The 100 m false-colour image of 13 January 2015 shows us a view of the Zhongtiao Mountains, a major mountain range located in the south of China’s Shanxi Province, covered with smog. Smog is unhealthy to humans and animals. Smog is common in big cities with a lot of industry and traffic. Cities located in basins surrounded by mountains may have smog problems because the smog is trapped in the valley and cannot be carried away by wind.