Emissions and ambient air concentrations of isoprene, monoterpenes and sesquiterpenes at a Northern wetland
- Finnish Meteorological Institute, Atmospheric composition research, Helsinki, Finland (heidi.hellen@fmi.fi)
Wetlands cover an area of about 2% of the total land surface area of the world and are most common in the boreal and tundra zones. Northern wetlands are important sinks for carbon dioxide and sources of methane, but knowledge on their VOC emissions is very limited. Currently, we know that northern wetlands are high isoprene emitters (e.g. Holst et al., 2010), but very little is known on the emissions of other VOCs.
We have studied VOC emissions and their ambient concentrations at a sub-Arctic wetland (Lompolojänkkä) in Northern Finland, using an in situ TD-GC-MS. For the emission measurements, a dynamic flow-through FEP chamber was used.
Earlier studies have shown that isoprene is emitted from 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 at all times. Both MT and SQT emissions were dependent on temperature.
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 (Hellén et al., 2018). 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.
References
Hellén, H.et al. 2018, Atmos. Chem. Phys., 18, 13839-13863, https://doi.org/10.5194/acp-18-13839-2018.
Holst, T., et al. 2010, Atmos. Chem. Phys., 10, 1617-1634, https://doi.org/10.5194/acp-10-1617-2010.
How to cite: Hellén, H., Schallhart, S., Praplan, A. P., Tykkä, T., Aurela, M., Lohila, A., and Hakola, H.: Emissions and ambient air concentrations of isoprene, monoterpenes and sesquiterpenes at a Northern wetland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4938, https://doi.org/10.5194/egusphere-egu2020-4938, 2020
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Dear Authors,
This is a highly interesting issue, especially concerning the release sesquiterpenes from soils. Soils as a sesquiterpene source have been demonstrated recently also for Amazonian forest soils by Bourtsoukidis et al. 2018; https://doi.org/10.1038/s41467-018-04658-y . You will know this article. May be this source is generally underestimated.
I have two questions.
1. In your introduction you state that wetlands represent about 2% of the total land surface area of the world. May be this number is too small? I would expect a number of around 8%. Did you relate the wetland surface to the total surface area of the world instead to the land surface area only?
2. Sesquiterpenes and some monoterpenes are highly reactive. In some cases the detection of such compounds in the ambient air is critical because of fast oxidation processes to other products. Did you take care for this problem within your chamber measurements by using oxidant free air for flushing the chambers?
Thanks,
Jürgen Kesselmeier, Max Planck Institute for Chemistry, Mainz, Germany
Dear Professor Kesselmeir,
Thank you for the very good comments!
Best regards,
Heidi Hellén
Thanks a lot Heidi!
That sounds convincing.
Jürgen