Assessment of mercury emissions inventories for the Great Lakes states

Anthropogenic mercury (Hg) air emissions for the eight Great Lakes states in 1999-2000 were evaluated by analyzing three inventories. The US Environmental Protection Agency (EPA) National Emissions Inventory (NEI) had the most complete coverage for all states, and total Hg emissions ranged from 4226 lb in Minnesota to 15,828 lb in Pennsylvania. Coal-fired electric utilities accounted for 52.7% of the region's Hg emissions, varying from 20.2% of the total in New York to 67.5% in Ohio. Other important contributors to regional emissions included municipal waste combustion (5.6%), mercury-cell chlor-alkali plants and hazardous-waste incinerators (4% each), stationary internal combustion engines (ICEs) (3.5%), industrial, commercial, and institutional (ICI) boilers (3.3%), and lime manufacturing (3.0%). Although medical waste incineration accounted for just over 1% of regional emissions using the original classifications, the inclusion of health care facilities that may have been inappropriately identified with other sectors would increase the sector to 4.5% of regional emissions (and decrease the stationary ICE sector to 1.4% of the regional total). There were substantial differences for some sectors between the NEI and the Great Lakes Regional Air Toxics Emissions Inventory (GLEI), as well as unexplained differences within inventories between states (particularly for the cement, lime, and asphalt industries, and for lamp breakage). Toxics Release Inventory data for 2000 mainly covered electric utilities, and differences from the NEI were significant for several states. An independent assessment indicates the possibility of underestimated Hg emissions by about twofold for ICI boilers, although data for the sector (in particular concerning fuel oil emissions) are highly uncertain. Limited data indicate the likelihood of significant underestimates of electric arc furnace mercury emissions in the NEI and GLEI inventories. Several measures are here identified for improving the reliability of the inventories, both for modeling of atmospheric transport and deposition modeling and for tracking progress in Hg reduction initiatives.