Before I talk about air pollution, you need to know all about our air. The Earth is surrounded by what seems like a huge ocean of air. Actually, a huge band of air stretches from the ground upward to about 500 miles – or 26,400 football fields! This band of air is called the atmosphere.

Air is a mixture. It contains many things – mostly gases we can’t see. Gases are neither solid nor liquid. They move around and do not have shape. The most important gas in air that people and animals use is oxygen. Oxygen has no color or smell.

On a breezy day, the air smells fresh and clean. Clean air is air that has no harmful levels of pollutants, like smog (ground-level ozone) or soot (fine particles). Clean air is good for people to breathe.

When too much soot and smog get into the air, the air is dirty or polluted. Polluted air is not good for people to breathe. So what exactly is smog and soot?