Ratios between the normalized emission rates E_k (t) varying over the time.

<p>Different panels indicate ratios of <i>m/z</i> = 83.085/<i>m/z</i> = 81.070 (a) and <i>m/z</i> 143.107/<i>m/z</i> 81.070 (b) emitted after cutting leaves of <i>Dactlylis glomerata</i> (red lines) and of <i>Populus alba</i> (dark red lines) or after exposing to light to dark transition leaves of <i>Dactlylis glomerata</i> (blue lines) and of <i>Populus alba</i> (dark blue lines).</p

Relationship between constitutive carbon emitted as isoprenoids (isoprene in <i>P. alba</i>; monoterpenes in <i>Q. ilex</i>) and the total amount of carbon emitted as acetaldehyde after fast transition from light to dark conditions (linear regression R² = 0.55).

<p>The emission measured in 3 different leaves of <i>P. alba</i> (black circles) and 4 different leaves of <i>Q. ilex</i> (white circles) are shown. Each leaf was selected from different individuals in both plant species.</p

Total amount of BVOCs emitted (µmol m²) and relative percentage (%) of the major ions representing the BVOCs blend emitted after transition from light to dark conditions in <i>Dactlylis glomerata</i>, <i>Quercus</i> ilex, <i>Populus alba</i> intact leaves and in <i>Populus alba</i> leaves after the petiole has been excised.

<p>Means ± SE are shown (<i>n</i> = 4). Differences between means within the same column were statistically assessed with a Tukey's post hoc test (<i>P</i><0.05).</p

Release of GLVs after wounding <i>Dactlylis glomerata</i> plants kept in dark conditions (24 hours/day) for 7 days long (DA) compared to <i>Dactlylis glomerata</i> plants kept under standard circadian rhythm (12 hours light+12 hours dark) (STD).

<p>Different colors indicate different ions: <i>m/z</i> = 81.070 [(<i>Z</i>)-3-hexenal+(<i>E</i>)-3-hexenal]; <i>m/z</i> = 83.085 [(<i>Z</i>)-3-hexenol+(<i>E</i>)-3-hexenol+(<i>E</i>)-2-hexenol+hexanal]. Data shown are from a single leaf but are representative of experiments replicated four times on different leaves.</p

Effect of cutting on BVOCs emission (a), (b) and gas exchange (c) of a <i>Populus alba</i> leaf.

<p>At the time indicated by the arrow, the leaf petiole was excised and the light was switched off during the time indicated by the striped background. Different colors indicate different ions: (a) <i>m/z</i> = 81.070 [(<i>Z</i>)-3-hexenal+(<i>E</i>)-3-hexenal]; <i>m/z</i> = 83.085 [(<i>Z</i>)-3-hexenol+(<i>E</i>)-3-hexenol+(<i>E</i>)-2-hexenol+hexanal]; <i>m/z</i> = 43.018 [hexyl acetates]; <i>m/z</i> = 143.107 [hexenyl acetates]. (b) <i>m/z</i> = 33.034 [methanol]; <i>m/z</i> = 45.054 [acetaldehyde]; <i>m/z</i> = 71.086 [pentenal fragment]; <i>m/z</i> = 69.069 [isoprene]. (c) Photosynthetic carbon assimilation (black circles) and stomatal conductance (open circles). One typical sequence out of four independent experiments is shown.</p

Total amount of green leaves volatiles (GLVs) (µmol mm⁻¹) and percentage (%) of the major ions representing the GLVs blend emitted after wounding <i>Dactlylis glomerata</i> and <i>Populus alba</i> leaves grown in normal circadian light cycle compared to those exposed to continuous dark conditions for 7 days.

<p>Means ± SE are shown (<i>n</i> = 4). Differences between means within the same column were statistically assessed with a Tukey's post hoc test (<i>P</i><0.05).</p

Time course of BVOCs emitted from wounded <i>Dactlylis glomerata</i> leaves PTR-TOF detected during the same measurement.

<p>Different colors and symbols indicate different ions: (a) <i>m/z</i> = 81.070+<i>m/z</i> = 99.080 [(<i>Z</i>)-3-hexenal+(<i>E</i>)-3-hexenal]; <i>m/z</i> = 57.033 (<i>E</i>)-2-hexenal; (b) <i>m/z</i> = 83.085+<i>m/z</i> = 101.096 [(<i>Z</i>)-3-hexenol+(<i>E</i>)-3-hexenol+(<i>E</i>)-2-hexenol+hexanal]; <i>m/z</i> = 85.101 [hexanol]; <i>m/z</i> = 143.107 [(<i>Z</i>)-3-hexenyl acetate+(<i>E</i>)-2-hexenyl acetate]; (c) <i>m/z</i> = 33.034 [methanol]; <i>m/z</i> = 45.034 [acetaldehyde]; <i>m/z</i> = 85.064 [pentenone]; <i>m/z</i> = 69.070 [isoprene] and <i>m/z</i> = 71.086 [pentenal fragment]. Data shown are from a single leaf but are representative of experiments replicated four times on different leaves.</p

Molecular Composition of Boreal Forest Aerosol from Hyytiälä, Finland, Using Ultrahigh Resolution Mass Spectrometry

Organic compounds are important constituents of fine particulate matter (PM) in the troposphere. In this study, we applied direct infusion nanoelectrospray (nanoESI) ultrahigh resolution mass spectrometry (UHR-MS) and liquid chromatography LC/ESI-UHR-MS for the analysis of the organic fraction of PM₁ aerosol samples collected over a two week period at a boreal forest site (Hyytiälä), southern Finland. Elemental formulas (460–730 in total) were identified with nanoESI-UHR-MS in the negative ionization mode and attributed to organic compounds with a molecular weight below 400. Kendrick Mass Defect and Van Krevelen approaches were used to identify compound classes and mass distributions of the detected species. The molecular composition of the aerosols strongly varied between samples with different air mass histories. An increased number of nitrogen, sulfur, and highly oxygenated organic compounds was observed during the days associated with continental air masses. However, the samples with Atlantic air mass history were marked by a presence of homologous series of unsaturated and saturated C₁₂–C₂₀ fatty acids suggesting their marine origin. To our knowledge, we show for the first time that the highly detailed chemical composition obtained from UHR-MS analyses can be clearly linked to meteorological parameters and trace gases concentrations that are relevant to atmospheric oxidation processes. The additional LC/ESI-UHR-MS analysis revealed 29 species, which were mainly attributed to oxidation products of biogenic volatile compounds BVOCs (i.e., α,β-pinene, Δ₃-carene, limonene, and isoprene) supporting the results from the direct infusion analysis

Total amount (mass) of ions <i>m/z</i> = 81.070 [(<i>Z</i>)-3-hexenal+(<i>E</i>)-3-hexenal] (black circles) and <i>m/z</i> = 83.085 [(<i>Z</i>)-3-hexenol+(<i>E</i>)-3-hexenol+(<i>E</i>)-2-hexenol+hexanal] (open circles) as a function of cut lengths [mm] produced when wounding <i>Dactlylis glomerata</i> leaves (R² = 0.91 solid line; R² = 0.88 dotted line).

<p>Circles represent results from 7 experiments carried out on single leaves.</p

Time course of BVOC emission and gas exchange of intact <i>Dactlylis glomerata</i> (a, d, g), <i>Populus alba</i> (b, e, h) and <i>Quercus ilex</i> (c, f, i) leaves following rapid light-dark transitions.

<p>The light was switched off at the time indicated by the arrows. Different colors indicate different ions: (a, b, c) <i>m/z</i> = 81.070 [(<i>Z</i>)-3-hexenal+(<i>E</i>)-3-hexenal]; <i>m/z</i> = 83.085 [(<i>Z</i>)-3-hexenol+(<i>E</i>)-3-hexenol+(<i>E</i>)-2-hexenol+hexanal]; <i>m/z</i> = 43.018 [hexyl acetates]; m/z = 143.107 [(<i>Z</i>)-3-hexenyl acetate+(<i>E</i>)-2-hexenyl acetate]. (d, e, f) <i>m/z</i> = 33.034 [methanol]; <i>m/z</i> = 45.054 [acetaldehyde]; <i>m/z</i> = 69.070 [isoprene] (only in <i>P. alba -</i> panel e); <i>m/z</i> = 71.086 [pentenal fragment]; <i>m/z</i> = 137.133 [monoterpenes] (only in <i>Q. ilex -</i> panel f). (g, h, i) Photosynthetic carbon assimilation (black circles) and stomatal conductance (open circles). One typical sequence out of four independent experiments is shown.</p