The Clean Air Act Amendments of 1990 require that EPA conduct a study to determine the contribution of nonroad equipment to the emission inventories of selected nonattainment areas. The contribution is determined by the population of nonroad equipment in a given area, the average load factor at which the equipment's engine is used, the average annual hours of use of the equipment, the horsepower of the engine, and the emission factor attributable to the engine. Since a nonattainment area is a conglomeration of counties within a state, or across states, it is necessary to estimate the county level equipment populations. Engine sales data or equipment population data, however, are not available at the county level, but only at the national and state level. Therefore, a methodology that distributes equipment populations from these levels of aggregation to the county level must be developed. The report presents EEA's methodology to estimate equipment populations for the 24 nonattainment areas included in EPA's study. The report also presents national data on load factors, annual usage, and horsepower.

"September 30, 1991." Prepared for the U.S. Environmental Protection Agency. Microfiche.