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Direct Measurement of the pH of Aerosol Particles
EMMA TACKMAN, Miriam Freedman, The Pennsylvania State University
Abstract Number: 82
Working Group: Aerosol Chemistry
Abstract
The level of acidity in aqueous aerosol particles found abundantly in the atmosphere has wide ranging effects on a variety of chemical processes from reaction rates to cloud formation but remains poorly characterized. Determining the pH of aerosol particles is difficult due to their small size, so indirect measurements and thermodynamic models have been used despite shortcomings, such as imprecise modeling constraints. Here, we present a new method for directly assessing aerosol particle acidity using carbon quantum dots as a novel in situ fluorophore. Carbon dots are easy to synthesize and are sensitive to pH in the highly acidic regime relevant to ambient aerosol particles. For this study, carbon dots were synthesized in house using a commercially available microwave oven and shown to be indefinitely shelf stable. Our results support the effectiveness of using this fluorophore in previously characterized model systems and proxies for a variety of environmentally relevant aerosol particles. The pH of a series of aerosolized buffered solutions were measured to establish the method. Additionally, the pH of particles containing a complex organic mixture (COM) more representative of environmental aerosols was also determined, proving the efficacy of carbon quantum dots as pH-sensitive fluorophores. The ability to directly measure the pH of aerosol particles and populations will help to parametrize models and improve projections for other aerosol properties and their influence in the atmosphere.