New Scientist reports that a pollution-catalyzing paint will be available next month in Europe. Ecopaint claims to be able to soak up specific gases from vehicle exhausts, just as trees do with CO2 emissions. Though I'll point out that we don't know how much equivalent pollution is generated by its manufacture, this would appear to be a great band-aid while we argue about how to avoid producing NOx at all.
"...the substance is designed to reduce levels of the nitrogen oxides, collectively known as the NOx gases, which cause respiratory problems and trigger smog production."
"The polysiloxane base is porous enough to allow NOx to diffuse though it and adhere to the titanium dioxide particles. The particles absorb ultraviolet radiation in sunlight and use this energy to convert NOx to nitric acid... The acid is then either washed away in rain, or neutralised by the alkaline calcium carbonate particles, producing harmless quantities of carbon dioxide, water and calcium nitrate, which will also wash away."
The paint's also environmentally responsive, letting you know that it's reached capacity:
"In a typical 0.3-millimetre layer, there will be enough calcium carbonate to last five years in a heavily polluted city, says Robert McIntyre of the British company Millennium Chemicals, based in Grimsby, Lincolnshire, which developed the paint. When the carbonate has been exhausted, the titanium dioxide will continue to break down NOx, but the acid this produces will discolour the paint.
"In 2002, after 7000 square metres of road surface in Milan, Italy, were covered with a catalytic cement, residents reported that it was noticeably easier to breathe - with the concentration of nitrogen oxides at street level cut by up to 60 per cent.