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How does water vapour condense to form clouds?

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Diagram illustrating Earth's environmental spheres, with labeled sections showing the geosphere (land and crust), biosphere (living things), atmosphere (air), and hydrosphere (water), each extending vertically from the Earth's surface. — hydrosphere Earth's environment includes the atmosphere, the hydrosphere, the lithosphere, and the biosphere.

Clouds form when moist air rises and cools, a process primarily driven by the vertical movement of air. As an air mass ascends, it encounters lower atmospheric pressure, causing it to expand and cool adiabatically—meaning it cools without exchanging heat with the surrounding environment.12

As the air cools, its capacity to hold water vapour decreases. When the temperature drops below the dew point, the air becomes supersaturated, and the water vapour begins to condense. This condensation occurs on tiny suspended particles known as condensation nuclei, such as dust, sea salt, or combustion particles. These nuclei act as essential sites that allow water molecules to gather and transition from a gaseous state into liquid water droplets or, in colder temperatures, deposit as ice crystals.1234

When these droplets or crystals exist in large quantities, they become visible as a cloud. While condensation is the fundamental mechanism for cloud formation, the process is sustained by upward-moving air currents that keep these particles suspended in the atmosphere.12