Acknowledgments
This research was funded and conducted by the National Risk Management Research Laboratory of U.S. Environmental Protection Agency (EPA), Cincinnati, OH. This paper has not been subjected to internal policy review of the U.S. EPA. Therefore, the research results do not necessarily reflect the views of the agency or its policy. Mention of trade names and commercial products does not constitute endorsement or recommendation for use. The authors are thankful to Dr. Ratandeep Kukreja for HR-TEM and SEM measurements, and Ms. Geshan Zhang for providing radical production analysis.