Buildings are shrouded by fog in Shenyang, capital of northeast China's Liaoning Province, April 2, 2013. Local meteorological authorities issued an orange fog alert on Tuesday morning, and the visibility in the city was less than 500 meters. (Xinhua/Jiang Bing) 

Buildings are shrouded by fog in Shenyang, capital of northeast China's Liaoning Province, April 2, 2013. Local meteorological authorities issued an orange fog alert on Tuesday morning, and the visibility in the city was less than 500 meters. (Xinhua/Jiang Bing) 

Vehicles run in fog in Shenyang, capital of northeast China's Liaoning Province, April 2, 2013. Local meteorological authorities issued an orange fog alert on Tuesday morning, and the visibility in the city was less than 500 meters. (Xinhua/Jiang Bing)