The simple and precise model for the estimation of rain acidity from the ambient $SO_2$ concentration was developed using the wet scrubbing theory and the chemical equilibria of $SO_2$, $CO_2$ and $H_2O$ system.
From the developed mixing height equation, and the relationship between NTU (=number of transfer units) and the concentration of $SO_2$(aq) in rain drops, the average overall volumetric mass transfer coefficient ($\hat{k}_{OL}.a$) of $SO_2$ system was estimated using the observed aqueous $SO_2$ concentration in rain drops, ambient $SO_2$ concentration, and a average mixing height. In Seoul, Korea where the effect of $SO_2$ on rain acidity is as high as 84% and the average mixing height is 1 km, the average $\hat{k}_{OL}.a$ a of $SO_2$ system was to be 0.379 moles/hr.㎥.
The important parameters affecting the rain acidity were identified as mixing height, rainfall intensity, and ambient $SO_2$ concentration, and their effects on the values of acidity were quantified.
The correlation between the observed and estimated rain acidity using developed model had satisfiable results, and the correlation coefficient was 0.438 and the ratio estimated rain acidity to observed rain acidity was 1.123.
