. The spruce emissions were dominated by(−)-enantiomer. The exceptionally hot temperatures in the summer of 2010led to relatively strong emissions of monoterpenes, greater diversity inchemical composition and high ambient mixing ratios

Diel cycles of isoprenoids in the emissions of Norway spruce, four Scots pine chemotypes, and in Boreal forest ambient air during HUMPPA-COPEC-2010