This team is recognized for the design and development of a robust, SI-traceable, photocatalytic activity measurement system, which includes a new international documentary standard and a new value assignment to NIST Standard Reference Material 1898, Titanium Dioxide Nanomaterial. These measurements and standards enable quantitative assessments of the risk associated with consumer and biological applications of nanomaterials that have photocatalytic activity. This important measurement scale can be deployed globally to facilitate measurement agreement between international bodies.