Gas-Phase Advanced Oxidation for Effective, Efficient in Situ Control of Pollution

In this article, gas-phase advanced oxidation, a new method for pollution control building on the photo-oxidation and particle formation chemistry occurring in the atmosphere, is introduced and characterized. The process uses ozone and UV-C light to produce in situ radicals to oxidize pollution, generating particles that are removed by a filter; ozone is removed using a MnO₂ honeycomb catalyst. This combination of in situ processes removes a wide range of pollutants with a comparatively low specific energy input. Two proof-of-concept devices were built to test and optimize the process. The laboratory prototype was built of standard ventilation duct and could treat up to 850 m³/h. A portable continuous-flow prototype built in an aluminum flight case was able to treat 46 m³/h. Removal efficiencies of >95% were observed for propane, cyclohexane, benzene, isoprene, aerosol particle mass, and ozone for concentrations in the range of 0.4–6 ppm and exposure times up to 0.5 min. The laboratory prototype generated a OH^• concentration derived from propane reaction of (2.5 ± 0.3) × 10¹⁰ cm^–3 at a specific energy input of 3 kJ/m³, and the portable device generated (4.6 ± 0.4) × 10⁹ cm^–3 at 10 kJ/m³. Based on these results, in situ gas-phase advanced oxidation is a viable control strategy for most volatile organic compounds, specifically those with a OH^• reaction rate higher than ca. 5 × 10^–13 cm³/s. Gas-phase advanced oxidation is able to remove compounds that react with OH and to control ozone and total particulate mass. Secondary pollution including formaldehyde and ultrafine particles might be generated, depending on the composition of the primary pollution