A transient kinetic model has been developed for the simultaneous adsorption of SO2−NOx on Na/γ-Al2O3 sorbent, using step response experimental data from a fixed-bed microreactor. The reactor temperature ranges from 367 to 407 K, and the molar SO2/NO ratio from 2 to 8 with and without NO2. SO2 and NO2 readily adsorb on the sorbent surface, producing SO2* and NO2* species. However, NO and O2 only adsorb simultaneously and in the presence of sufficient SO2* on the surface. The proposed mechanism consists of chemisorption steps for SO2 and NO2, whereas NO and O2 are adsorbed simultaneously via an Eley−Rideal step involving a surface species derived from SO2*. The latter is followed by several consecutive steps involving more SO2* species as well as O2, leading to the formation of a complex with a stoichiometry of SO2/O2/NO of 10/5.5/1. The enhanced SO2 sorption capacity in the presence of NO2 is described adequately by considering that the adsorbed NO2* opens a new reaction path for SO2 adsorption. Both the ...