AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Calibration of C-RUV Aerosol Acidity Measurement Using Two Inorganic Thermodynamic Models and Its Application to Field Data
SHIQI SUN, Myoseon Jang, Sanghee Han, Chufan Zhou, Ryan Winslow, University of Florida
Abstract Number: 654 Working Group: Air Quality Sensors: Low-cost != Low Complexity
Abstract Despite numerous studies that report the association of aerosol acidity with health effects of particulates and aerosol chemistry, the accuracy in measuring aerosol acidity is uncertain. In a typical aerosol sample applied to a measurement of the concentration of proton ([H+] mol/L of aerosol), the collected aerosol is extracted with water to analyze ion species with ion chromatography (IC). Then, an inorganic thermodynamic model with IC data determines [H+] in aerosol. However, non-ideality associated with activity coefficients of ionic species in aerosol is dissimilar from that in dilute aqueous solution. Most data reported in the literatures are produced in highly humid aerosol or highly acidic sulfate-rich aerosol. Therefore, the prediction of [H+] by inorganic thermodynamic models is also hampered by the uncertainty in database. Our laboratory’s recent research efforts have improved the state-of-the science-art via the development of colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV) by avoiding the use of solvents. In this study, [H+] measurement by the C-RUV is calibrated for sulfate-rich inorganic aerosols where the uncertainty in inorganic thermodynamic models is low to predict [H+]. The two calibration equations for C-RUV data are obtained using two different inorganic thermodynamic models, E-AIM and ISORROPIA. Then, calibration equations are extrapolated to ammonia-rich aerosols where the thermodynamic models poorly perform. [H+] determined using C-RUV data is deviated from the prediction using both models, although less with E-AIM. C-RUV is also applied to ambient data collected in Gainesville, Florida. Overall, aerosol acidity is high (pH < 1) in summer while it is low (1 > pH > 3) in winter due to the condensation of ammonia gas to aerosol at low temperature.