This paper investigates a new test method to assess the photocatalytic activity of plasterboards coated with a TiO dispersion under real-world conditions. The degradation of nitrogen oxides NO (NO and NO) is studied and the photocatalytic efficiency under UV illumination is evaluated in a 10-m room after a constant gas injection. Two ultrafine TiO dispersions are used: 0.85% TiO and 5% TiO, and three types of gas are tested: an NO/NO mixture (8/8 mol-ppm), NO (45 mol-ppm) and NO (45 mol-ppm). The test method presented here is midway between laboratory and real-scale procedures and allows better control of the experimental parameters than a real field experiment. Testing a mixture of NO and NO is a way to get closer to real-world conditions as air is polluted by various gases. This study focuses on the degradation of NO and NO under UV illumination when two types of TiO dispersions are used and highlights the difference in behaviour between these two molecules in terms of photocatalytic degradation. The results show that photocatalytic activity does not appear to be efficient to degrade NO molecules. Another mechanism seems to be responsible for the reduction of the concentration of NO, namely adsorption. Encouraging results are obtained with NO molecules, which can be degraded by photocatalysis. The degradation observed is even greater with the more concentrated TiO dispersion.
Indoor air is contaminated by numerous pollutants, which impact human health, comfort and productivity. These pollutants have various indoor sources such as building materials, furniture, combustion appliances or tobacco smoke. However, the pollution also comes from outside. In urban area, nitrogen oxides (NO x ) emitted into the atmosphere can reach alarming levels. These traffic-related pollutants, which seriously impact the global environment and human health, can infiltrate inside buildings. Therefore, limiting the amount of breathable NO x in outdoor and indoor environments is an important priority for the modern society. The photocatalytic process has attracted particular attention in the last two decades and has proved to be efficient to reduce the concentration of NO x . However, further work has to be conducted to assess its efficiency in real indoor environments. The purpose of this paper was to report on the indoor air quality in an open space office in Manchester, UK. Focus was made on nitric oxide (NO) and nitrogen dioxide (NO 2 ). The indoor concentrations of both gases were monitored from 14 January 2019 to 7 April 2019. During this period, a photocatalytic coating was applied to a part of the indoor wall. The influence of this coating on the level of NO x was assessed by comparing the indoor concentrations before and after the application. An attention was paid to the correlation between outdoor and indoor pollution and to the effect of other parameters such as temperature, humidity, pressure and ozone (O 3 ) concentration. The results showed that the photocatalytic process led to a decrease in the NO x concentration. The likelihood to find concentrations above 35 ppb for NO and 7.5 ppb for NO 2 was clearly reduced after the coating application.
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