AN EMISSIONS INVENTORY FOR REGIONAL ATMOSPHERIC MODELING OF MERCURY

Estimates of mercury emissions from individual sources and source cate gories are needed to understand relationships between the emissions an d resulting deposition and to evaluate possible approaches to reducing those emissions. We have developed geographically-resolved estimates of annual average mercury emission rates from current anthropogenic so urces in the 48 contiguous United States. These estimates were made by applying emission factors to individual facility operating data and t o county-wide source activity levels. We apportioned the emissions to an Eulerian modeling grid system using point source coordinates and th e fractions of county areas in each grid cell, Point sources account f or about 89% of the 48-state total mercury emissions of 146.4 Mg/yr. M ost of the emissions in the inventory are from combustion of mercury-c ontaining fossil fuels and municipal waste, located primarily in the m id-Atlantic and Great Lakes states as well as in the Southeast, The ma jor uncertainties in the emission estimates are caused by uncertaintie s in the emission factors used to develop the estimates. This uncertai nty is likely a result of variability ir:the mercury content of the co mbusted materials and in the removal of mercury by air pollution contr ol devices. The greatest research need to reduce uncertainties in merc ury emission estimates is additional measurements to improve emission factors.