The USEPA is approving the ozone State Implementation Plan (SIP) revision and redesignation requests submitted by the State of Ohio for the purpose of redesignating Franklin, Delaware, and Licking Counties (Columbus area) from marginal nonattainment to attainment for ozone; and revising Ohio's SIP to include a 1990 base-year ozone precursor emissions inventory for the Columbus ozone nonattainment area. Ground-level ozone, commonly known as smog, is an air pollutant which forms on hot summer days which harmfully affects lung tissue and breathing passages. The redesignation to attainment of the health-based ozone air quality standard is based on a request from the State of Ohio to redesignate this area and approve its maintenance plan, and on the supporting data the State submitted in support of the requests. Under the Clean Air Act, designations can be changed if sufficient data are available to warrant such change, and a maintenance plan is put in place which is designed to ensure the area maintains the ozone air quality standard for the next ten years. The emissions inventory was submitted to satisfy a Federal requirement that States containing ozone nonattainment areas submit inventories of actual ozone precursor emissions for the year 1990. Data from emission inventories aide States in developing plans to meet and/ or maintain the ozone air quality standard.