This grant funds a research project by atmospheric photochemist D. James Donaldson, professor at the University of Toronto, and Christian George, a senior scientist at France’s National Center for Scientific Research (CNRS) in Lyon, France to investigate the role of photochemistry indoors. The team plans to establish whether heterogeneous (gas/surface) photochemical reactions occur indoors, producing gas phase oxidants and their precursors, as well as particles. The team plans to address three main questions: (1) Are indoor surfaces of occupied spaces photochemically active in the formation of gas phase oxidants? (2) If so, how do local variables (temperature, relative humidity, specifics of illumination) affect the formation of gas phase oxidants? (3) Is heterogeneous photochemistry a source of indoor particulate matter? These questions will be addressed through a series of laboratory and chamber experiments in both laboratories in Toronto, Canada, and Lyon, France. To facilitate the long-distance collaboration, the team will conduct a series of two-way student exchanges, as well as annual meetings between the principal investigators in Toronto and Lyon. This exchange of students will encourage and support strong international scientific ties at all levels, allowing students to experience different societies and laboratory structures, and better preparing them for transnational activities in the future. This project promises to provide new knowledge about indoor photochemistry. The results will be shared through peer-reviewed publications and presentations at conferences and meetings. At least three undergraduate students, three graduate students, and two postdoctoral fellows will be trained.