What's air pollution and why's it so important?

Air pollution is a term you've probably come across before.

It describes the harmful gases and particles in the air. We can't always see these substances as many are invisible to the human eye, but they affect the quality of the air around us and this can be very damaging to both human health and the environment.

Air pollution affects us all, but why is so important?

We spoke to Andrea Lee from the charity ClientEarth to find out more.