London Smog

One hundred years ago, the city of London was filthy dirty. People burned coal in private homes and factories. London's air filled with soot and was very unhealthy to breath. In 1925, the term smog was created by combining the words smoke and fog to describe the air pollution situation. London smog forms when particles of coal dust join with droplets of water in humid air. The cleanliness of London air has dramatically improved over the last century because of the decreasing popularity of burning coal.