by Michael Keller

A couple of weeks ago, we brought you an art and science project in the United Kingdom that produced a pollution-eating billboard. Now we hear word that a team of engineering students at the University of California, Riverside has shown powerful evidence that the compound used in the billboard and similarly treated roof tiles does an admirable job of removing pollutants from the air.

At the heart of both projects is titanium dioxide, a compound widely used as a pigment in paper, plastic, paint and food. When it is exposed to sunlight, it also becomes a catalyst that causes smog-producing nitrogen oxides and volatile organic compounds to break down into environmentally harmless products.

The students coated two sample roof tiles with different amounts of titanium dioxide and put them in an experimental rig meant to mimic outdoor conditions. Nitrogen oxides were fed into the chamber and ultraviolet lights bathed the tiles in a proxy for sunlight.

A gas concentration detector told them the two coated tiles removed 88 percent and 97 percent of nitrogen oxides introduced into the chamber. Since the two tiles removed similarly high numbers of pollutant and one of the tiles was coated with 12 times the amount of titanium dioxide, the student researchers found that the amount of surface area coated in the catalyst was more important than the amount of catalyst that coats each unit of area.

Scaling the results of their research up, the team found that an average-sized residential roof over the course of a year could break down the equivalent amount of nitrogen oxides produced by a car driven 11,000 miles. They also calculated that 21 tons of nitrogen oxides would be eliminated daily for every one million roofs coated with titanium dioxide.

(Mini atmosphere chamber built by the students for the experiments. Courtesy University of California, Riverside.)

Top Image: At left, two tiles coated with the titanium dioxide mixture. At right, uncoated tiles. At top, a commercially available tile with titanium dioxide. Courtesy University of California, Riverside.