Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)

Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)

Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)

Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)

Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)

Photo taken on Aug. 13, 2018 shows cloud and fog after a rainfall at Huangyaguan section of the Great Wall in the Jizhou District of Tianjin, north China. (Xinhua/Wang Guangshan)