Historical Comparison of Hazardous Air Pollutant Emissions from Aircraft, Commercial Marine Vessel, Locomotive and Other Nonroad Emission Sources Included in the National Emission Inventory

National hazardous air pollutant (HAP) emission inventories have been developed for the National Emissions Inventory (NEI) for 1990, 1996, and 1999. In developing aircraft, commercial marine vessels, locomotive, and other nonroad HAP emissions estimates for the 1999 NEI, all of the emission estimating methods were revised to incorporate better activity data (or fuel usage used as a surrogate for activity) and the latest emission factors or speciation profiles1. These improvements to the 1999 nonroad emission inventory were also applied to the 1990 and 1996 HAP emission inventories, making the inventories comparable and allowing for a historical comparison of HAP emissions throughout this period. This paper discusses the changes made to the nonroad HAP inventories, and evaluates the national emission trends for each source category. The paper will also quantify the significance that State-submitted data have in NEI, highlighting the need for states and local agencies to provide complete and accurate emission estimates for these source categories using comparable emission estimating methods. METHODOLOGY For the 1999 NEI, national emission estimates were developed for aircraft, commercial marine vessels, locomotives, and other nonroad engines and equipment. These national emission estimates were allocated t