This grant funds research by Michael S. Waring, Associate Professor of Architectural and Environmental Engineering and Peter DeCarlo, Associate Professor of Environmental Engineering and Chemistry at Drexel University, that will examine the chemical and physical transformations occurring within a heating, ventilation, and air conditioning (HVAC) system. Waring and DeCarlo’s work will focus on aerosol and gas-phase transformations, exploring how aerosol processing, composition, and component-based filtration are influenced by extreme and abrupt changes in temperature, relative humidity, and aerosol concentration as air is thermally conditioned and filtered. Utilizing a controllable HVAC system in a Drexel office building, Waring and DeCarlo will make seasonal measurements of the chemical composition of aerosols and trace gases at four locations in the HVAC system—outdoor, mixed, supply, and return air—to isolate the impact of HVAC system aerosol and gas composition. Aerosol composition will be measured using a high-resolution aerosol mass spectrometer with other instruments capturing trace concentrations of CO, CO2, H2O, O3, NO, NO2. Grant funds also support Waring and DeCarlo’s continued analysis of data collected during 2018’s Sloan-funded HOMEChem field project.