Cement mixed with an agent called a photo-catalyzer (titanium dioxide) speeds up the natural process that breaks down smog into its component parts. The smog-eating cement is called TX Active, and the Italian firm Italcementi spent 10 years developing it. Now there's a busy street in Segrate that's covered with it, and Italcementi claims it has reduced nitric oxides in the area by as much as 60%.
Bonus: buildings made with TX Active stay cleaner too.
View information on another project where TX Active has been used in Chicago.
View information on photocatalytic concrete used at Dalton College Tower, in Georgia, USA.