Recent efforts by China to build more coal-fired power plants is reversing years of improvements in controlling pollution. And that's not all. Neighbouring countries, too, have to suffer the consequences.

The increase in power-plant construction has come in response to a persistent shortage of electricity. Most of China's power plants, old and new, are fuelled by coal and their smokestacks emit coal dust and sulphur dioxide into the air. Sulphur dioxide causes acid rain and also contributes to respiratory ailments. Air pollution has long been a problem in China, but it is taking a real turn for the worse.

Winds are carrying the noxious mix beyond China and over to next-door neighbours South Korea and Japan and even as far away as North America. This threatens to complicate the government's ties with key trading partners.