Outdoors, strong ultraviolet light from the sun drives the photolysis of ozone, resulting in the production of hydroxyl (OH) radicals. Hydroxyl radicals, sometime referred to as “nature’s vacuum cleaner” are highly reactive and short lived. They can react with volatile organic compounds leading to the formation of peroxy radicals. These radicals, in turn, react rapidly with a range of compounds, eventually producing secondary organic aerosols in the atmosphere. Yet much is unknown. Despite the absence of the strong ultraviolet light that drives oxidation reactions outdoors, there is preliminary evidence that indoor environments contain hydroxyl radicals. The pathways that generate these radicals and the role they play in indoor chemistry are mysteries. Funds from this grant support an effort by Philip S. Stevens (Indiana University), in collaboration with Brandon Boor (Purdue University), to examine radical concentrations and associated aerosol production in indoor environments. The team aims to improve our understanding of oxidation chemistry in indoor environments through comprehensive measurements of radical concentrations, including their sources and sinks, as well as the impact of radical concentrations on aerosol production in several laboratories, chambers, and at least one residence. The results of the studies will be shared through peer-reviewed journals and through presentations at meetings of the International Society of Indoor Air Quality and Climate, the American Chemical Society, and the American Association for Aerosol Research. At least four students will be trained.