Besides the air itself, the road surface on which we drive is typically the closest thing, physically speaking, to tailpipe emissions, which led researchers from the Netherlands' Eindhoven University of Technology to resurface 1,000 square meters of busy road with special air-purifying concrete paving stones. Another section was paved with regular stones. According to Gizmag:
"The air-purifying concrete contains titanium dioxide, a photocatalytic material that removes the nitrogen oxides from the air and converts them into harmless nitrate with the aid of sunlight. The nitrate is then rinsed away by rain."

The results so far have been promising: After their first measurements, the section with titanium dioxide was found, from a height of one-half to one-and-a-half meters, to have a nitrogen oxide (NOx) content a full quarter to 45 percent less than that of the untreated area. More tests are forthcoming later this year.

I like this way of thinking, which uses the existing infrastructure to cut down on harmful emissions. Perhaps we can coat the interior of the cars driven by those idiots, who insist on blasting their music a full volume, with some sort of sound-deadening material?