Quaternary Ammonium Compounds: lifetimes and chemical fates in indoor environments

About This Grant

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 using OH radicals and/or ozone to test the hypothesis that condensed phase radical cycling in aerosol particles and indoor surface films increases the oxidation rate of QACs except when the other chemicals in the mixture form a more viscous film that protects the QAC. The loss of the QACs and the formation of products will be measured using Liquid Chromatography/Mass Spectrometry and Gas Chromatography/Mass Spectrometry. The fate of the QACs and their products will be modeled indoors using mass balance and estimates of partitioning constants in different indoor compartments. By measuring loss rates and products in representative indoor environments, the study will provide an extensive picture of the lifecycle of QACs. The outcomes of this work could lead to recommendations for optimum QAC structures and cleaning methods that meet the needs for cleaning but minimize impacts on human health and the environment. The project will support development of learning modules in a large undergraduate class at the University of Michigan that focuses on mass balance. These will include lecture materials, a classroom demonstration, and online materials that introduce students to modeling software and guide them in implementing the tools to generate a model of pollutant persistence indoors. These educational tools will be published in an educational journal for Environmental Engineering and Environmental Chemistry undergraduate instruction. The activities will contribute to a future workforce in STEM in the United States. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.