This grant funds research by Professor William Nazaroff, an expert on the physics and chemistry of indoor air pollutants, and Professor Allen Goldstein, an expert on anthropogenic and natural contributions to the chemical composition of the atmosphere. The researchers are working to expand the understanding of processes controlling abundance, sources, and fates of organic chemicals indoors, focusing on the roles of human occupants as agents influencing indoor air chemistry. Over a several-week period, the researchers will monitor the indoor air of a residence under five conditions: (a) house vacant, emphasis on spatial resolution; (b) house vacant, emphasis on temporal resolution; (c) house normally occupied, emphasis on spatial resolution; (d) house normally occupied, emphasis on temporal resolution; and (e) manipulation experiments, such as cooking, cleaning, or dishwashing. Monitoring will focus on detecting several important chemicals, including volatile organic compounds (VOCs), nitrate radicals, nitrogen oxide trace gases, carbon dioxide, and ozone. In addition, the team will sample environmental conditions such as temperature, relative humidity, ultrafine particulate concentration, and air exchange rates. Samples will then be analyzed to try to apportion VOC chemical concentrations in sampled indoor air to their sources, including outdoor air, building-associated sources present when the residence is vacant, occupant-associated sources, and secondary production from indoor chemical reactions. This project will generate important new insights into indoor chemistry, which will be shared through peer-reviewed publications and presentations at conferences and meetings. At least three students will be trained during the course of the project.