AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Measurement of Aerosol Acidity Using Colorimetry Integrated with a Portable Miniature UV-Visible Spectrometer
RYAN WINSLOW, Myoseon Jang, University of Florida
Abstract Number: 360 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosol acidity is an important characteristic of inorganic aqueous salts. It influences the health effects of particulates due to metal solubility, and is also a kinetic model parameter that processes acid-catalytic reactions of atmospheric organics to increase secondary organic aerosols. Despite numerous usages, the conventional measurement of aerosol acidity is limited to indirect estimations using a thermodynamic model and the compositions of ionic species originating from ion chromatography. In this study, a method for measuring aerosol acidity has been developed using colorimetry integrated with reflective UV-visible spectrometry (C-RUV). In order to assemble a portable device in the field, we use a miniature spectrometer that is self-contained and deployable. The C-RUV system operates by passing an air sample through a filter infused with an indicator (metanil yellow), which changes color in response to acidity changes. The optical probe transfers both the source beam from the spectrometer to the filter surface via optical fiber, and the reflected beam from the filter to the detector in the spectrometer. The C-RUV method has been applied to measure the proton concentration of inorganic aerosols comprised of ammonium and sulfate under various humidity conditions. Inorganic aerosols were introduced into a flow tube from an atomizer, and collected on the colorimetric filter. The color change of the particle sample was measured in situ by exposing the filter to the optical probe at different humidities, which were controlled using a water bubbler and dry air. The humidity effect on the equilibrium thermodynamics of the indicator (protonated vs. unprotonated) in response to aerosol acidity at different ionic strengths was theoretically described by the inclusion of excess acidity (X) in the calibration curve. The feasibility of this method and the resulting calibration curve was also demonstrated by measuring the acidity of ambient particles.