Why does Water Boil at less than 100°C at Higher Altitudes?
Water boils at a lower temperature on top of a mountain due to the decrease in atmospheric pressure as altitude increases. At sea level, the atmospheric pressure is about 101.3 kPa (kilopascals), and water boils at 100°C.
However, as altitude increases, the air pressure decreases. In higher altitudes, such as on top of a mountain, there are fewer air molecules exerting pressure on the surface of the water.
This lower pressure reduces the temperature at which water molecules can escape into the air as steam, thus causing the boiling point to drop. For example, at an altitude of around 2,000 meters (6,561 feet), water boils at approximately 93°C.
This phenomenon is important in cooking at high altitudes, as it can affect the time and methods needed to prepare food.