Experts have unveiled the latest effort to combat air pollution and spread awareness in London — pigeons with backpacks.

The Pigeon Air Patrol was released yesterday, equipped with tiny backpacks containing instruments that measure air quality and send it back to start-up firm Plume Labs.

The backpacks measure the amount of nitrogen dioxide, ozone and volatile compounds in the air, which is then rated on a scale from "fresh" to "extreme".

Residents are able to tweet to a Twitter account set up for the project, requesting a reading for their location.

The program was launched as part of a marketing program by DigitasLBI, and will run for three days to spread awareness of the air quality in London.

"It is a scandal. It is a health and environmental scandal for humans — and pigeons," designer Pierre Duquesnoy told The Guardian.

"We're making the invisible visible.

"Most of the time when we talk about pollution, people think about Beijing or other places, but there are some days in the year when pollution was higher and more toxic in London than Beijing, that's the reality."

Mr Duquesnoy, who won a London Design Festival award for the idea last year, said he was inspired by carrier pigeons in the first and second world wars, but that they were also a practical way of taking the readings and avoiding congested roads.

"There's something about taking what is seen as a flying rat and reversing that into something quite positive," said Mr Duquesnoy.

The birds include Coco, the "maverick", Julius, the "hipster", and Norbert — the "intellectual".