A new paint set to go on sale in Europe in March promises to absorb the most noxious gases from automobile exhaust. Invented by British company Millennium Chemicals, Ecopaint contains spherical nanoparticles of titanium dioxide and calcium carbonate, suspended in a base of polysiloxane (a silicon-based polymer). Hey, wake up, the good part is coming! The base is sufficiently porous to allow nitrogen oxides to permeate it and attach to the nanoparticles, which convert the NOx to relatively harmless nitric acid. The paint is expected to last five years in a heavily polluted city before becoming discolored. The nonoparticles are so small — so darn nano — that the paint is clear, which means it can be dyed any color. The first color sold will be white. We look forward to green.