Air pollution caused by diesel vehicles in London is bad - so bad that it is blamed for 9500 premature deaths a year and has prompted Britain's Supreme Court to order the Government to make a plan for cleaning up the skies.
Now what is commonly seen as another scourge of the city, the pigeon, is helping in the fight against smog.
On Monday, 10 birds outfitted in miniature backpacks carrying pollution sensors and GPS trackers took to the air, and they started tweeting - via beak, perhaps, but definitely via Twitter - their devices' readings of nitrogen dioxide and ozone.
Londoners who tweet at the Pigeon Air Patrol's Twitter handle, @PigeonAir, are getting responses from the birds about air pollution in their area, and a live map of the pigeons' locations can be viewed online.
There's something about taking what is seen as a flying rat and reversing that into something quite positive