If your house were infested with mosquitos, you might put up flypaper strips to trap them. London mayor Boris Johnson is taking roughly the same approach to air pollution — he's having street sweepers spray a calcium-based adhesive onto the ground to trap particulate air pollution. It sounds like a stupid idea, and maybe it is. But it also seems to work.

The pollution glue traps have reduced particulate levels by 14 percent in the air pollution hotspots that are being targeted. Of course, one of those hotspots is the official air monitoring station, whose data will be used to determine whether London is in violation of E.U. pollution standards. But surely that's just a coincidence!

This program is massively expensive ($1.4 million so far), but not as expensive as the fines London would have to pay if it got in trouble with the European Commission, which enforces pollution standards. So opponents criticize it both for being a waste of money and for being a transparent attempt to do an end-run around environmental regs. But to be fair, it's not London's only plan for mitigating air pollution. According to the chief operating officer of Transport for London, the city will also be instituting cleaner buses, getting rid of the most polluting taxis, tightening emissions standards, planting trees, and "innovative dust suppressant technology."

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