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
The patrol is, by the admission of the technology and marketing companies that created it, a publicity stunt meant to raise awareness about the city's harmful air. Birds, it should be noted, are also subject to all sorts of nefarious ailments caused by air pollution, including lung damage and low body weight.
"There's something about taking what is seen as a flying rat and reversing that into something quite positive," Pierre Duquesnoy, creative director at marketing agency DigitasLBI and the brains behind the pigeon pollution monitors, told the Guardian.
Plume Labs, the tech firm, gave assurance that a veterinarian was involved in the project to ensure the safety of the pigeons, whose names include Coco, Julius and Norbert.
The London pigeons are not the first birds to don backpacks for an environmental cause. Vultures in Lima, Peru, have been adorned with GPS trackers and GoPro cameras to hunt down illegal garbage dumping sites.