A Model to Calculate Natural VOC Emissions from Forests in Europe

A significant portion of the total emissions of volatile organic compounds (VOC) may come from natural sources and, in particular, from forests. It is important to quantify these emissions because their share influences the magnitude of reductions that will have to be undertaken in the anthropogenic emission sectors in order to reduce secondary air pollution problem such as photochemical smog and acid deposition. This paper describes a model to calculate geographically-resolved VOC emissions from forests in Europe for different seasons, months or average days. We review briefly the method on how to calculate biogenic emissions from trees and available emission factor functions, including a discussion of the dependence of emissions on latitude, altitude, time of the day and temperature. Subsequently, the geographically-resolved forest and temperature data bases for Europe, as used in this model to derive the emission estimates, are described. The forest data are verified against other published forest inventories for Europe or parts of Europe. The resulting total VOC emissions are compared with existing country- or region-specific estimates, and some sensitivity analyses are carried out in order to show where the emission model could be simplified or where it needs to be improved. Based on our total forest coverage of approximately 2.2 million km^2, we calculate an average total annual emission rate of VOC's from these forests of 7.5 Megatonnes, based on typical European temperatures averaged over 30 years. This is equivalent to an areal average of 3.4 tonnes per year per km^2 forest or 0.9 tonnes per year per km^2 land area in the modeling domain. Until now, this forest emission model represents the only available basis for geographically-resolved emission calculations of VOC's from forests for all Europe for varying time periods