Condensation nuclei are tiny particles in the atmosphere that provide a surface for water vapor to condense upon, forming clouds. These particles can be dust, pollen, or even pollutants. Without condensation nuclei, water vapor would remain in the air as gas and not form liquid droplets, which are essential for cloud formation and precipitation. When water vapor cools and reaches its dew point, it condenses around these nuclei, creating droplets. This process is crucial for the water cycle, as it leads to the formation of clouds and eventually precipitation, impacting weather patterns and the environment.