The EPA is developing scientific and technical documents associated with the Ozone National Ambient Air Quality Standard (NAAQS). The Ozone NAAQS Federal Reference Method (FRM) serves as the standard protocol for measuring ambient Ozone concentration values. The Ozone NAAQS FRM is used to assess whether a given geographic region is in full regulatory compliance with the appropriate Ozone NAAQS standard. It is also used to help assess the operational and laboratory-based performance of emerging monitoring technologies. The current Ozone NAAQS FRM (Ethylene-Chemiluminescence method) is no longer being manufactured, and the EPA’s Office of Research and Development (ORD) is proposing addition of the Nitric Oxide (NO)-Chemiluminescence method as a second FRM for Ozone. ORD has requested CASAC review of the scientific and technical aspects of a draft document that supports recommendation to adopt the NO-Chemiluminescence method as a second FRM for measuring ozone.