High emission rates and strong temperature response make boreal wetlands a large source of terpenes

• Main Authors: Vettikkat, Lejish, Miettinen, Pasi, Buchholz, Angela, Rantala, Pekka, Yu, Hao, Schallhart, Simon, Seco, Roger, Männistö, Elisa, Tuittila, Eeva-Stiina, Guenther, Alex B., Schobesberger, Siegfried
• Format: Text
• Language: English
• Published: 2022
• Subjects: Tundra
• Online Access: https://doi.org/10.5194/acp-2022-588; https://acp.copernicus.org/preprints/acp-2022-588/

Terpenes, a class of hydrocarbons including isoprene (C 5 H 8 ), monoterpenes (MTs; C 10 H 16 ), sesquiterpenes (SQTs; C 15 H 24 ), and diterpenes (DTs; C 20 H 32 ), are highly reactive to atmospheric oxidants and can form highly oxidized organic molecules (HOMs), leading to new particle formation (NPF), and secondary pollutants like tropospheric ozone and secondary organic aerosols (SOA). Wetlands are primarily found in the boreal and tundra regions of the Northern hemisphere and are well-known for their high methane emissions. However, their VOC emissions were investigated by relatively few studies, showing them to be high isoprene emitters. Terpene emissions have an exponential temperature dependence, while boreal wetlands are experiencing above two times the average global warming, and recent enclosure studies show a substantial increase in terpene emissions. In this study, we present ecosystem-scale eddy covariance (EC) fluxes of terpenes (up to DTs) from Siikaneva, a boreal fen in southern Finland, from the start to the peak of the growing season of 2021 (19 May 2021 to 28 June 2021). These are the first EC fluxes reported using the novel state-of-the-art Vocus- proton transfer reaction mass spectrometer (Vocus-PTR) and the first-ever fluxes reported for DTs from a wetland. Isoprene was the dominant terpene emitted by the wetland, followed by MTs, SQTs, and DTs. All terpenes exhibited distinct diurnal patterns with maxima around noon and a strong exponential dependence on temperature. The Q 10 values, the factor by which terpene emissions increases for every 10 °C rise in temperature, were up to 5 times higher than those used in most BVOC models. During the campaign, the air temperature peaked above 31 °C on 21–22 June 2021, which is abnormally high for boreal environments, and the maximum flux for all terpenes coincided with this period. We observed that terpene emissions were elevated after this abnormally “high-temperature stress period,” indicating that past temperatures alter emissions significantly. ...