17 Nov 2022
17 Nov 2022
Status: this preprint is open for discussion.

Vertical distribution of sources and sinks of VOCs within a boreal forest canopy

Ross Charles Petersen1, Thomas Holst1, Meelis Mölder1, Natascha Kljun2, and Janne Rinne1,3 Ross Charles Petersen et al.
  • 1Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden
  • 2Centre for Environmental and Climate Science, Lund University, Lund, Sweden
  • 3Natural Resources Institute Finland (Luke), Helsinki, Finland

Abstract. The ecosystem-atmosphere flux of biogenic volatile organic compounds (BVOCs) has important impacts on tropospheric oxidative capacity and the formation of secondary organic aerosols, influencing air quality and climate. Here we present within-canopy measurements of a set of dominant BVOCs in a managed spruce- and pine-dominated boreal forest located at the ICOS station Norunda in Sweden, collected using proton transfer reaction mass spectrometry (PTR-MS) during 2014–2016, and vertical emission profiles derived from these data. Ozone concentrations were simultaneously measured in conjunction with these PTR-MS measurements. The main BVOCs investigated with the PTR-MS were isoprene, monoterpenes, methanol, acetaldehyde, and acetone. The distribution of BVOC sources and sinks in the forest canopy was explored using Lagrangian dispersion matrix methods, in particular continuous near-field theory. The forest canopy was found to contribute ca. 86 % to the total monoterpene emission in summertime, whereas the below-canopy and canopy emission was comparable (ca. 42 % and 58 % respectively) during the autumn period. This result indicates that boreal forest litter and other below-canopy emitters are a principle source for total forest monoterpene emissions during autumn months. During night, our results for methanol, acetone, and acetaldehyde seasonally present strong sinks in the forest canopy, especially in the autumn, likely due to the nighttime formation of dew on vegetation surfaces.

Ross Charles Petersen et al.

Status: open (until 05 Jan 2023)

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Ross Charles Petersen et al.

Ross Charles Petersen et al.


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Short summary
We investigate variability in the vertical distribution of volatile organic compounds (VOCs) in boreal forest, determined through multi-year measurements at several heights at a boreal forest in Sweden. VOC source/sink seasonality in canopy was explored using these vertical profiles and with measurements from a collection of sonic anemometers on the station flux tower. Our results show seasonality in the source/sink distribution for several VOCs, such as monoterpenes and water-soluble compounds.