Student researchers at the University of California, Riverside developed an air-cleaning, titanium-dioxide coating for ceramic tiles shown on two tiles (far left). Uncoated tiles are shown to the right and, at top, a commercially available tile with a titanium dioxide coating.

Student researchers at the University of California, Riverside developed an air-cleaning, titanium-dioxide coating for ceramic tiles shown on two tiles (far left). Uncoated tiles are shown to the right and, at top, a commercially available tile with a titanium dioxide coating.

Credit: University of California, Riverside

Titanium dioxide is finding its way into an increasing number of building materials, including concrete and paint, thanks to its ability to reduce smog using only sunlight. Found in ancient Japanese shikkui lime plaster that retains its stark-white appearance by self-cleaning, the naturally occurring substance has most recently been added to ceramic roofing tiles.

Earlier this month, students at the University of California, Riverside's Bourns College of Engineering announced the development of a titanium dioxide coating that they applied to ceramic roofing tiles common among structures in Southern California. The students then tested the prototype tiles in an atmospheric chamber to find that they removed 88 percent to 97 percent of airborne nitrogen oxide, a primary culprit of smog production that is created when certain fuels are burned at high temperatures. The students extrapolated that a coated roof of an average-sized house would eliminate the same amount of smog-inducing nitrogen oxide annually as a car driven 11,000 miles.

The research, titled "Test Protocol for Evaluating Smog Reducing Roof Tiles," won an honorable mention in the second phase of the Environmental Protection Agency's People, Prosperity, and the Planet student design competition.

The choice to focus on the roof as a pollution-reducing surface is a clever one, given the predominance of roof area that is exposed to direct sunlight. However, ceramic tile is not the primary roofing material in the U.S. due to its relatively high cost. The next phase of the research might therefore include a titanium-dioxide treatment for asphalt-impregnated shingles, which are far more prevalent nationwide.

Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.