Titanium dioxide is also used on the inside surfaces of windows, for the same purpose. I don't know how widespread its use is, though. http://en.wikipedia.org/

Titanium dioxide is also used on the inside surfaces of windows, for the same purpose. I don't know how widespread its use is, though. http://en.wikipedia.org/wiki/Titanium_dioxide#As_a_photocatalyst http://en.wikipedia.org/wiki/Titanium_dioxide#As_a_photocata...