EPA is approving revisions to the Maryland State Implementation Plan (SIP) which pertains to the 1990 base year emission inventory for the marginal and severe ozone nonattainment areas within the state. The ozone nonattainment areas consist of the counties of Cecil, Ann Arundel, Baltimore City, Baltimore, Carroll, Harford, and Howard (all severe); Queen Anne's and Kent (both marginal). The SIP was submitted by the Maryland Department of the Environment (MDE) for the purpose of establishing the 1990 baseline emissions contributing to the ozone nonattainment problems in Maryland. This action is being taken under section 110 of the Clean Air Act.