An adjustable airflow diffuser for selectively diffusing a flow of treatment gas includes a first member adapted to be disposed in the flow and a second member movably coupled to the first member and also adapted to be disposed in the flow. The second member is selectively moveable from: (i) a first position with respect to the first member in which the first member and the second member form a first turbulating arrangement, and (ii) a second position with respect to the first member in which the first member and the second member form a second turbulating arrangement.
