Aerosol Acidity Measurement Using Colorimetry Coupled With a Reflectance UV-Visible Spectrometer

Abstract

In this study, aerosol acidity was measured using colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV). An inorganic aerosol comprising NH4 +−H+−SO4 2−−H2O was generated using an atomizer and introduced into a 2-m3 indoor Teflon film chamber. The produced aerosol was collected on the Teflon-coated glass fiber filter dyed with metanil yellow (MY) as an indicator for measuring proton concentrations in aerosol. A calibration curve for measuring aerosol acidity using the C-RUV technique was obtained through the relationship between the absorbance of the UV-Visible spectrum of the filter sample vs. theoretically calculated proton concentrations using the E-AIM Model II. To develop the C-RUV method under various humidities, the aerosol filter sample was mounted inside a small optical flow chamber controlled for humidity in situ. The humidity effect on the equilibrium thermodynamics of the indicator was theoretically described by inclusion of excess acidity (X) into the calibration curve. Th...