Africa’s skies are badly polluted

GORéE ISLANDWHO, a former slave-trading hub, is so close to Dakar, Senegal’s capital, that hundreds of amateurs swim out to it every year. Yet some days it disappears from sight, lost in a haze of pollution and dust. In the Nigerian city of Port Harcourt, part of its oil-producing region, black soot settles on everything. Tiny particles clog lungs and invade the bloodstream.Some 4.2m people die prematurely every year from dirty outdoor air, says the World Health Organisation (). The World Bank reckons the worldwide costs of deaths from air pollution run to $5trn a year. Africa is plainly affected, but it is hard to know how badly. Outdoor pollution in the continent is rarely measured.