This document presents the approaches EPA used to conduct the 2005 NATA, including descriptions of how:

• emissions data are compiled and prepared for use as model inputs,
• ambient concentrations of air toxics are estimated,
• exposures to air toxics for populations are estimated,
• toxicity values are selected and assigned to chemicals,
• human health risks and hazards are characterized, and
• variability and uncertainty are addressed.

Specifically, this document summarizes the data sources, methods, models, and assumptions used in NATA that have been published in various EPA reports and have been available on the various NATA assessment web sites.

• An Overview of Methods for EPA's 2005 NATA (PDF)(220 pp, 3 MB, Jan. 31, 2011)