This document describes the air quality modeling performed by EPA in support of the final rule to control emissions from new nonroad Spark-Ignition (SI) engines. A national scale air quality modeling analysis was performed to estimate the effect of the rule on future 8-hour ozone concentrations, future annual fine particulate matter (PM(sub 2.5)) concentrations, and future visibility levels. The inclusion of PM(sub 2.5) and visibility impacts represents an improvement on the modeling that was done for the proposed notice of rulemaking which only considered the impacts on ozone. An additional change from the modeling done at proposal was our use of the Community Multiscale Air Quality (CMAQ) model. The CMAQ model simulates the multiple physical and chemical processes involved in the formation, transport, and destruction of fine particulate matter and ozone. The 2002 version of the CMAQ modeling platform was used. 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 baseline emissions estimates, and a set of meteorological model inputs. The final Locomotive/Marine rule modeling analyses were also based on the 2002 CMAQ modeling platform.

EPA project officer: Patrick Dolwich. "May 2008." Final report. "EPA 454/R-08-005." PB2008-112827.