At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. read more
Because the atmospheric pressure is lower, the vapour pressure of the liquid needs to be lower to reach boiling point. Therefore, less heat is required to make the vapour pressure equal to the atmospheric pressure. The boiling point is lower at higher altitude. Here's a video that demonstrates the effect of atmospheric pressure on boiling point. read more
Normally, boiling water cannot cook food to more than 212 degrees Fahrenheit, as that is the boiling point of water under one atmosphere. By raising the pressure inside the vessel, however, a pressure cooker increases that temperature, allowing food to cook much faster. read more