The report presents results of factors affecting environmental chambers used to study photochemical reactions in the lower atmosphere. Described are the facilities, the chamber, the light source, and some photochemical reactions. The work has shown the practicality of operating an environmental chamber externally illuminated by a collimated beam of light from an xenon arc lamp. It has also demonstrated that a vacuum chamber pumpdown of the environmental chamber is a feasible method of chamber cleaning. Analytical chemistry methodology has been demonstrated for the photochemical reaction products of interest.