Nitrogen and Oxygen make up 99% of the air.

A humidity level of 10% means there is not much water in the air.

ALL particulate matter in the air is caused by human activity

There are ______gases in the air we breathe.

The amount of water vapor in the air is called:

All of the following are mentioned as sources of water in the air except:

Particulate matter is tiny pieces of ______ that float in the air.

If your nose starts itching when you smell some flowers, it is probably caused by:

The most important message of this chapter is: People should__________

How do you say "carbón" in English?