Guardian: During these cold winter days, Anumita Choudhury dare not leave her small second-floor apartment in Delhis northern suburbs. Elderly now, she has developed asthma. The last time she ventured into the streets of the worlds second most populous city she began gasping for breath and had to be helped home by her neighbours.
The story is the same in many of the worlds great cities. From Kabul in Afghanistan to Hong Kong and Shijiazhuang in China, and from Lima to So Paulo in Latin America, people...