Methodologies for estimating emissions for the U.S. EPA's NOx SIP call, CER rule, and other complexities

Emissions inventories play an important role in many air quality decisions, and the importance of obtaining correct emissions data challenges the emissions inventory community to continuously improve its estimation techniques. The Clean Air Act Amendments of 1990 requires states with ozone nonattainment areas (NAAs) to submit periodically a comprehensive, accurate, and actual inventory of ozone precursor emissions until the areas are redesignated to attainment. They require the states with NAAs to report peak ozone season daily and annual estimates of the inventories for the counties that are in nonattainment. The recently proposed U.S. Environmental Protection Agency's (EPA) NO(x) SIP call and the Consolidating Emissions Reporting (CER) rule are more demanding still. The CER rule requires the states to report statewide point source inventories, 3-yr cycle inventories, and NO(x) SIP call inventories by county for all source types, regardless of the attainment status; the estimating periods are peak ozone season daily, 5-month ozone season, and annual estimates. Furthermore, complexities in emissions inventories such as estimating the emissions with different seasonal and multiple controls exist. These complexities and methodologies for estimating emissions for different time periods are not addressed sufficiently either by the EPA's procedure manuals or by the Emissions Inventory Improvement Program guidance documents. This paper presents methodologies for estimating emissions for different time periods and multiple controls. These methodologies will help the EPA, state, and local government agencies to meet the evolving demands of emissions inventories and the reporting requirements of the NO(x) SIP call and the CER rules.