The London Air Quality Network at King's College London offers a "nowcast" on its website of pollution levels across the city, updated by the hour using reports from air monitoring stations across the area. The real-time (or almost real-time) visualization is impressively specific, allowing any Londoner to zoom into a view of Ozone, Nitrogen Dioxide and particle pollution levels practically down to the block.
What's more telling about these maps though, whether you live in London or not, is the way they they visually highlight the predominant source of the problem: "Much of the pollution in London," the researchers write, "is associated with traffic."
This map, taken as of 5 p.m. London time today, shows particle pollution in the city, with elevated levels in darker blue:
This is a map of Nitrogen Dioxide:
And this one, zoomed in further, shows Ozone levels:
We're essentially looking at the city's street network, with the busiest roads also doubling as the worst sources of pollution. And that pattern would appear the same in cities everywhere. All of the pollution levels currently shown are considered low and unlikely to cause health effects. But these pictures give a good indication of where we might want to target efforts to reduce pollution even further.