Abstract
Abstract. The concentrations of terpenoids (isoprene; monoterpenes, MTs; and sesquiterpenes, SQTs) and oxygenated volatile organic compounds (OVOCs; i.e. aldehydes, alcohols, acetates and volatile organic acids, VOAs) were investigated during 2 years at a boreal forest site in Hyytiälä, Finland, using in situ gas chromatograph mass spectrometers (GC-MSs). Seasonal and diurnal variations of terpenoid and OVOC concentrations as well as their relationship with meteorological factors were studied. Of the VOCs examined, C2–C7 unbranched VOAs showed the highest concentrations, mainly due to their low reactivity. Of the terpenoids, MTs showed the highest concentrations at the site, but seven different highly reactive SQTs were also detected. The monthly and daily mean concentrations of most terpenoids, aldehydes and VOAs were highly dependent on the temperature. The highest exponential correlation with temperature was found for a SQT (β-caryophyllene) in summer. The diurnal variations in the concentrations could be explained by sources, sinks and vertical mixing. The diurnal variations in MT concentrations were strongly affected by vertical mixing. Based on the temperature correlations and mixing layer height (MLH), simple proxies were developed for estimating the MT and SQT concentrations. To estimate the importance of different compound groups and compounds in local atmospheric chemistry, reactivity with main oxidants (hydroxyl radical, OH; nitrate radical, NO3; and ozone, O3) and production rates of oxidation products (OxPRs) were calculated. The MTs dominated OH and NO3 radical chemistry, but the SQTs greatly impacted O3 chemistry, even though the concentrations of SQT were 30 times lower than the MT concentrations. SQTs were also the most important for the production of oxidation products. Since the SQTs show high secondary organic aerosol (SOA) yields, the results clearly indicate the importance of SQTs for local SOA production.
Highlights
The boreal forest is one of the largest terrestrial biomes in the world, forming an almost continuous belt around the Northern Hemisphere
Oxygenated VOCs (OVOCs) emitted from the vegetation include carbonyls, alcohols and volatile organic acids (VOAs), but their emissions are less studied and they are produced in the atmosphere from the reactions of VOCs
For aromatic hydrocarbons, which are mainly emitted from anthropogenic sources, the concentrations were higher in winter
Summary
The boreal forest is one of the largest terrestrial biomes in the world, forming an almost continuous belt around the Northern Hemisphere. Data on the concentrations of individual MTs measured by gas chromatograph mass spectrometers (GC-MSs) are scarce and often available only from short measurement campaigns (Kesselmeier et al, 2002; Hakola et al, 2003, 2009; Jones et al, 2011; Yassaa et al, 2012; Jardine et al, 2015; Yáñez-Serrano et al, 2018) Emissions of both MTs and SQTs have been studied in various vegetation zones (Guenther et al, 2012), but to our knowledge only three studies are available on the atmospheric concentrations of individual SQTs (Bouvier-Brown et al, 2009; Hakola et al, 2012; Yee et al, 2018). To estimate the importance of the individual VOCs or VOC groups for the local atmospheric chemistry and SOA production, reactivities and the production rates of oxidation products were calculated
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