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

The present assessment of annual foliar emissions of non-methane volatile organic compounds (VOC) was carried out from a selection of 32 different varieties of trees representing 98% of the French forest. Experimental data were collected over a grid based on the 93 metropolitan departments (national districts). Specific emission potentials and foliar densities were individually assigned to each of the 32 species. Temperatures and light intensities were individually collected for all French departments. As far as possible, the specific emission factors taken into account in the algorithms used for calculating emission were characteristic of species growing in France or nearby. Average monthly and annual emissions of isoprene, monoterpenes and other volatile organic compounds (OVOC) were individually obtained for all departments and for France over the five-year period of the present investigation (1994–1998). The results indicate a periodical annual evolution of average emissions characterized by a rapid growth from March up to a maximum reached in July–August and followed by a net decrease in September–October. The emissions recorded during the months of July and August represent more 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, respectively, 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 anthropogenic sources. As a whole, the results are affected by a rather large uncertainty, due to the importance of calculated corrective factors, ranged between 4 and 7.