Paving slabs 'clear the air'

Prosperous city streets may be "paved with gold" but researchers in the Netherlands have developed a far more environmentally friendly alternative.

A street in the town of Hengelo, in the eastern province of Overijssel, will be paved with stones that can purify the air, according to their creators at the University of Twente.

Researchers in the university's concrete research laboratory said they have developed paving stones with a top layer that contains titanium dioxide.

When exposed to sunlight, it can convert nitrogen oxide from exhaust fumes into small amounts of nitrates. It is then hoped that rainfall will wash the streets clean.

The technology is based on a Japanese invention, but the university developed a way to use smaller quantities of titanium dioxide to achieve the desired effect, significantly cutting the cost of the paving stones.

Professor Jos Brouwers, the scientist heading the project, told edie the team had calculated the level of nitrates likely to be produced, and said it is not expected to reach harmful levels.

"We can make overall computations from how much nitrates is formed on an average rainfall level and it will be well below the health standard requirements, which are in Holland 25 parts per million in water," he said.

The performance of the stones is expected to vary depending on the amount of sunlight, but it is hoped that the trial, which will start at the end of the year, will prove they can work even on cloudy days.

Professor Brouwers said: "You need daylight, and more particularly the UV component of the daylight.

"On sunny days the activity will be higher than on the cloudy days but even on cloudy days the activity per square metre is high enough."

The team will monitor air pollution levels before the stones are in place, and begin taking measurements early next year after the stones are laid, with the first test results expected around summer.

If they prove successful and gain government approval, Professor Brouwers said he hoped they would one day be used in more polluted cities such as Amsterdam, Utrecht and La Hague.

Kate Martin



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