The cold weather currently affecting Taiwan is due to a cold air mass moving down from China. It is also due in part to pollutants carried over from China.
The Taiwan News today reports,
The Environmental Protection Administration yesterday cautioned the public to stay indoors for the following days as pollutants from China are expected to affect Taiwan's air quality starting tomorrow.
EPA official Chang Shun-chin (張順欽) said that based on the EPA report, the cold current that has loomed over Taiwan since last Friday is actually a mass of "dirty wind." The maximum aerosol density detected on Sunday in Wanli, Taipei County was three times higher than normal, Chang said.
He explained that the poor air quality people have been experiencing in recent days was not produced by sand storms. Instead, he said, it was caused by the pollutants produced along the coastal area in China.
The large concentration of aerosols in the atmosphere can actually cause local cooling. An article from National Geographic says,
"While many parts of Earth are warming up because of greenhouse gases, in places where there are huge concentrations of aerosols, there is actually cooling," said Huebert. In April, for example, the surface cooling effect of aerosols downwind of Asia is 10 percent higher than warming caused by greenhouse gases, Huebert notes.
The Asian brown cloud is a phenomena that can be observed over much of the Asian continent, particularly India and China. It has significant effects on regional weather patterns. More information about the cloud with graphics can be found on this page by NASA and in this detailed report by the UNEP.