About the Seminar: Indoor chemical exposures frequently match or exceed those experienced outdoors. The large fraction of time most people spend indoors makes this true even for species with greater outdoor abundances, such as ozone. Ozone is a criteria air pollutant with harmful respiratory and cardiovascular effects. Transport of polluted outdoor air brings ozone indoors, where it rapidly oxidizes abundant unsaturated organic molecules. Such chemistry attenuates concentrations relative to outdoors, but simultaneously produces toxic and irritating chemical species. The health effects of indoor ozone therefore depend both on ozone itself and its reactive fate. However, the complexity of the indoor environment makes characterizing ozone reactivity and fate challenging. The existence of multiple sources for a single chemical makes attributing compounds to ozone chemistry exceedingly difficult. Lab studies have identified numerous products of ozone chemistry, but extrapolation requires caution. Additionally, while chemical and physical characteristics of an environment are expected to control ozone reactivity, their influences remain unclear. By adding stable isotope labeled ozone to a well-controlled, realistic indoor space, it is possible to reduce uncertainty in the fate of indoor ozone. Observing how ozone behavior and fate changes in response to chemical and physical perturbations can also provide insight into drivers of ozone reactivity.