Sept. 18, 2006 issue - The Italian cities of Cagliari, Sassari and Selargius plan this month to begin laying a new sidewalk brick that eats smog. The bricks are made with a titanium-dioxide blend that, when exposed to light, turns carbon monoxide (smog) in the air into water and carbon dioxide—the gas in soda pop. Rossano Amadelli, who led tests for the Italian National Research Council, says he was "stunned" by how well the tiles work. Cost: $24 a square meter, 46 percent more than conventional bricks.
46% more than normal brick is a lot, and I betcha that's a whole lot more than standard pour-and-let-dry cement like we have in most cities in the US, but if the sidewalks can bond with carbon monoxide and turn it into CO2, this might just be worth the expense. Awesome.