Natural ecosystems such as forests are important emission sources of Biogenic Volatile Organic Compounds (BVOC). On a global scale, BVOC emissions (~ 1150 Tg C per year) were estimated to be an order of magnitude larger than their anthropogenic counterparts (Guenther et al. 1995). Due to their large emissions and their high reactivity with the main oxidants (OH, O3, NO3) in the atmosphere (Atkinson and Arey 2003), BVOCs are expected to contribute significantly to atmospheric chemistry, and to have as such an important impact on air quality.

During the last decade, numerous emission studies have been performed and species-specific BVOC standard emission inventories have been started (e.g. the Lancaster University database (UK) or the ACD/NCAR database). Photosynthetic active radiation (PAR) and leaf temperature have long been recognized as important factors controlling emissions from tree foliage, and currently used BVOC emission algorithms are mainly a function of these two parameters. Recent studies have shown that other parameters such as leaf age, leaf growth environment, nitrogen content of the plant, water availability, leaf photosynthesis, relative humidity and CO2 concentration in the air can also have a significant influence on the emissions. However, experimental data on how forest ecosystem functioning is contributing to these BVOC emissions, and how this contribution responds to varying environmental conditions during the year are still scarce. Therefore, more measurements of BVOC emission dynamics, together with plant physiological activity are clearly needed.

Recently, rapid and sensitive technologies (such as the Proton Transfer Reaction Mass Spectrometer (PTR-MS)) have become available. In combination with high frequency vertical air velocity measurements, these new techniques can even be used to perform direct above-canopy eddy covariance flux measurements and thus to estimate BVOC exchange at stand level.

The subject of the IMPECVOC project is the detailed analysis of the emissions of BVOCs occurring from deciduous (European beech) and coniferous (Douglas fir and Norway spruce) tree species growing in Belgian forest ecosystems. The driving variables behind BVOC emissions of the tree species need to be unravelled by means of well-conceived studies. In order to better understand the effects of environmental and ecophysiological parameters on the emissions, detailed studies at a low organisational level (e.g. leaf level) will be conducted and compared to BVOC emission dynamics at canopy and stand level. These studies will result in new parameterizations of BVOC emissions involving multiple parameters. In combination with a well-validated canopy model and with detailed data for land use, species composition and biomass density, they will result in more accurate BVOC emissions inventories, in particular for Belgium.

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