Surface-to-volume ratios are orders of magnitude larger indoors compared to outdoors. As a result, air-surface interactions play a significantly more important role in indoor chemistry than in typical atmospheric chemistry.  This grant provides ongoing support for the work of surface chemist Vikki Grassian of the University of California, San Diego to examine the fundamental chemistry of indoor surfaces. Using a variety of techniques, including X-ray photoelectron spectroscopy, vibrational spectroscopy, and atomic force microscopy, Grassian and her team will observe and analyze the interactions between gases and particles, on the one hand, and various surfaces commonly found indoors, on the other.  The team’s focus will be on better understanding the fundamental mechanisms of reaction chemistry, including oxidation reactions, surface reactions of chlorine-containing cleaning products, and nitrogen oxide chemistry that leads to the formation of nitrous acid. Grassian’s experiments have been designed with an eye toward ensuring collected data can be usefully integrated into existing models of indoor air chemistry.   This project will result in new knowledge on the fundamental chemistry that occurs on indoor surfaces and new data for input into indoor air quality models. The results will be shared through peer-reviewed publications and presentations at conferences and meetings, with at least two students and one postdoc being trained.