Google's Street View cars are well suited to the job, and their inherent roaming nature has been used to the advantage of similar projects in the past. In 2015, sensor-equipped cars began recording air composition in California, and last year Google published data it captured in the Oakland area and subsequently, several broader regions. Google Earth Outreach joins many other parties working on this new London initiative, including King's College London, the University of Cambridge, the National Physical Laboratory and Environmental Defense Fund teams in Europe and the US.

Sadiq Khan has been particularly bullish about improving the quality of London's air during his tenure, and numerous small gains are happening across the capital all the time. Recently, he announced another 70-odd zero-emission buses would be joining the existing fleet next summer, as well as plans to expand London's ultra-low emission zone in which the most polluting vehicles must pay a daily charge to enter. With many green initiatives in progress, though, it's important to be able to document their impact. That's where this hyperlocal monitoring project comes in -- by creating a detailed map of air quality across the city, you then have a baseline to compare future readings against.