A model has been proposed for the scavenging of NO2 in a falling raindrop. After absorption, aqueous NO2 undergoes a second order reaction to form various ions such as NO2(-), NO3(-) and H(+). The model is based on the unsteady state convective diffusion equation, which was solved for given boundary conditions by using implicit alternate direction (ADI) method. The circulation of fluid inside and outside the raindrop has been taken into account to realistically describe the flow field in the numerical domain. The model predictions indicate that the pH of a raindrop is a direct function of the drop size and bulk concentration of NO2. The model predicted a pH of about 4.9 for a 100-micron raindrop falling through a 20-ppb ambient concentration of NO2. For the same ambient concentration of NO2, a 10-micron raindrop would have a pH of about 4.75. The predictions also suggested that for all practical purposes the gas phase resistance may be taken as the rate-controlling step. The predicted values of gas-side mass transfer coefficient compared well with the estimated values using standard mass transfer correlations.