A BIOGENIC HYDROCARBON EMISSION INVENTORY FOR THE USA USING A SIMPLE FOREST CANOPY MODEL

A biogenic hydrocarbon emission inventory system, developed for acid d eposition and regional oxidant modeling, is described, and results for a U.S. emission inventory are presented. For deciduous and coniferous forests, scaling relationships are used to account for canopy effects upon solar radiation, temperature, humidity and wind speed as a funct ion of height through the canopy. Leaf temperature is calculated itera tively from a leaf energy balance as a function of height through the canopy. The predicted light and temperature levels are used with mean empirical emission rate factors and laboratory emission algorithms to predict hydrocarbon emission rates. For application to a U.S. inventor y, diurnal emission fluxes of isoprene, alpha-pinene, other monoterpen es and other hydrocarbons are predicted for eight land cover classes b y state climatic division by month. The total U.S. emissions range fro m 22 to 50 Tg yr-1 depending upon the formulation of different emissio n rate factors. In the case where the forest canopy model is not used, the isoprene emissions increase by 50% and terpene emissions increase by 6%. In case study analyses, the predicted leaf temperatures were w ithin 1-2-degrees-C of observed for a deciduous forest, and predicted emissions were within a factor of two of observations. Further evaluat ion of the inventory using field measurements is required to determine the overall accuracy of the emission estimates.