In situ NO abatement by photocatalysis—study under continuous NO injection in a 10-m3 experimental chamber

Air pollution is a serious public health concern in France and many other countries. Nitrogen oxides (NOx) include nitrogen monoxide (NO) and nitrogen dioxide (NO2). They are mainly outdoor pollutants produced during combustion of fossil fuel. These gases can easily infiltrate buildings and thus increase indoor pollution. The recommended guideline values for NO2 are 200 μg/m3 (short-term exposure) and 40 μg/m3 (long-term exposure). Although no guideline values exist for NO, this gas can be oxidised by atmospheric ozone and thus produce NO2. This paper studies the depollution efficiency of photocatalysis towards indoor NO. Experiments were conducted at real scale, in a 10-m3 experimental chamber developed at the LMDC and used as a reactor. The interior walls of the chamber were equipped with painted plasterboards treated with photocatalytic coating (3 g/m2 of TiO2). Gas was continuously injected into the chamber according to a specific procedure: (1) pollutant injection at high flow rate to reach 200 ppb of NO, (2) pollutant injection at low flow rate in order to keep the NO concentration constant at 200 ± 10 ppb and (3) photocatalysis activation by switching on the light. Typical indoor lighting systems (fluorescent tubes, LED and halogen bulbs) were tested and UV fluorescent tubes were also used to optimise the photocatalytic efficiency. Results showed that NO indoor concentration was reduced by photocatalysis in real-world conditions. Significant NO degradation was obtained under visible light. In addition, using the experimental procedure presented in this paper, a new method for evaluating air depollution efficiency by photocatalysis at real scale is proposed.