Reuters: An effort by the World Health Organization to measure pollution in cities around the world has found New Delhi admits to having the dirtiest air, while Beijing's measurements, like its skies, are far from clear. The study of 1,600 cities found air pollution had worsened since a smaller survey in 2011, especially in poorer countries, putting city-dwellers at higher risk of cancer, stroke and heart disease. Air pollution killed about 7 million people in 2012, making it the world's single biggest...