A GLOBAL-MODEL OF NATURAL VOLATILE ORGANIC-COMPOUND EMISSIONS

Numerical assessments of global air quality and potential changes in a tmospheric chemical constituents require estimates of the surface flux es of a variety of trace gas species. We have developed a global model to estimate emissions of volatile organic compounds from natural sour ces (NVOC). Methane is not considered here and has been reviewed in de tail elsewhere. The model has a highly resolved spatial grid (0.5 degr ees x 0.5 degrees latitude/longitude) and generates hourly average emi ssion estimates. Chemical species are grouped into four categories: is oprene, monoterpenes, other reactive VOC (ORVOC), and other VOC (OVOC) . NVOC emissions from oceans are estimated as a function of geophysica l variables from a general circulation model and ocean color satellite data. Emissions from plant foliage are estimated from ecosystem speci fic biomass and emission factors and algorithms describing light and t emperature dependence of NVOC emissions. Foliar density estimates are based on climatic variables and satellite data. Temporal variations in the model are driven by monthly estimates of biomass and temperature and hourly light estimates. The annual global VOC flux is estimated to be 1150 Tg C, composed of 44% isoprene, 11% monoterpenes, 22.5% other reactive VOC, and 22.5% other VOC. Large uncertainties exist for each of these estimates and particularly for compounds other than isoprene and monoterpenes. Tropical woodlands (rain forest, seasonal, drought- deciduous, and savanna) contribute about half of all global natural VO C emissions. Croplands, shrublands and other woodlands contribute 10-2 0% apiece. Isoprene emissions calculated for temperate regions are as much as a factor of 5 higher than previous estimates.