Dense fog blankets Cairo along the Nile River as the temperature drops, in Egypt, on Nov. 16, 2018. (Xinhua/Meng Tao)

Dense fog blankets Cairo along the Nile River as the temperature drops, in Egypt, on Nov. 16, 2018. (Xinhua/Meng Tao)

Dense fog blankets Cairo along the Nile River as the temperature drops, in Egypt, on Nov. 15, 2018. (Xinhua/Meng Tao)

Pigeons are seen flying in dense fog over Cairo as the temperature drops, Egypt, on Nov. 16, 2018. (Xinhua/Meng Tao)

Dense fog blankets Cairo along the Nile River as the temperature drops, in Egypt, on Nov. 16, 2018. (Xinhua/Meng Tao)