Rain's Dirty Little Secret

Raindrops form when water vapor condenses onto microscopic dirt particles in the atmosphere. Water molecules naturally bond but need cooling past the dew point to form stable clusters. However, clusters must reach a critical size of 150 million molecules to grow, which is unlikely without dirt particles. These particles act as catalysts, allowing clusters to start at the critical size, leading to raindrop formation. This process is essential for life on Earth.

Why are microscopic dirt particles essential for raindrop formation?

• They provide a surface for water vapor to condense.

• They increase the temperature of the air.

• They absorb water vapor from the air.

• They prevent water molecules from sticking together.

What happens to water vapor molecules when the air temperature reaches the dew point?

• They stop moving entirely.

• They evaporate more quickly.

• They condense into larger clusters.

• They disperse into the atmosphere.

What is the critical size a water cluster must reach to grow into a droplet?

• 10 molecules

• 5 molecules

• 50 molecules

• 150 million molecules

How do dirt particles assist in the formation of raindrops?

• They repel water molecules.

• They heat the surrounding air.

• They dissolve in water.

• They provide a starting point for water clusters.

What is the likelihood of a small water cluster growing into a droplet without dirt particles?

• Low

• Very high

• Impossible

• Moderate