Analysis of Hygroscopic Growth Models with Different Water Activity Estimation Models for Urban Aerosols

In this paper, the radii and the volume mix ratios of Urban aerosols were extracted from Optical Properties of Aerosols and Clouds (OPAC 4.0) at Relative Humidies of 0, 50, 70, 80, 90, 95, 98 and 99. The compositions of urban aerososl in OPAC 4.0 are water solubles (waso) insoluble (inso) and soot. A sensitivity analysis was carried out examining the sensitivity of effective hygroscopic growth and water activity as modeled with the Köhler equation. The effective radii and the effective hygroscopic growths were determined and applied to the Kohler theorem to determine the water activity and Kelvin effects. Different concentrations of aerosols were used in the Köhler equation. After applying Kohler theorem, it was discovered based on the values of the significance that, water activities dominate the Kelvin effects. To determine effective hygroscopic growth models with different water activity estimation models, three water activity models were applied, and these models are, Activity Parameterization (AP), Van’t Hoff factor (VH) and Effective hygroscopicity parameter (EH) models. The coefficient of determination (R2), was used to determine the best model(s). From the analysis of the three models, it can be concluded AP model out perform all the models with R2 ranging from 0.9999792 to 0.9999929 for soot,0.9999792 to0 .9999850 for waso, and 0.9999792 to 0.9999949 for inso, while that the VH models fit, of Frank et. al., (2007), both linear and quadratic become the second with R2, ranging from 0.999692 to 0.999797 for soot, 0.999692 to 0.998879 for waso and 0.999692 to 0.999541 for inso.