The Wall of Silent Falls - The Purifying Power of Light Falling on Funabashi - March 2001

The Wall of Silent Falls - The Purifying Power of Light Falling on Funabashi - March 2001

An air purification experiment using photocatalytic paint containing titanium dioxide (TiO₂) conducted in Funabashi, Chiba Prefecture, from 2000 to 2001 attracted nationwide attention as a new environmental measure in urban areas. Photocatalytic reactions occur when sunlight shines on the painted building walls, oxidizing and decomposing nitrogen oxides (NOx) in the air.

In this experiment, 50 square meters of building walls in Funabashi City were painted, and the effect of removing 2.57 grams of NOx per square meter was confirmed after one year of observation. In terms of conversion, this means that the amount of NOx emitted by 1,600 gasoline-powered vehicles traveling 1 km can be treated, demonstrating the effectiveness of the system as an air purification measure in urban areas.

What is unusual about this initiative is that it was a municipal government initiative to actually visualize and quantitatively evaluate the air purification effect of photocatalysts on urban walls. The technology, which until then had been limited to theory and experimentation in the laboratory, began to function with the light falling on the walls of the city. It was as if a silent waterfall was washing away the shadows of exhaust gases.

Furthermore, the fact that the amount of NOx removal was explained in terms of "automobile emissions" was excellent as an easy-to-understand environmental awareness campaign for the public, and an attempt to shorten the distance between science and society.

This "light waterfall" quietly but surely shows its effect on the invisible pollution that is poisoning the city. If applied to public facilities and urban spaces in the future, this technology could open up a new vision of cities where the environment and landscape are in harmony.

Related Information
The detailed results of this experiment are described in a document published by the Resource Recycling Promotion Division of Chiba Prefecture, which reports in detail on the area of the experiment, the amount of NOx removed, the evaluation method, and future technical prospects.