An accelerated weathering apparatus of the type used to concentrate solar radiation upon test specimens includes a frame supporting a reflecting solar concentrator disposed in opposition to a target board. A channel is connected to the target board and includes a cover to define a chamber. A fluid source is in communication with the chamber, whereby a fluid introduced into the chamber reacts with the test specimens in order to accelerate degradation of the test specimens during exposure to concentrated solar radiation. Cooling apparatus contiguous with the test specimens may also be included.