Here's why:

* What are condensation nuclei? Condensation nuclei are tiny particles in the atmosphere that act as surfaces for water vapor to condense upon. They can be things like dust, salt, smoke, or even pollen.

* How do clouds form? Clouds form when water vapor in the air cools and condenses into liquid water droplets. For this condensation to occur, the water vapor needs a surface to condense on. That's where condensation nuclei come in.

Without condensation nuclei, clouds would be much harder to form. The water vapor would need to cool to an extremely low temperature before it could condense on its own.