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Imagine using a common, inexpensive chemical to rid urban air of smog. Researchers at the University of California at Riverside (UCR) did just that and came up with a coating for tile roofs that does the job.

The students at the university's Bourns College of Engineering report that coating an average-size residential tile roof coated with titanium oxide can break down the smog generated by a car with an internal-combustion engine driven for 11,000 miles.

The high heat of engines in conventional cars emit, among other things, nitrogen oxides, which react with airborne organic gases and, with the help of sunlight, create smog, such as the pall that blights the landscape of much of Southern California, where houses with tiled roofs abound.

Titanium oxide, meanwhile, is ubiquitous, found in everything from cosmetics to foods, and because it's plentiful, it's inexpensive. The UCR team used titanium oxide to coat common roof tiles and placed them in a small, makeshift atmospheric chamber fitted with a gauge that measures atmospheric concentrations of nitrogen oxides.

Finally, they bathed the interior of the chamber with ultraviolet light, simulating sunlight. The titanium oxide eliminated between 88 percent and 97 percent of the nearby nitrogen oxides. And the experiment worked regardless of how heavily the roof tiles were coated. What's important is the surface area of the coated tile, not depth of the coating.

Perhaps the best news is how inexpensive the titanium coating is. The UCR students say the number of tiles needed to cover an average home can be coated for about $5 during manufacturing. Presumably, though, the cost would be higher to apply the coating to existing roofs.

And because the area of the coating is the most important factor in ridding the air of smog, the students hope to add titanium oxide to exterior paint for houses, as well using it to coat concrete and even dividers along highways.

Yet to be answered is how long a coating will last, and whether titanium oxide coating, which is white, will work as well in another color.


Written by Andy Tully at