One of the most significant applications of photocatalytic coatings is in air purification. When applied as very thin films on building facades, roofing tiles, interior surfaces like walls and ceilings, these coatings can remove air pollutants through photocatalytic oxidation. As nanoparticles of TiO2 are dispersed through the coating, sunlight activates them to continuously clean the air by breaking down smog, odors and other volatile organic compounds. Several field studies have demonstrated up to a 40% reduction in ambient NOx levels around buildings coated with these materials. They also help eliminate indoor air pollutants and allergens to create healthy indoor environments.