smog

Imagine a city hidden behind a thick, gray haze. That is often what smog looks like. It is a kind of dirty air pollution, usually caused by cars, factories, and other human activity. It is not just ugly to look at; it can also be harmful to breathe. Think of Los Angeles in the 1970s, a city strongly linked with this kind of pollution. While things have improved in some places, it still affects many big cities around the world. You might hear about "smog alerts" that warn people to stay indoors when pollution levels are very high.

Smog is a type of air pollution that reduces visibility and can harm human health. The word itself is a portmanteau, a blend of "smoke" and "fog." But the real meaning is more complex than just those two things.

Historically, smog was often caused by industrial emissions containing sulfur dioxide and tiny particles, especially in colder climates where fog was common. A well-known example is London's "pea-soupers" in the 1950s. This is often called classical smog.

Today, however, most smog, especially in cities like Los Angeles, Beijing, or Delhi, is photochemical smog. This type forms when sunlight reacts with pollutants released by vehicles and industrial facilities, creating a hazy mixture of ozone, nitrogen oxides, and other harmful chemicals.

Smog is not just an appearance problem; it can cause breathing problems, heart problems, and may also contribute to climate change. Scientists study its composition to understand where it comes from and how to reduce air pollution. You might read about "smog reduction targets" in environmental policy discussions or see images of cities covered by thick haze during peak pollution seasons. So, while the word sounds simple, it refers to a serious environmental problem with real health effects.