A gas turbine system includes an exhaust processing system that may process exhaust gas generated by a gas turbine engine, the exhaust processing system includes an exhaust diffuser that may receive the exhaust gas from a turbine of the gas turbine engine and having an annular passage disposed between an inner annular wall and an outer annular wall, and an air injection assembly disposed within the exhaust diffuser. The air injection assembly includes one or more air injection conduits disposed within the annular passage of the exhaust diffuser and including fluid injection holes that may direct a cooling fluid into a first mixing region of the exhaust diffuser.