Residents walk through a street in Shenyang, capital of northeast China's Liaoning Province, on Oct. 31. Local meteorological station issued an orange alert-the second highest warning-for dense smog early Friday morning, as the air quality indexes hit the maximum of 500 from many monitoring stations in the city. According to the Ministry of Environmental Protection, air pollution is "serious" when AQI is between 301 and 500. [Photo/Xinhua]