Colorimetric particle acidity analysis of secondary organic aerosol coating on submicron acidic aerosols

Abstract

The particle acidity of secondary organic aerosol (SOA) created from ozonolysis of α-pinene in the presence of acidic inorganic seed aerosols was investigated using an indoor Teflon film chamber. Colorimetry integrated with a reflectance UV-Visible spectrometer was used for the first time to dynamically measure the aerosol acidity over time. An external calibration curve was produced based on the correlation between the proton mass (ng) collected on the filter, which was impregnated with metanil yellow, and the absorbance of the reflectance UV-Visible spectra for the protonated and the unprotonated metanil yellow on the filter. Using this calibration curve, the particle acidity of the submicron acidic sulfate aerosol coated with SOA was measured from the reflectance UV-Visible spectra of filter samples. The colorimetric analysis requires a short sampling time (less than 2 m) for SOA studies using the laboratory Teflon film chamber and eliminates extraction of the filter sample with water. Results show that the particle acidity of the aerosol decreased over time due to the formation of organic sulfate through the interaction of sulfuric acid with SOA products. The feasibility of this method is also demonstrated for the measurement of the acidity of ambient particles. Copyright © American Association for Aerosol Research.