Air pollution is one of the world’s biggest killers, accounting for one in ten deaths each year – 6.5 million people – according to the World Health Organization. That is six times more than are killed by malaria, and four times more than HIV/Aids. About half of these deaths are due to outdoor pollution in towns and cities. Poor air quality increases the risk of stroke, heart disease, lung cancer and chronic and acute respiratory diseases, including asthma. As well as the terrible toll on health, the World Bank reckons that it costs the global economy around $225 billion a year in lost labour income.
More than 80 per cent of people living in urban areas are now exposed to air quality levels that exceed safe limits – and since 2010, more than half of the world’s population has lived in cities. It is in the developing world that the situation is most severe: almost all cities in poor countries fail to meet guidelines.