The Acidity Distribution of Drops in a Deep Convective Cloud

Abstract

AbstractA cloud model with detailed bin microphysics as well as aqueous‐phase chemistry is used to investigate how the acidity distribution of drops changes in a deep convective cloud. The results show that the concentration of hydrogen ion is higher in the relatively large droplets at the initial stage of the cloud, whereas it has an opposite dependence on the drop size at the later stage of the cloud. The spectrum distribution of drop acidity also highly varies with space, reflecting the different effects of macrophysical and microphysical processes on drop acidity. For the entire simulation period, evaporation process contributes the most to the decrease in pH values of drops, which is related to the decrease in cloud water. Condensation and collision‐coalescence play an important role in modifying the chemical rates of hydrogen ion production, leading to changes in the pH values. In addition, both higher concentration of sulfur dioxide and enhanced aerosol loading lead to lower pH values of drops, but the differences in pH values under different aerosol loadings vary with time and space, which is associated with the different contribution of microphysical processes. The sensitivity tests reveal that the changes of pH values by varying aerosol loadings could have a significant impact on sulfuric acid production through aqueous oxidation of sulfur dioxide.