What you can't smell can harm you...

One thing always strikes me when I go for a walk on the hills: the first time you come to a road or see a car after being on the fells, the smell of the exhaust is really strong and unpleasant. Yet in London and most cities we are immersed in this smell 100s of times over. But we don't smell the air as there is no clean air to create the contrast, which is what our olefactory senses are really picking up. In London, what must be a disgusting 'baseline' of traffic smell is just tuned out by our brains. But that deprives us of a health warning signal.

The pollution levels (NOx pictured) are soaring in the summer heat, the big pink blob over London on 18 July - and it has been awful. What would it take for there to be a partial ban on cars in London on high risk days? Could the congestion charge be increased to £20 on a bad day?