Photooxidizing films of poly(vinyl butyral) were investigated for the generation of solid-state and volatile peroxide species, acids, and changes in mass in order to gain insight into the factors that influence the levels of these peroxides during oxidation. Both the concentration of solid-state peroxides and the emission rate of volatile peroxides increased and subsequently declined, while acidic groups in the polymer accumulated without decreasing. After an initial increase, the mass of the films fell as volatile degradation products were released. It is suggested that the decline in the peroxide species, both in the polymer and volatiles, may be due to their reactions with other products of the polymer's oxidation, including aldehydes and acids. These results indicate that reactions besides the often-invoked homolytic cleavage of hydroperoxides may remove these species from the poly(vinyl butyral) and similar materials during advanced stages of photooxidation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39753.