Air Pollution
Air Pollution is harmful stuff in the air that comes from cars, fires, and factories.
Think of it this way
A jar of clean air sits sealed on a counter. When you burn toast, tiny dark bits of smoke float up and spread through the jar. Those bits drift around and mix into the air inside. Now the air in the jar holds both clean air and dirty smoke bits.
Explaining air pollution by grade level
Cars and trucks burn fuel to move. That burning makes dirty smoke. The smoke goes up into the air we all breathe. Too much smoke makes the air bad for people and animals.