Impact of Surfaces on Ozone-Terpene Conversion Rates in Buildings

March 5, 2007 - 4:00pm

Indoor surface reactions of ozone with terpenes and other unsaturated VOCs may be more important than we previously imagined. In this research, we combine modeling and experiment to provide a better-than-order-of-magnitude estimate of the influence of indoor surfaces on overall conversion rates for the reaction of ozone with terpenes and other unsaturated species. This model combines well-understood transport limitations with reasonably-understood surface kinetics and adsorption isotherms to provide conversion rates (1/h) that can be compared with removal rates for ventilation and gas-phase reaction. For non-terpenes, the reaction probability has been shown to be 10 to 1000 times greater on surfaces than in the gas phase (non-terpenes). Incorporating this range, we show that ozone removal rates at surfaces probably approach their transport limits under typical conditions; this is due to rapid surface reactions. These transport limits appear to be approached even for relatively unreactive, volatile, terpenes such as 3-carene. Since walls represent greater geometric surface area than carpet, and transport is limiting, most of the conversion is taking place on walls. The most uncertain factor in this analysis is the enhancement in the reaction probability over gas-phase reaction probabilities. To overcome this uncertainty, we measured the surface reaction probability of 3-carene adsorbed to glass in a plug-flow reactor. We found that the surface enhances the reaction probability by a factor of 10 to 50. Further, the reaction probability decreases with increasing humidity, probably due to competition for surface sites between ozone and water. In conclusion, ozone surface reactions with terpenes, at typical gas-phase levels, may overwhelm any background reactivity of indoor surfaces and may be responsible for a substantial fraction of ozone and terpene removal indoors. For more information about this seminar, please contact: Hugo Destaillats(510) 486-5897

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