The project is a spin-off from MIT's Media Lab: Sharma worked on a device that captures air pollution, as well as the processes needed to strip heavy metals and carcinogens that are also found in exhaust fumes. The Air-Ink magic markers have already benefitted from a successful Kickstarter launch earlier this month. The resulting carbon ink seems virtually indistinguishable from typical black paint and sharpies: the paint / ink is thick and rich, and the Air-Ink pen I got to scribble with felt like, well, any other pen. Thanks to its green origins, users may experience heightened smugness during use.

With some artistic support (and some assistance from Tiger beer: that's its ad above), Graviky hopes to collaborate with governments and transport departments to scale up the scheme, and the tech can be tweaked for use on cars and even commercial (or domestic) chimneys.

The beer brand is also sponsoring a "Clean Air Gallery", that opens this week in Brixton, London, showcasing local artists' works made from the car exhaust ink, while the ad campaign will roll on to Berlin, New York and Singapore in the next few weeks, each with different artists.

Both the ads and artwork shown off to media was made from carbon soot collected locally, as well as from other cities with air quality issues, like Hong Kong, where the scheme was trialled last year. Hong Kong artist Kristopher Ho was responsible for this giant, hand-drawn poster: it's now on a billboard in central London. If fitted across the English capital's fleet of black taxi cabs, it could create 30 trillion litres of cleaner air each year. And just think of all that ink.