Chapter 5, Problem 1RQ

To determine

The definition of condensation nuclei, and the reason why they are required toproduce clouds.

Answer to Problem 1RQ

Condensation nuclei serve as a surface for water vapor to condense in high altitude to cloud droplets.

Explanation of Solution

Cloud condensation nuclei are tiny, suspended particles upon which water vapor condensation takes place in the atmosphere.

Like dew and frost, it requires a surface such as grass or a car window to condense at or near the Earth's surface; condensation in high altitude also requires a surface such as airborne particles for the condensation of cloud droplets to occur.

Condensation nuclei are tiny bits of particulate matter such as microscopic dust, salt particles from ocean, smoke, and pollen grains that serve as a surface for the water vapor to condense high above the ground. Among these, ocean salt serves as good nuclei because they absorb water and are termed as “hygroscopic nuclei” (hygro=moisture, scopic=to seek).

These condensation nuclei are highly important because in their absence, a relative humidity excessing 100% is required to form clouds. However, this particulate matter that makes up the condensation nuclei is in abundance in the lower atmosphere. Hence, relative humidity rarely exceeds 101%.