This grant supports research by atmospheric chemist Allen Goldstein and environmental engineer William Nazaroff to examine the processes controlling abundance, sources, and fates of organic chemicals indoors. The work will focus on the roles of human occupants, emissions from the building and its contents, and the intrusion of outdoor pollutants as agents influencing indoor air chemistry. In a series of experiments, Goldstein and Nazaroff will characterize organic compound composition of the air in residential spaces, cataloging the relative abundance of volatile (VOC), intermediate volatile (IVOC), and semivolatile (SVOC) organic compounds in both the gas and particle phases, and to compare this composition with outdoor air. They will then analyze how organic compound composition changes across various dimensions: by time, by location inside the residence, and by human occupancy. Their methods will enable them to apportion indoor air organics into major source categories: building fabric and contents, occupants and activities, and outdoor air, with the ultimate objective of understanding the role of emissions influencing indoor air chemistry. This work will advance the state of knowledge regarding the contributions of humans, human activities, surface interactions, and oxidation processes influencing indoor air composition in residences. This new knowledge will be shared through peer-reviewed publications and presentations at conferences and meetings. At least three students will be trained.