Inventorying emissions from nature in Europe

As part of the work of the Economic Commission for Europe of the United Nat ions Task Force on Emission Inventories, a new set of guidelines has been d eveloped for assessing the emissions of sulphur, nitrogen oxides, NH,, CH,, and nonmethane volatile organic compounds (NMVOC) from biogenic and other natural sources in Europe. This paper gives the background to these guideli nes, describes the sources, and gives our recommended methodologies for est imating emissions. We have assembled land use and other statistics from Eur opean or national compilations and present emission estimates for the vario us natural/biogenic source categories based on these. Total emissions from nature derived here amount to similar to 1.1 Tg S yr(-1), 6-8 Tg CH4 yr(-1) , 70 Gg NH3 (as N) yr(-1), and 13 Tg NMVOC yr(-1). Estimates of biogenic NO x emissions cover a wide range, from 140 to 1500 Gg NOx (as N) yr(-1). In t erms of relative contribution to total European emissions for different pol lutants, then NMVOC from forests and vegetation are clearly the most import ant emissions source. Biogenic NOx emissions (although heavily influenced b y nitrogen inputs from anthropogenic activities) are very important if the higher estimates are reliable. CH, from wetlands and sulphur from volcanoes are also significant emissions in the European budgets. On a global scale, European biogenic emissions are not significant, a consequence of the clim ate and size (7% of global land area) of Europe and of the destruction of n atural ecosystems since prehistoric times. However, for assessing local bud gets and for photochemical oxidant modeling, natural/biogenic emissions can play an important role. The most important contributor in this regard is u ndoubtedly forest VOC emissions, although this paper also indicates that NM VOC emissions from nonforested areas also need to be further evaluated. Thi s paper was originally conceived as a contribution to the collection of pap ers arising as a result of the Workshop on Biogenic Hydrocarbons in the Atm ospheric Boundary Layer, August 24-27, 1997. (Several papers arising from t his workshop have been published in Journal of Geophysical Research, 103(D1 9) 1998.).