We came across two very different stories about passive methods that can produce cleaner air – methods developed centuries apart. First, in a test that may lead to a breakthrough in the reduction of air pollution, the town of Hengelo in the Dutch province of Overijssel is paving one of its roads with concrete brick said to be able to purify air. The town reports that one-half of a road under reconstruction is being paved with the air-purifying brick, while the other half is being paved with brick of the conventional variety. By measuring the air quality on both sides of the road, the town intends to test the efficacy of the new brick. Town and province officials are conducting the test in cooperation with stone producer Struyk Verwo Infra researchers from the University of Twente in The Netherlands, where the brick were developed.

The University of Twente, in turn, credits the concept to the Japanese. Containing a titanium dioxide-based additive, the paving stones – with the help of the sun – reportedly bind nitrogen oxide particles from car exhaust systems and turn them into less harmful nitrates. When rain rinses these nitrates away, “everything is washed clean,” according to a University of Twente public statement reported in local newspapers. That sentiment taken literally is too rosy because it still leaves unanswered an obvious question about what happens to the nitrates. The town intends to finish the road by the end of 2008. The first air measurements will be taken in early 2009, with the first results expected by next summer.

Next, researchers at Queensland University of Technology (Australia) say they have documented a very old-school, solar-powered method for cleaning the air with stained glass windows that are painted with gold. They also argue that medieval glaziers in medieval were the first nanotechnologists who produced colors with gold nanoparticles of different sizes. The QUT team says the windows purify the air when they are lit up by sunlight. Associate Professor Zhu Huai Yong, from QUT’s School of Physical and Chemical Sciences, says tiny particles of gold, energized by the sun, are able to destroy air-borne pollutants like volatile organic chemicals. “For centuries people appreciated only the beautiful works of art, and long life of the colors, but little did they realize that these works of art are also, in modern language, photocatalytic air purifier with nanostructured gold catalyst,” Professor Zhu said. “These VOCs create that ‘new’ smell as they are slowly released from walls and furniture, but they, along with methanol and carbon monoxide, are not good for your health, even in small amounts,” he said. “Gold, when in very small particles, becomes very active under sunlight.

The electromagnetic field of the sunlight can couple with the oscillations of the electrons in the gold particles and creates a resonance. The magnetic field on the surface of the gold nanoparticles can be enhanced by up to hundred times, which breaks apart the pollutant molecules in the air.” He said the use of gold nanoparticles to drive chemical reactions opened up exciting possibilities for scientific research. “This technology is solar-powered, and is very energy efficient, because only the particles of gold heat up,” he said. “In conventional chemical reactions, you heat up everything, which is a waste of energy. Once this technology can be applied to produce specialty chemicals at ambient temperature, it heralds significant changes in the economy and environmental impact of the chemical production.”