The search for solutions to the threat of polluted air is generating ideas that range from the modest to the radical to the bizarre.
A London primary school may issue face-masks to its pupils. The council in Cornwall may take the extreme step of moving people out of houses beside the busiest roads.
Four major cities – Paris, Athens, Mexico City and Madrid – plan to ban all diesels by 2025. Stuttgart, in Germany, has already decided to block all but the most modern diesels on polluted days. In India’s capital, Delhi, often choked with dangerous air, a jet engine may be deployed in an experimental and desperate attempt to create an updraft to disperse dirty air.
The World Health Organization calculates that as many as 92% of the world’s population are exposed to dirty air – but that disguises the fact that many different forms of pollution are involved.
For the rural poor, it is fumes from cooking on wood or dung indoors.
For shanty-dwellers in booming mega-cities, it is a combination of traffic exhaust, soot and construction dust.
In developed countries, it can be a mix of exhaust gas from vehicles and ammonia carried on the wind from the spraying of industrial-scale farms.
In European cities, where people have been encouraged to buy fuel-efficient diesels to help reduce carbon emissions, the hazard is from the harmful gas nitrogen dioxide and tiny specks of pollution known as particulates.
The first step is to understand exactly where the air is polluted and precisely how individuals are affected – and the results can be extremely revealing.