Index Geophysics

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

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.

Gordon, M.

Vlasenko, A.

Staebler, R. M.

Stroud, C.

Makar, P. A.

Liggio, J.

Li, S.-M.

Brown, S.

2018-09-08

Text

application/pdf

10.5194/acp-14-9087-2014

https://acp.copernicus.org/articles/14/9087/2014/

eISSN: 1680-7324

eng