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<p>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).</p> <p>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&thinsp;% of the isoprene emissions (mean isoprene emission over the growing season, 44&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻²</span>&thinsp;h<span class="inline-formula">⁻¹</span>), but sesquiterpene (SQT) emissions were higher than MT emissions all the time. The main MTs emitted were <span class="inline-formula"><i>α</i></span>-pinene, 1,8-cineol, myrcene, limonene and 3<span class="inline-formula">Δ</span>-carene. Of SQTs cadinene, <span class="inline-formula"><i>β</i></span>-cadinene and <span class="inline-formula"><i>α</i></span>-farnesene had the major contribution. During early growing season the SQT<span class="inline-formula">∕</span>MT emission rate ratio was <span class="inline-formula">∼10</span>, but it became smaller as summer proceeded, being only <span class="inline-formula">∼3</span> in July. Isoprene, MT and SQT emissions were exponentially dependent on temperature (correlation coefficients (<span class="inline-formula"><i>R</i>²</span>) 0.75, 0.66 and 0.52, respectively). Isoprene emission rates were also found to be exponentially correlated with the gross primary production of <span class="inline-formula">CO₂</span> (<span class="inline-formula"><i>R</i>²=0.85</span> in July).</p> <p>Even with the higher emissions from the wetland, ambient air concentrations of isoprene were on average &gt;&thinsp;100, &gt;&thinsp;10 and &gt;&thinsp;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 (<span class="inline-formula"><i>R</i>²=0.96</span>) with daily mean ozone concentrations indicating that vegetation emissions can be a significant chemical sink of ozone in this sub-Arctic area.</p>