Funabashi City Experiment: NOx Absorption by Paint? Potential of Photocatalytic Paints (2001)

Funabashi City Experiment: NOx Absorption by Paint? Potential of Photocatalytic Paints (2001)

In 2001, air pollution caused by automobile exhaust gas was one of the most serious urban environmental problems in Japan. In particular, pollutants such as nitrogen oxides (NOx) and suspended particulate matter (SPM) were attracting attention as causes of health problems such as asthma and bronchitis, and the government was tightening air quality standards. Under these circumstances, the Ministry of the Environment initiated the "Eco-Town Project" and local governments began to introduce their own technologies in various areas, and the demonstration experiment of photocatalytic paint conducted by Funabashi City, Chiba Prefecture, is a pioneering example.

Funabashi City has introduced a new technology on the walls of public facilities on a trial basis, in which paint containing titanium dioxide (TiO₂) is applied to the walls to oxidize and decompose NOx through a photocatalytic reaction triggered by ultraviolet rays of sunlight. As a result, an annual NOx removal effect of 2.57 grams per square meter of paint was confirmed. This figure may seem small at first glance, but when converted to a 50-square-meter wall surface, it leads to the shocking estimate that it can absorb the NOx emitted by 1,600 gasoline-powered vehicles driving one kilometer.

Behind this is the rapid progress in photocatalytic research since the late 1990s, when a Japanese manufacturer became the first in the world to commercialize photocatalytic technology in 1996, which has attracted attention for its many uses, including self-cleaning and antimicrobial activity.

Another reason the city's experiment attracted attention was an evaluation of the feasibility of introducing the technology on an urban scale. Conventional air purification measures have mainly relied on vehicle regulations and filtering technology, but the idea of improving air quality simply by "painting" buildings is an attempt to redefine the urban space itself as an "environmental device.

This approach is connected to the green building materials and zero-emission building (ZEB) concepts of the 2000s. It also attracted attention as a model case of a municipality-led social experiment in environmental technology, in which the local government collaborated with private-sector technology, and it spread to other cities.

Although photocatalytic technology does not solve all air pollution, it was a good example of a new "passive" environmental measure that utilized everyday urban space, standing at the intersection of urban policy and technological innovation at the time of 2001.