Abstract
Abstract. Atmospheric concentrations of methanol, acetaldehyde, acetone, isoprene and monoterpenes were measured using PTR-MS (proton transfer reaction mass spectrometry) in a boreal forest site in Hyytiälä, Finland (61°51' N, 24°17' E). The concentration measurements were made in the upper canopy of a Scots pine forest during 6 June, 2006–31 August, 2007. Meteorological variables such as temperature and photosynthetically active radiation were measured simultaneously. We also detected biologically sensitive turnover points such as the onsets of photosynthetic activity, onset of growing season, bud burst and stem growth during the annual cycle and compared them to changes in BVOC (biogenic volatile organic compound) concentrations. A typical seasonal pattern of winter minimum and summer maximum was found for all studied compounds except acetaldehyde. Spring time methanol and acetone concentrations increased together with photosynthetic capacity. The day-time daily median BVOC concentrations correlated best with air temperature. The intercorrelations between compounds and the analysis of meteorological conditions indicated that the measured concentrations presented well the local source. During an exceptional summer drought period the concentrations were neither connected with photosynthesis nor transpiration, but they were regulated by some other, yet unknown factors.
Highlights
Forests are a significant source of volatile organic compound (VOC) emissions
Once emitted into the atmosphere, the BVOCs may participate in the secondary organic aerosol (SOA) growth which is part of the atmospheric particle formation processes critical to the climate system (Kourtchev et al, 2008; Kulmala et al, 2004, 2007; Tunved et al, 2006)
The forest surrounding the SMEAR II site is rather homogenous, the local BVOC concentration could be affected by emissions transported from nearby sources, especially when compounds with long atmospheric lifetime are concerned (Rinne et al, 2007)
Summary
The emissions from boreal areas are less than those from temperate or tropical regions, but their contribution to regional BVOC (biogenic volatile organic compound) budget is significant (Guenther et al, 1995). Studies of BVOC emissions from the boreal forest zone consider mostly monoterpenes and isoprene, but boreal forests emit methanol, acetone and acetaldehyde (Janson et al, 1999; Janson and Serves, 2001; Rinne et al, 2007). Karst.) and some deciduous tree species like silver birch (Betula pubescens Ehrh.) are mainly monoterpene emitters, whereas trembling aspen (Populus tremula L.) and willow (Salix) species emit mostly isoprene (Janson and Serves, 2001; Hakola et al, 2000). Once emitted into the atmosphere, the BVOCs may participate in the secondary organic aerosol (SOA) growth which is part of the atmospheric particle formation processes critical to the climate system (Kourtchev et al, 2008; Kulmala et al, 2004, 2007; Tunved et al, 2006)
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