Comparison of Nonroad Hazardous Air Pollutant Emissions Included in the National Emission Inventory

The National Emission Inventory (NEI) includes criteria pollutants and hazardous air pollutants (HAPs) from all stationary and mobile sources. The mobile source emissions component of NEI contains estimates for onroad as well as nonroad source categories. Nonroad source categories include, aircraft, commercial marine vessel (CMV), locomotive, and “other ” nonroad vehicle and engines1. The other nonroad source categories are the vehicles and engines included in U.S. Environmental Protection Agency’s (EPA’s) draft NONROAD model, such as construction and agricultural equipment, recreational engines, and portable commercial, institutional, and industrial equipment. The nonroad emission estimates have been significantly improved in the 1999 NEI, both in terms of the quality of the emissions estimates which were developed and the refinement of the spatial allocation methods used. This paper discusses the methods used and improvements made to estimate emissions for the other nonroad emission sources. This paper also compares the emission estimates between each of the individual other nonroad categories, identifying the most significant sources of the HAPs included in the NEI. Spatial assessments are performed to evaluate emission differences between urban and rural counties.