It could hardly be simpler. Whilst other major cities around the world grapple with the question of how to deal with tighter restrictions on acceptable air pollution, Madrid has shown the way forward. Forget all those schemes that try to reduce traffic, all you need to do is move the machines that measure contaminants from those areas that have high pollution figures to others that have lower ones.
This, it seems, is how Madrid has managed to achieve an impressive reduction in nitrogen dioxide levels in just 12 months. Nicely timed to coincide with tighter European legislation. This is a change from the previous, slightly cruder strategy, of claiming that the machines taking the readings were broken whenever there was an extended spell of calm sunny weather. So there you have it. If you find that you are having problems breathing at any time in Madrid it's because you have chosen to live in the wrong area. It could become a new selling point - living near one of the city's air quality measuring machines.