Articles | Volume 14, issue 17
Atmos. Chem. Phys., 14, 9087–9097, 2014
Atmos. Chem. Phys., 14, 9087–9097, 2014

Research article 05 Sep 2014

Research article | 05 Sep 2014

Uptake and emission of VOCs near ground level below a mixed forest at Borden, Ontario

M. Gordon1, A. Vlasenko*,1, R. M. Staebler1, C. Stroud1, P. A. Makar1, J. Liggio1, S.-M. Li1, and S. Brown2 M. Gordon et al.
  • 1Atmospheric Science and Technology Directorate, Science and Technology Branch, Environment Canada, Toronto, Canada
  • 2Agriculture and Forest Meteorology, Guelph University, Guelph, Canada
  • *now at: Airzone One Ltd., Mississauga, ON, Canada

Abstract. Understanding of the atmosphere/forest canopy exchange of volatile organic compounds (VOCs) requires insight into the deposition, emission, and chemical reactions of VOCs below the canopy. Between 18 July and 9 August 2009, VOCs were measured with proton-transfer-reaction mass spectrometry (PTR-MS) at six heights between 1 and 6 m beneath a 23 m high mixed-forest canopy. Measured VOCs included methanol, isoprene, acetone, methacrolein and methyl vinyl ketone (MACR + MVK), monoterpenes, and sesquiterpenes. There are pronounced differences in the behaviour of isoprene and its by-products and that of the terpenes. Non-terpene mixing ratios increase with height, suggesting predominantly downward fluxes. In contrast, the terpene mixing ratios decrease with height, suggesting upward fluxes. A 1-D canopy model was used to compare results to measurements with and without surface deposition of isoprene and MACR + MVK and emissions of monoterpenes and sesquiterpenes. Results suggest deposition velocities of 2.7 mm s−1 for isoprene and 1.2 mm s−1 for MACR + MVK and daytime surface emission rates of 63 μg m−2 h−1 for monoterpenes. The modelled isoprene surface deposition is approximately 2% of the canopy-top isoprene emissions and the modelled emissions of monoterpenes comprise approximately 15 to 27% of the canopy-top monoterpene emissions to the atmosphere. These results suggest that surface monoterpene emissions are significant for forest canopy/atmosphere exchange for this mixed-forest location and surface uptake is relatively small for all the species measured in this study.

Final-revised paper