An Italian concrete producer has developed a surface treatment for concrete that consumes pollutants by super oxidizing them when exposed to light.   They've treated sidewalks, buildings, and roads and seen a dramatic drop in pollutants in the surrounding air.  A side benefit to the increased oxidation is that the concrete essentially is self cleaning.

Read more about it here and if that link is broken then try this one or search around for "TX Active" which is the name of the additive they're putting in the concrete.