How does the atmospheric pressure affect us?
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1. Pressure increases the boiling point of liquids. If you have a glass of water, in a sense the water is always “trying” to boil away, even at room temperature; it just can’t because the weight of all the air above it is smooshing the water back into the glass. Removing air pressure reduces this barrier to liquids boiling. It’s an interesting tidbit that that means it takes noticeably less time to bring water to a boil at high elevation than at sea level – but more importantly, this pressure/boiling point thing also applies to your *blood.* This is why astronauts have to wear those big bulky suits – if exposed to the near-zero pressure of outer space, there would be nothing forcing their blood to remain a liquid, and it would start boiling inside them, and they would die.
2. For basically the same reason that pressure increases boiling point, pressure also increases how much gas (e.g. oxygen or carbon dioxide) a liquid is physically capable of dissolving. That’s important because e.g. if you go scuba diving in really deep water, the extra water pressure squeezing on you and your blood vessels makes your blood hold onto more and more oxygen with every breath. Which sounds good, but oxygen actually becomes poisonous at high enough pressures – and also if you dive really deep and dissolve a bunch of oxygen in your blood, and then surface really quickly, the sudden drop in pressure means your blood can’t keep all this extra oxygen dissolved, so it abruptly starts *bubbling* out of your blood, which is *lethally* bad. (See: [decompression sickness](https://en.wikipedia.org/wiki/Decompression_sickness)) Likewise at high elevation your blood is just simply not capable of holding onto as much oxygen as it is at sea level, which contributes to feeling light-headed and out of breath.
3. At higher air pressures, there is just simply *more air* to breathe in. At high elevation/low air pressure, there may not be enough oxygen available in the air to meet your body’s oxygen needs, even if your blood could hold onto all of it.
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