Sesquiterpenes dominate monoterpenes in northern wetland emissions
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Published:2020-06-12
Issue:11
Volume:20
Page:7021-7034
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Hellén HeidiORCID, Schallhart Simon, Praplan Arnaud P.ORCID, Tykkä Toni, Aurela MikaORCID, Lohila AnnaleaORCID, Hakola Hannele
Abstract
Abstract. We have studied biogenic volatile
organic compound (BVOC) emissions and their ambient
concentrations at a sub-Arctic wetland (Lompolojänkkä, Finland),
which is an open, nutrient-rich sedge fen and a part of the
Pallas-Sodankylä Global Atmosphere Watch (GAW) station. Measurements
were conducted during the growing season in 2018 using an in situ thermal-desorption–gas-chromatograph–mass-spectrometer (TD-GC-MS). Earlier studies have shown that isoprene is emitted from boreal wetlands, and
it also turned out to be the most abundant compound in the current study.
Monoterpene (MT) emissions were generally less than 10 % of the isoprene
emissions (mean isoprene emission over the growing season, 44 µg m−2 h−1), but sesquiterpene (SQT) emissions were higher than MT
emissions all the time. The main MTs emitted were α-pinene,
1,8-cineol, myrcene, limonene and 3Δ-carene. Of SQTs cadinene,
β-cadinene and α-farnesene had the major contribution. During early growing season the SQT∕MT emission rate ratio was ∼10, but
it became smaller as summer proceeded, being only ∼3 in July.
Isoprene, MT and SQT emissions were exponentially dependent on temperature
(correlation coefficients (R2) 0.75, 0.66 and 0.52, respectively).
Isoprene emission rates were also found to be exponentially correlated with
the gross primary production of CO2 (R2=0.85 in July). Even with the higher emissions from the wetland, ambient air concentrations
of isoprene were on average > 100, > 10 and
> 6 times lower than MT concentrations in May, June and July,
respectively. This indicates that wetland was not the only source affecting
atmospheric concentrations at the site, but surrounding coniferous forests,
which are high MT emitters, contribute as well. Daily mean MT concentrations
had high negative exponential correlation (R2=0.96) with daily mean
ozone concentrations indicating that vegetation emissions can be a
significant chemical sink of ozone in this sub-Arctic area.
Funder
Academy of Finland
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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