This article concerns the modeling of the SO2 absorption and desorption by falling drops through air with low to high concentration of sulfur dioxide. In the liquid phase, a model based on local scales, interfacial liquid friction velocity and drop size diameter is used. In the continuous gas phase a more classical model is applied. Data obtained by the modeling of the SO2 absorption and desorption by a single water drop are compared to published experimental results and a fairly good correspondence was found. On the other hand, the model shows that at high gas concentration (> 1%) the internal resistance to diffusion dominates, while at low gas concentration (< 1000 ppb) the external resistance to diffusion dominates.