Antimicrobial chemicals, called quaternary ammonium compounds (QACs), are commonly used to clean indoor spaces. QACs stay behind on surfaces for different lengths of time and are reactive. Their chemical structure, toxicity, and their fate in the indoor space may change over time. This project will measure the chemical reactions involving QACs in model indoor environments to understand the rates of reactions and the products that form. The study will also model where the newly formed chemicals might travel indoors and their toxicity to humans. The results of the project will help design safer cleaning methods to use in various indoor environments, which will support improved health for Americans. Quaternary ammonium compounds (QACs) are a class of chemicals in commercial products such as surfactants, anti-microbial agents, and emulsifiers. These chemicals have negative health impacts in the form of skin irritation and work-related asthma, and there is growing concern about the role they play in antimicrobial resistance. This project will measure the oxidation kinetics and reaction products formed for representative QAC compounds due to atmospheric aging processes indoors. The products are important because they may have different behaviors and health impacts compared to the starting compounds. The project focuses on heterogeneous oxidation of QAC-containing aerosol particles and indoor surface films. The study will evaluate the oxidation of representative QAC compounds us