Air Quality Modeling Final Rule Technical Support Document

In this technical support document (TSD) authors describe the air quality modeling performed to support the Final Transport Rule (TR). For this rule the Environmental Protection Agency (EPA) used air quality modeling to:

1. identify locations expected to be nonattainment or have maintenance problems for annual (average) PM2.5, 24-hour PM2.5, and/or 8-hour ozone for the analytic years chosen for the TR,
2. quantify the impacts (i.e., air quality contributions) of SO2 and NOX emissions from upwind states on downwind annual and 24-hour PM2.5 concentrations at monitoring sites projected to be nonattainment or have maintenance problems in 2012 for the 1997 annual and 2006 24-hour PM2.5 NAAQS2, respectively,
3. quantify the contributions of NOX emissions on downwind 8-hour ozone concentrations at monitoring sites projected to be nonattainment or have maintenance problems in 2012 for the 1997 ozone NAAQS from upwind states,
4. “calibrate” the Air Quality Assessment Tool (AQAT) for use in the process of determining the amount of significant contribution,
5. examine issues related to the need for NOx emissions reductions from upwind states, and
6. assess the health and welfare benefits of the emissions reductions expected to result from this rule.

This TSD includes information on the following analytical aspects of the TR air quality modeling:

• a description of the modeling platform,
• an evaluation of model predictions compared to measured concentrations,
• the procedures and results of projecting ozone and PM2.5 concentrations for future year scenarios,
• the procedures used to quantify interstate contributions for annual and 24-hour PM2.5, and 8-hour ozone,
• the results of evaluating the interstate contributions using concentration thresholds, and 
• the air quality impacts from the SO2 and NOX emissions reductions expected from the “Air Quality-Assured Trading” scenario (i.e., remedy scenario), as described in the rule preamble.