When supply air passes through a filter, ozone and other oxidants may react with the dust and with the compounds adsorbed on it causing decomposition of ozone and producing oxidation products. These reactions have been studied on nine used supply air filters in the laboratory. Some consumption of ozone was observed in almost all the filters. The changes in the concentrations of individual organic compounds due to penetration through the filter were negligible, except for formaldehyde which was produced. Air velocity in the range of 0.1-0.2 ms−1 and ozone concentration from 20 to 60 ppb did not have an effect on reduction. In field experiments, the reduction in ozone concentrations varied from 8 to 26%; the highest reduction was obtained in a HVAC unit with a three-stage-filtration. Sensory evaluation demonstrated that the highest odour emission was caused by the pre-filter. At elevated ozone concentration, the panelists could not detect any odour differences before and after the filters. Expectedly, the reactions did not change the VOC concentrations appreciably, but the reaction products with low odour threshold concentrations may, nevertheless, have some influence on the odour perception.
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