BSIP, LECHENET / SCIENCE PHOTO LIBRARY BSIP, LECHENET / SCIENCE PHOTO LIBRARY
Air pollution. Smog hanging over a city, partially obscuring skyscrapers in the distance. Smog (smoky fog) occurs when atmospheric pollution builds up in city air, often reaching toxic levels. Smog is usually created by exhaust fumes from traffic and smoke from industries and power stations. In hot countries, a toxic 'photochemical' smog sometimes occurs when sunlight reacts with atmospheric pollutants. Photographed in Cairo, Egypt.
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