Terpenoid measurements at a Northern wetland revealed a strong source of sesquiterpenes

• Main Authors: Hellén, Heidi, Schallhart, Simon, Praplan, Arnaud P., Tykkä, Toni, Aurela, Mika, Lohila, Annalea, Hakola, Hannele
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Sodankylä
• Online Access: https://doi.org/10.5194/acp-2019-1154; https://www.atmos-chem-phys-discuss.net/acp-2019-1154/

We have studied biogenic VOC 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 turned out to be the most abundant compound in the current study also. Monoterpene (MT) emissions were generally less than 10 % of the isoprene emissions, but sesquiterpenes (SQT) emissions were surprisingly high exceeding MT emissions all the time. During early growing season SQT emission rates were about ten times higher than MT emission rates but this difference became smaller as summer proceeded. Isoprene, MT and SQT emissions were dependent on temperature. Isoprene emission rates were also found to be well-correlated with the gross primary production of CO 2 . Even with the higher emissions from the wetland, ambient air concentrations of isoprene were clearly lower than MT concentrations. 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. In May concentrations of SQTs and MTs at Lompolojänkkä were higher than in earlier boreal forest measurements in southern Finland. At that time the snow cover on the ground was melting and soil thawing and VOCs produced under the snow cover, e.g. by microbes and decaying litter, can be released to the air. Daily mean MT concentrations were very highly negatively correlated with daily mean ozone concentrations indicating that vegetation emissions can be a significant chemical sink of ozone at this sub-Arctic area.