Estimating the emission of volatile organic compounds (VOC) from the French forest ecosystem

The present assessment of annual foliar emissions of non-methane volatile o rganic compounds (VOC) was carried out from a selection of 32 different var ieties of trees representing 98% of the French forest. Experimental data we re collected over a grid based on the 93 metropolitan departments (national districts). Specific emission potentials and foliar densities were individ ually assigned to each of the 32 species. Temperatures and light intensitie s were individually collected for all French departments. As far as possibl e, the specific emission factors taken into account in the algorithms used for calculating emission were characteristic of species growing in France o r nearby. Average monthly and annual emissions of isoprene, monoterpenes an d other volatile organic compounds (OVOC) were individually obtained for al l departments and for France over the five-year period of the present inves tigation (1994-1998). The results indicate a periodical annual evolution of average emissions characterized by a rapid growth from March up to a maxim um reached in July-August and followed by a net decrease in September-Octob er. The emissions recorded during the months of July and August represent m ore than 50% of the annual values. Over the whole country, isoprene appears as the most abundant species, with an emission of 457 kt yr(-1), followed by monoterpenes, 350 kt yr(-1) and OVOC, 129 kt yr(-1), such values, respec tively, representing 49, 37 and 14% of the total emission. The level of VOC emissions of biogenic origin in France is 50% lower than that of anthropog enic sources. As a whole, the results are affected by a rather large uncert ainty, due to the importance of calculated corrective factors, ranged betwe en 4 and 7. (C) 2001 Elsevier Science Ltd. All rights reserved.