Abstract View
Acidity at the Nanoscale: pH Measurement of Individual Ultrafine Aerosol Particles
ZIYING LEI, Yao Xiao, Samuel Bliesner, Claire Mattson, Madeline Cooke, Nicole Olson, Julie Albert, Andrew Ault, University of Michigan
Abstract Number: 76
Working Group: Aerosol Chemistry
Abstract
Aerosol acidity (pH) is a critical property that affects the composition of the atmosphere as many key multiphase chemical reactions are pH-dependent. Despite the importance of atmospheric aerosol has been addressed, determining aerosol pH remain a challenge especially for ultrafine particles that have great impact on climate and health. Additionally, due to differences in particle-to particle composition, further understanding of atmosphere aerosol acidity at a single particle level is needed.
This study developed novel pH measurement methods for individual ultrafine aerosol particles. The first method was explored using a pH-sensitive polymer, poly(ε-caprolactone), to determine the acidity of particles. Acidic particles with pH 0 were deposited on a polymer thin film (21-25 nm), and the degradation of the polymer was characterized by atomic force microscopy and Raman microspectroscopy. As particle size decreased, polymer degradation increased, indicating an increase in aerosol acidity at smaller particle diameters. This method presents the potential of studying submicron individual aerosol particles without constraints on complex chemical compositions and relative humidity. Another pH measurement method was developed to directly measure the pH of individual ultrafine particles down to 68 nm in diameter using an acid-conjugate base approach via atomic force microscopy with photothermal infrared spectroscopy. Heterogeneity in pH values was observed for particles generated from the same solution, particularly as a function of size. Both pH measurement methods will improve the fundamental understanding of individual ultrafine aerosol acidity and fill the current knowledge gap of characterizing atmospheric aerosol particles.