Funds from this grant support a team led by Brent Williams of Washington University in St. Louis to improve our ability to collect and analyze indoor air samples through the development of a chemically resolved volatility and polarity separator. The project aims to build and test a new field-deployable automated instrument for the simultaneous measurement of organic gas and particle chemical composition. The work plan has three parts. First, Williams and his team will develop a modified volatility and polarity separator capable of detailed chemical characterization of the particle phase and gas phase of airborne indoor organic material. Next they will demonstrate the strengths of the new measurement capacity through controlled laboratory studies and through an indoor field study. Last, they will develop an open-access volatility- and polarity-separated chemical profile database of indoor sources and transformations, along with open-access data analysis codes for use by the indoor air research community. Predicted outcomes of this project include the new instrument, the open access data base, and new knowledge about the composition of indoor air. The team plans to share their findings through multiple peer-reviewed publications and conference presentations on instrument development and through open-access chemical databases and analysis codes. One postdoctoral fellow and three graduate students will be trained.