From Kabul in Afghanistan to Hong Kong and Shijiazhuang in China, and from Lima to Sao Paulo in Latin America, people are increasingly suffering in severe toxic smogs - leaving hospitals and health clinics flooded with people with respiratory and heart problems.

Foul air has blanketed much of urban Asia for many weeks already in the northern winter. In Delhi, where there are nearly nine million vehicles, the high court has compared conditions to "living in a gas chamber"; Beijing and 10 other Chinese cities have issued red alert warnings; in Tehran, where mayor Mehdi Chamran says air pollution kills up to 180 people a day, the smog has been so bad that schools have been closed and sports banned.

According to the World Health Organisation, the toxic fumes of growing numbers of diesel-powered vehicles are combining with ammonia emissions from farming, wood and coal fires, tyre burning, open rubbish dumps, and dust from construction sites and brick kilns.