This document describes chemical and physical processes important to the formation of ground-level O3, PM2.5, visibility, and deposition in the context of modeled long-range transport assessments for permit review programs. Chemical transport models that characterize these processes include both Lagrangian, which typically only have a single-source included in the model, and photochemical grid models that include some representation of all anthropogenic, biogenic, and geogenic sources. Modeling systems appropriate for the purposes of estimating long-range transported single-source secondary impacts are described, and recommendations are made with respect to the use of certain types of modeling systems for this type of application. Model evaluation is important to ensure that a particular system is fit for the purpose of estimating long-range single-source secondary impacts. One aspect of this type of evaluation for long-range transport assessments would be demonstrating model skill in meteorological processes important for long distance transport by replicating appropriate mesoscale tracer release experiments. In addition to establishing whether a modeling system is generally appropriate for this purpose, project specific evaluations that compare model estimated meteorology and chemical estimates with measurements near the project source and key receptors is also an important model evaluation component.

Project officer: Kirk Baker Revision of EPA-454/P-15/003 Includes bibliographical references (pages 20-23). "EPA-454/R-16-002." "June 2016."