NITROGEN OXIDES are nasty things. Among the gases generated by power plants and car exhaust, they react with other compounds in the air to create smog. But researchers at Eindhoven University of Technology in the Netherlands came up with a novel idea. They coated paving stones with another substance, titanium oxide, which tends to neutralize NOx. Then they paved a city block in the Dutch town of Hengelo with their smog-sucking creation. According to a paper published in the Journal of Hazardous Materials, their tests over the course of a year showed that nitrogen-oxide levels could drop as much as 45 percent on a good day compared with another block nearby that didn’t have the special pavement. There will certainly have to be more tests, and then mass production to make the pavement economically viable. And it’s far from clear that the big cities in Europe, the Americas, and Asia that really need this kind of help will actually find the political will to pay for it. But when the Los Angeles Times ran a small article on the “smog-eating streets” and asked readers whether they thought the technology would eventually be used in L.A., there wasn’t much doubt: 69 percent said yes.