Citizens do morning exercises amid heavy fog in Hongze County, east China's Jiangsu Province, Jan. 14, 2013. Emergency response measures were adopted in many Chinese cities, where the air has held excessive levels of major pollutants in the past few days due to prolonged fog and smog. Heavy fog has caused highway closures and flight delays in several provinces. The elderly, children and those suffering from respiratory and cardiovascular diseases are advised to stay indoors to reduce exposure to polluted air. [Xinhua]