Carbon Quantum Dots for Direct Measurement of the pH of Aerosol Particles
KOMAL JASWAL, Victoria Adekunle, Miriam Freedman, The Pennsylvania State University
Abstract Number: 249
Working Group: Instrumentation and Methods
Abstract
Continental aerosol particles have been predicted to be highly acidic based on their composition and thermodynamic models. The acidity of aerosol particles can have a significant impact on atmospheric visibility, climate, heterogeneous chemistry, human health, and biogeochemical cycles. The small size of aerosol particles makes pH measurement challenging. Here, we present a novel approach using carbon quantum dots (CQDs) as in situ fluorophores to directly measure the pH of individual droplets and droplet phases in the range of pH 1.5 – pH 3.5. The method involves two different types of CQDs, where orange emissive CQDs serve as an internal standard and blue emissive CQDs serve as the pH-sensitive probe. A calibration curve was constructed using the ratiometric fluorescence intensities of droplets of standard solutions to develop an assay of fluorescence emission intensities as a function of pH. The calibration curve was then used to determine the pH of model continental aerosol particles in the highly acidic range and to determine the effect of organic compounds of different pKa values on the droplet pH. Our method demonstrates the capability of CQDs for real-time and direct measurement of the acidity of aerosol particles and their phases and thus provides an avenue to enhance our understanding of the physicochemical properties of atmospheric aerosol particles. The ability to directly determine aerosol pH holds a significant potential to parameterize thermodynamic models and refine predictions of aerosol properties.