Influence of Water Soluble and Relative Humidities on the Kelvin Effect and Water Activities of Urban Aerosols

Abstract

The study used the Optical Properties of Aerosols and Clouds (OPAC 4.0) database to obtain the microphysical characteristics of urban aerosols and performed numerical analyses of the analytical formulas describing how equilibrium relative humidity (RH), effective radius, hygroscopic growth, and the corresponding absolute and fractional changes in these parameters respond to surface-tension influences (Kelvin effect) on atmospheric aerosols. It was determined that the Kelvin effect increase with the increase in water soluble and RH, and for the water activity it increased with the increase in RH but decreased with the increase in water soluble. The three models analyzed, are, two of one parameter models and one of three parameters model. The analysis of the extracted data shows that, to first-order accuracy, variations in equilibrium RH, effective radius, and effective hygroscopic growth are influenced by aerosol composition. Results from all three models further indicate that the fractional changes in ambient RH, effective radius, and hygroscopic growth likewise depend on the aerosol makeup. Overall, the study found that the strength of the Kelvin effect and its resulting impact on atmospheric aerosols is determined by the hygroscopic properties of the aerosols.  For lower RHs, (50 and 70) the range of the over estimations of the effective hygroscopic growth and effective radii are less that 1%. As RH increases, the degree of overestimation also rises following a power-law relationship with RH. This indicates a growing deviation from ideal behavior at higher RH, likely due to the electrolytic characteristics of the ionic aerosol mixtures. Consequently, more complex formulations are needed to maintain accuracy at elevated RH levels. Overall, these findings underscore the importance of applying Kelvin corrections when modeling effective hygroscopic growth and effective radii of atmospheric aerosols, particularly under high-RH conditions.