This document describes the 2002-Based Air Quality Modeling Platform (2002 Platform) used by EPA in support of the Ozone National Ambient Air Quality Standard (NAAQS) Final Rule Regulatory Impact Assessment (RIA). A modeling platform is a structured system of connected modeling-related tools and data that provide a consistent and transparent basis for assessing the air quality response to changes in emissions and/or meteorology. A platform typically consists of a specific air quality model, base year and future year emissions estimates, a set of meteorological inputs, and estimates of 'boundary conditions' representing pollutant transport from source areas outside the region modeled. We used the Community Multiscale Air Quality (CMAQ)(sup 1) as part of the 2002 Platform to provide a national scale air quality modeling analysis for the RIA. The CMAQ model simulates the multiple physical and chemical processes involved in the formation, transport, and destruction of ozone and fine particulate matter (PM2.5). The 2002 base year and 2020 future base case emissions scenarios, which were developed as part of the Platform, were used in support of the RIA modeling. In brief, the 2020 base case inventory includes activity growth for some sectors, and controls including: the Clean Air Interstate Rule, the Clean Air Mercury Rule, the Clean Air Visibility Rule, the Clean Air Nonroad Diesel Rule, the Light-Duty Vehicle Tier 2 Rule, the Heavy Duty Diesel Rule, known plant closures, and consent decrees and settlements.