The adsorption study Of SO2 onto the activated carbon prepared from pistachio-nut shell was studied theoretically and experimentally. A single-particle sorption model known as concentration-dependent surface diffusivity micropore, surface and macropore diffusion control model incorporating micropore, macropore and surface diffusions, together with a nonlinear isotherm at the micropore mouth, has been derived and solved by a finite difference method. The effects of different types of nonlinear isotherms and concentration dependent surface diffusivities have been thoroughly studied. The effects of adsorbate concentration and temperature on adsorption were studied experimentally. Good agreement was found between the model predictions and the experimental results. The value of the tortuosity factor and the extracted diffusion coefficients obtained are consistent with their corresponding values reported. (c) 2008 American Institute of Chemical Engineers AIChE J, 55: 423-433, 2009