In London, England, in 1952, the last days of November had been extra cold. People had shoveled more coal than ever into their fires. December 5 was a foggy, windless day. Lots of smoky fog covered London. It was as thick as pea soup. The thick smog hung over the city for several days. Thousands of people died from the Great London Smog.
Everyone needs clean, fresh air. The people of London learned about how air pollution can hurt them. They passed a law called the Clean Air Act. The law made sure people used less coal. Then, their city would have less smog. Smog is polluted air. They made sure that the stinky air went away from there! Europe still has a lot of air pollution. One study estimated that over 500,000 people die each year because of it.
Air is made up of gases and particles. Some of these gases are nitrogen, oxygen, and carbon dioxide. Air pollution happens when people add more gases and particles to the air. It comes from traffic. It comes from factories. This smoggy air causes many health problems.