Condensation is the reverse of evaporation and constitutes one of the fundamental mechanisms of the water cycle. It occurs when a humid air mass cools to its dew point, at which moment relative humidity reaches 100% and water vapour begins transforming into liquid droplets. This process releases latent heat, warming the surrounding air and potentially feeding convective processes. For condensation to occur in the atmosphere, condensation nuclei are required: microscopic particles of dust, sea salt, pollen, or pollutants upon which vapour deposits. Without these nuclei, air could reach extreme supersaturation without forming droplets. In clean air, the necessary supersaturation would be 300–400%, but with abundant condensation nuclei, just 0.1–1% suffices. The visible result of atmospheric condensation includes clouds, fog, and dew. The altitude at which condensation begins is called the condensation level and can be estimated from the difference between surface air temperature and dew point: for each degree of difference, the condensation level rises approximately 125 metres. This concept is key for predicting cloud bases and understanding thunderstorm formation.