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

by N. Yassaa, W. Song, J. Lelieveld, A. Vanhatalo, J. B??ck, J. Williams
Atmospheric Chemistry and Physics ()
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Branch enclosure based emission rates of monoterpenes and sesquiterpenes\nfrom four Scots pines (Pinus sylvestris) and one Norway spruce (Picea\nabies), as well as the ambient mixing ratios of monoterpenes were\ndetermined during the HUMPPA-COPEC 2010 summer campaign. Differences in\nchemical composition and in emission strength were observed between the\ndifferent trees, which confirmed that they represented different\nchemotypes. The chemotypes of Scots pine can be classified according to\nspecies with high, no and intermediate content of Delta-3-carene. The\n``non-Delta-3-carene{''} chemotype was found to be the strongest emitter\nof monoterpenes. From this chemotype, beta-myrcene, a very reactive\nmonoterpene, was the dominant species accounting for more than 32% of\nthe total emission rates of isoprenoids followed by beta-phellandrene\n(similar to 27 %). Myrcene fluxes ranged from 0.8 to 24 mu g g(-1) (dw)\nh(-1). Delta-Farnesene was the dominant sesquiterpene species, with\naverage emission rates of 318 ng g-1 (dw) h-1. In the high\nDelta-3-carene chemotype, more than 48% of the total monoterpene\nemission was Delta-3-carene. The average Delta-3-carene emission rate\n(from chemotype 3), circa 609 ng g-1 (dw) h-1 reported here is\nconsistent with the previously reported summer season value. Daily\nmaximum temperatures varied between 20 and 35 degrees C during the\nmeasurements. The monoterpene emissions from spruce were dominated by\nlimonene (35 %), beta-phellandrene (15 %), alpha-pinene (14 %) and\neucalyptol (9 %). Total spruce monoterpene emissions ranged from 0.55\nup to 12.2 mu g g-1 (dw) h-1. Overall the total terpene flux\n(monoterpenes + sesquiterpenes) from all studied tree species varied\nfrom 230 ng g-1 (dw) h-1 up to 66 mu g g-1 (dw) h-1. Total ambient\nmonoterpenes (including alpha-pinene, Delta-3-carene, Delta-pinene and\nDelta-myrcene) measured during the campaign varied in mixing ratio from\na few pptv to over one ppbv. The most abundant biogenic VOC measured\nabove the canopy were alpha-pinene and Delta-3-carene, and these two\ncompounds together contributed more than 50% of the total monoterpenes.\nThe ambient data reflect the emission rate, atmospheric reactivity and\ntree type abundance. The diel cycles of isoprenoid mixing ratios showed\nhigh levels during the night-time which is consistent with continued low\nnocturnal emission and a low and stable boundary layer. The chirality of\nalpha-pinene was dominated by (+)-enantiomers both in the direct\nemission and in the atmosphere. The two highest emitters showed no\nenantiomeric preference for alpha-pinene emissions, whereas the two\nlowest emitting pines emitted more (+)-enantiomer. The spruce emissions\nwere dominated by (-)-enantiomer. The exceptionally hot temperatures in\nthe summer of 2010 led to relatively strong emissions of monoterpenes,\ngreater diversity in chemical composition and high ambient mixing\nratios.

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