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https://doi.org/10.5194/bg-2020-37
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-37
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Mar 2020

Submitted as: research article | 03 Mar 2020

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This preprint is currently under review for the journal BG.

OH reactivity from different tree species: Investigating the missing reactivity in a boreal forest

Arnaud P. Praplan1, Toni Tykkä1, Simon Schallhart1, Virpi Tarvainen1, Jaana Bäck2, and Heidi Hellén1 Arnaud P. Praplan et al.
  • 1Atmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
  • 2Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, P.O. Box 27, 00014 University of Helsinki, Finland

Abstract. In forested area, a large fraction of total hydroxyl radical (OH) reactivity remain unaccounted for. Very few studies have been looking at total OH reactivity from biogenic emissions and its variations. In the present study, we investigate the total OH reactivity from three common boreal tree species (Scots pine, Norway spruce, and Downy birch), by comparing it with the calculated reactivity from the chemically identified emissions. Total OH reactivity was measured using the Comparative Reactivity Method (CRM), and the chemical composition of the emissions was quantified with two gas chromatographs coupled to mass spectrometers (GC-MSs). Dynamic branch enclosures were used and emissions from one branch of a tree at the time were measured by rotating between them periodically. Results show that birch had the highest values of total OH reactivity of the emissions (TOHRE), while pine had the lowest. The main drivers for the known reactivity of pine and spruce were monoterpenes and sesquiterpenes. For birch, emissions were dominated by sesquiterpenes, even though monoterpenes and GLVs could be found too. However, calculated reactivity values remained low leading to the highest missing fraction of reactivity (>96 %), while pine and spruce had similar missing reactivity fractions between 56 % and 82 % (higher in the spring and decreasing as the summer proceeded). The high average values were driven by low reactivity periods and the fraction of missing reactivity got smaller for pine and spruce when the TOHRE values increased. Important exceptions were identified for periods when the emission profiles changed from terpenes to Green Leaf Volatiles (GLVs), a family of compounds containing a 6 carbon atoms backbone with various functionalities (e.g. alcohols, aldehydes, esters) that indicate that the plant is suffering from stress. Then, very high TOHRE values were measured and the missing fraction remained high. This study found a different trend in the missing OHRE fraction of Norway spruce from spring to autumn compared to one previous study (Nölscher et al., 2013), which indicates that additional studies are required to fully understand the complexity of biogenic reactive emissions. Future studies of boreal trees in situ should be conducted to confirm the findings presented.

Arnaud P. Praplan et al.

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Arnaud P. Praplan et al.

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Latest update: 04 Apr 2020
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Short summary
In this paper, we study emissions of Volatile Organic Compounds (VOCs) from three boreal tree species. Individual compounds are quantified with on-line separation analytical techniques, while the total reactivity of the emissions is measured using a custom-built instrument. On some occasion, in particular when the trees suffer from stress, the total reactivity measured is higher than the sum of the reactivity of individual compounds. This indicates that the threes emit VOCs that remain unknown.
In this paper, we study emissions of Volatile Organic Compounds (VOCs) from three boreal tree...
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