Material chemistry and surface reactivity during cyclic ozone exposures
Ozone is a naturally occurring atmospheric gas with the ability to enter and be generated indoors. The indoor environment accounts for 25-60% of ozone inhalation. Lung function can be affected when people are exposed to ozone. In addition, when ozone enters the indoor environment it reacts with material surfaces and can affect the product life and function of these materials. Materials can also be chosen for the ability to remove ozone. This study focused first on ozone aging of material surfaces. Clay paint and ceiling tile were observed to be more reactive with ozone compared to particleboard and latex paint. The material ranking in order of highest to lowest reactivity were ceiling tile, clay paint, latex paint, and particleboard. These materials were exposed to air with and without ozone, with the goal to study the effect of diurnal oscillation of ozone in an indoor environment. Indoor ozone concentration oscillation can be driven either by variation in outdoor ozone concentration or by intermittent operation of the ventilation systems that bring outdoor ozone into the indoor environment. Over prolonged exposure to ozone the surface reactivity decreases, while a period without ozone exposure often allows “regeneration” of material reactivity. Laboratory experiments showed that after 18 hours of no ozone exposure, clay paint, ceiling tile, particleboard, and latex paint exhibited some regeneration. Materials with the lowest reactivity, latex paint and particleboard, showed the largest percent decrease in reactivity during ozone exposure, and the most samples with regeneration. Follow-up experiments, involving field aging of clay and latex-painted surfaces (without surface deposition), shows that ozone-driven surface reactivity decreases over a two year period. However, placement of samples for three months in a residential kitchen (with surface deposition) leads to increased ozone reactivity, lasting multiple exposures. When the clay paint and latex paint were exposed to ozone the gas-phase compound profile between the paints differed. Indicating that secondary emissions exposures would differ based on the specific paint. The paints were found to not only differ in ozone removal and byproducts, but also in the estimated toxicity of the byproducts. The gas-phase results help provide understanding to the decomposition of dried paints, degree of unsaturation during ozonolysis, and the original ingredients. This dissertation highlights the diversity of indoor material behavior during ozone-driven chemistry for four common indoor materials.