A bridge is blanketed with advection fog in Datong, Shanxi province, Sept 2. Advection fog occurs when moist air is cooled by passing over a cool surface by advection (wind). It is most commonly seen at sea when moist air encounters cooler waters, including areas of cold water upwelling. A strong enough temperature difference over water or bare ground can also cause advection fog. [Photo/sxrb.com]

Woods are enveloped in advection fog in Datong, Sept 2. This natural phenomenon is commonly seen in coastal cities in North China but rare in the inland city Datong. [Photo/sxrb.com]