Air Quality Modeling Technical Support Document for the Final Cross State Air Pollution Rule Update

This technical support document (TSD) describes the air quality modeling performed to support the final Cross State Air Pollution Rule for the 2008 ozone National Ambient Air Quality Standards (NAAQS). In this document, air quality modeling is used to project ozone concentrations at individual monitoring sites to 2017 and to estimate state-by-state contributions to those 2017 concentrations. The projected 2017 ozone concentrations are used to identify ozone monitoring sites that are projected to be nonattainment or have maintenance problems for the 2008 ozone NAAQS in 2017. Ozone contribution information is then used to quantify projected interstate contributions from emissions in each upwind state to ozone concentrations at projected 2017 nonattainment and maintenance sites in other states (i.e., in downwind states).
The remaining sections of this TSD are as follows. Section 2 describes the air quality modeling platform and the evaluation of model predictions using measured concentrations. Section 3 defines the procedures for projecting ozone design value concentrations to 2017 and the approach for identifying monitoring sites with projected nonattainment and/or maintenance
problems. Section 4 describes (1) the source contribution (i.e., apportionment) modeling and (2) the procedures for quantifying contributions to individual monitoring sites including nonattainment and/or maintenance sites. Section 5 includes an analysis of the contributions captured at alternative thresholds.