Beijing

NASA/Goddard Space Flight Center
A satellite image shows a dense blanket of polluted air over central eastern China covering the coastline around Shanghai. The "Asian Brown Cloud" is a toxic mix of ash, acids and airborne particles from car and factory emissions, as well as from low-tech polluters like wood-burning stoves.
NYTimes:

A noxious cocktail of soot, smog and toxic chemicals is blotting out the sun, fouling the lungs of millions of people and altering weather patterns in large parts of Asia, according to a report released Thursday by the United Nations.

The byproduct of automobiles, slash-and-burn agriculture, wood-burning kitchen stoves and coal-fired power plants, these plumes of carbon dust rise over southern Africa, the Amazon basin and North America. But they are most pronounced in Asia, where so-called atmospheric brown clouds are dramatically reducing sunlight in many Chinese cities and leading to decreased crop yields in swaths of rural India, say a team of more than a dozen scientists who have been studying the problem since 2002.