London had always been known for its fog on chilly days. Although the fog sometimes made the city appear gloomy, it was harmless. Fog is nothing but microscopic drops of water trapped in the air.
By the 1800s, however, London had become more crowded and modern. Pollution from factories and chimneys, much of it caused by burning coal, filled the air. On cold and foggy days, dirty smoke would stick to the tiny drops of water in the air. In 1905, this dark, dirty air got a name: smog.
Smog wasn’t a problem only in London. The early 1900s was a time of growth all over Europe—and the United States. Smoke from factories and steel mills turned cities ugly.
Most people thought nothing could be done to make the air cleaner. Coal was the cheapest way to heat a home, and it was the only affordable option for most people.
And if factory owners closed their factories, millions of people would end up unemployed.
Smog, it seemed, was simply a fact of city life.