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Boiling point refers to a specific temperature when a liquid changes phase from liquid to gas. At that point, the molecules of liquid have enough energy to overcome the vapor pressure pushing down upon the liquid and become gas molecules. At or around sea level, the boiling point of water, for example, is 212 degrees F or 100 degrees C. However, that temperature is not absolute -- if you have a sealed flask of water, and reduce the pressure in the flask (which is the same thing as lowering the vapor pressure) and heat the water, it will boil at a lower temperature. Conversely, if you add pressure to the flask, the amount of energy the liquid molecules need to overcome the vapor pressure increases, so the temperature at which the liquid boils increases.
The barometric pressure changes from day to day (and hour to hour in some places) and so changes the boiling point, increasing when the pressure increases, decreasing when the pressure decreases. See a pressure / temperature calculator at the link:
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