Characterization of the pH of Organic/Inorganic Aerosol Using Ratiometric Fluorescence Imaging

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The Environmental Chemical Sciences Program in the Division of Chemistry funds Professor Miriam Freedman for this project which is focused on the acidity of aerosols. This property of aerosol particles impacts chemical reactions in the atmosphere as well as human health. Based on the composition of aerosol particles and gas-phase molecules, the acidity of aerosol particles can be estimated using models. These models predict that aerosol particles are highly acidic, but results differ depending on the model used. This project aims to develop a novel direct measure of aerosol acidity using carbon quantum dots. Using this approach will make it possible to explore the molecular origins of the high acidity of aerosol particles for both marine and continental environments. Further development of the probes will enable applications in atmospheric chemistry studies or in other fields where highly acidic samples are of interest. This project has potential for technology transfer, provides training for undergraduate and graduate students, and supports dissemination to the public through outreach events.To study the acidity of aerosol particles, this project will use ratiometric fluorescence imaging of carbon quantum dots. Currently, the Freedman research group has developed a probe that covers the pH range of 0 – 3.5. To determine the origins of the high acidity of continental and marine aerosol, the pH of model systems of organic compounds with salts will be characterized. Ammonium sulfate will be used for model continental aerosol and sodium chloride will be used for model marine aerosol. The organic compounds are chosen to be relevant for the specific type of aerosol as well as to have a range of pKa values, a range of complexities in composition from single organic compounds to mixtures, and a range of surface activities. To develop the probe further, the project aims to increase the pH range that can be measured, incorporate an internal standard, and deposit the probe on substrates.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.