Films of the base polymer used in a latex paint have been exposed to various combinations of UV/SO2/H2O/air. The polymer is primarily a terpolymer of butyl acrylate, vinyl acetate, and vinyl chloride. Reported here are results from dynamic mechanical analysis (Tg), sol-gel analysis, intrinsic viscosity and contact angle measurements. Exposure without the presence of UV and causes virtually no change in the properties of the films. In the presence of UV and clean air containing O2. there is evidence of both chain scission and crosslinking. When films are exposed to combinations of either UV/SO2 or UV/SO2H2O, a dramatic increase in the rate of change in the properties is observed, indicating a synergistic interaction between UV and SO2. The gel fraction increases from about 20% for the control to about 65% in samples exposed to UV/SO2 or UV/SO2/H2O for as little as 24 h. In the latter exposed samples, there is a corresponding precipitous drop in the intrinsic viscosity of the soluble fraction, a significant increase in the surface polarity of the films, and a large increase in the Tg. Reaction mechanisms for changes resulting from the various exposure conditions are proposed.