Fresh (air) Paint

Smog-busting paint soaks up noxious gases

This article in New Scientist discusses a paint that uses titanium dioxide and calcium carbonate to bind Nitrogen Oxide gasses which are pretty much toxic. The gas molecules bind to the paint partices, oxidize and then slough off in water.
This type of catalytic surface has been used in numerous test around the world. One such test in Milan Italy showed that 7000 square metres of road sufrace reduced nitrogen oxides by about 60%.
The paint base itself is clear, so it could come in any color you like.