Comparison of Aerosol Acidity Based on a Direct Measurement Method and a Chemical Thermodynamic Model

Aerosol acidity is an important parameter in aerosol science that affects many chemical reactions in the atmosphere, and it is often estimated using chemical thermodynamic models. The Extended Aerosol Inorganic Model IV (E-AIM IV) is frequently used for this purpose; however, due to the limited number of available direct measurement methods of aerosol acidity, there is still a certain degree of uncertainty with regard to how accurately the simulation results reflect reality. In this study, a new pH testing paper method for the direct measurement of aerosol pH is used to measure the pH (pHmeas) of aerosol particle samples. Based on the data of the ionic constituents of the samples, the E-AIM IV model is then used to estimate aerosol pH (pHest). This study provides a comparison of pHmeas and pHest, revealing that the relationship is satisfactorily approximated by a simple linear regression of pHest = 1.05pHmeas + 0.38 (R2 = 0.90). The strong correlation and slope very close to unity indicate that the pH testing paper method corroborates the outputs of the E-AIM IV model.