Despite concerning air pollution in multiple cities and countries around the world, such as London and multiple regions in China, India, and Thailand, Marley Eternit's motives are not completely altruistic here, as the company surely stands to benefit should such policies come to fruition. We are also skeptical that photocatalytic coatings can improve air quality in outdoor applications like building exterior walls and roads for several reasons.
First, the volume of outdoor air pollutants overwhelms the active materials in photocatalytic coatings, so the actual air purification effect is limited. For example, air pollutants can spread from a height of several tens of meters to the ground and occupy hundreds or thousands of cubic meters, while the active coating materials are only applied in square meters. Theoretically, each square meter of coating will need to combat air pollutants spread out over multiple cubic meters above the coating surface. Consequently, achieving significantly improved air quality for occupants or pedestrians is quite the challenge.
Second, the cited study is based on "ideal weather conditions," which are not applicable to other outdoor applications. Optimum air purification performance of photocatalytic coatings relies on exposure to UV and very slow wind speed that are not typically available simultaneously, in most actual environments.
We believe the government should provide photocatalytic coating subsidies for indoor use, such as walls, floors, and ceilings. Compared with outdoor conditions, the indoor environment is much more "sealed," with smaller and more manageable volumes of air pollutants relative to the active coating materials. Also, indoor environments have access to UV and nearly zero wind speed. Leading suppliers of photocatalytic coatings, like PURETi and SunWash, already target indoor applications, such as those in functional buildings (like hospitals) and cities with significant air pollution. Readers should closely follow the progress of these suppliers in indoor applications, since air pollution in multiple parts of the world generates business opportunities with immediate market demand and high requirements on air purification performance.
Jerrold Wang is a Research Associate for the Sustainable Building Materials Intelligence service at Lux Research, which provides strategic advice and on-going intelligence for emerging technologies.