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.
Highlights
Many plants communicate by releasing massive amounts of biogenic volatile organic compounds (BVOCs) into the air
The measurement set-up consisted of a 60×60×25 cm fluorinated ethylene propylene (FEP) chamber, which was flushed with 4 L min−1 of volatile organic compound (VOC) free air generated by a commercial catalytic converter (HPZA7000, Parker Hannifin Corporation)
MT emissions were generally less than 10 % of the isoprene emissions, but SQT emissions were surprisingly high and exceeded MT emissions all the time (Table 1 and Fig. 2)
Summary
Many plants communicate by releasing massive amounts of biogenic volatile organic compounds (BVOCs) into the air They can either attract pollinators, repel herbivores or respond to other stress. Knowledge of the biogenic emissions in the subArctic/Arctic area is very limited, at least partly because emissions are assumed to be low there due to low temperatures, short summers and low vegetation biomass. Atmospheric reactions such as SOA and ozone formation/destruction are regional rather than global processes (Tunved et al, 2006). We have studied VOC emissions and their ambient concentrations at a Finnish sub-Arctic wetland (Lompolojänkkä), which is an open, nutrient-rich sedge fen (Lohila et al, 2015) and a part of the Pallas-Sodankylä Global Atmosphere Watch (GAW) station
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