Ozone Deposition in Ventilation Ducts
In the same Morrison et al. study, the rate of ozone uptake on HVAC system materials was measured to predict how much ozone might be removed by a typical duct system. For exposure to a constant ozone concentration of 37 ppb, the modeled duct system would be expected to remove about 9% of the ozone initially. However, over a period of 10 days of constant exposure, the ozone removal efficiency would diminish to less than 4%. In an equivalent unlined duct system, in which only galvanized sheet metal was exposed to air, the removal efficiency would be much lower at approximately 0.02%. Thus, ducts in ventilation systems are unlikely to be a major sink for ozone. The implication is that duct surfaces probably do not greatly reduce the concentrations of ozone entering buildings through HVAC systems.

Ozone, Carpets and VOCs: First Investigation
Indoor ozone concentrations can be a significant fraction of outdoor ozone concentrations. In locations with severe photochemical smog, indoor ozone often exceeds 50 ppb. Ozone is a powerful oxidizing agent. In the gas phase, it reacts with VOCs that contain unsaturated carbon-carbon bonds such as terpene hydrocarbons to produce oxidized species. Ozone also reacts with relatively nonvolatile compounds on interior surfaces to generate oxidation products that are volatile. The first study of the effect of ozone oxidation on indoor air quality was conducted in the IED in the early 1990's (Weschler et al., 1992). In that study, VOCs were measured in a freshly carpeted, ventilated 20-m³ stainless steel chamber in both the absence and presence of ozone at 30 to 50 ppb. Four different new carpets were studied. The gas-phase concentrations of unsaturated hydrocarbons emitted by the carpets (e.g., 4-phenylcyclohexene, 4-vinylcyclohexene and styrene) significantly decreased in the presence of ozone. Conversely, the concentrations of formaldehyde, acetaldehyde and C5 to C10 aldehydes significantly increased. The concentrations of total VOCs also increased in the presence of ozone. The additional VOCs appeared to have been generated by the reaction of ozone with relatively nonvolatile compounds associated with the carpets. This work subsequently lead to more detailed investigations of ozone uptake and interactions with carpet.