The impact of photocatalytic paint porosity on indoor NOx and HONO levels

Photocatalytic materials are a potentially effective remediation technology for indoor air purification. In this paper, we assess the impact of photocatalytic paint porosity on the indoor levels of nitrogen oxides (NOx) and nitrous acid (HONO). We observed that the porosity of photocatalytic paints plays a paramount role in the NO2 removal. The increase of pigment volume concentration (PVC), i.e. porosity, from PVC 53% to PVC 80% leads to an increase of the geometric NO2 uptake coefficient from (3.3 ± 0.5) × 10-6 to (3.2 ± 0.1) × 10-4. At the same time, a high quantity of HONO formed by NO2 conversion on the photocatalytic paint is emitted into the air. The formation of HONO, which is considered as a harmful compound and a major player in the oxidative capacity of indoor air, is reduced as the paint porosity increases. Based on these results, further optimization should be considered for future commercialization of photocatalytic paints aimed for indoor applications.