How does humidity work? Right now, where I live it is 73% humity and 75 degrees and it doesn’t feel humid. In Costa Rica, the numbers were similar and it felt like I was in a shower. I know it has to do with humidity, temps, and dewpoint. I just can’t wrap my brain around it.
In: Planetary Science
100% humidity is the maximum amount of water that the air can hold. Exactly how much water this is depends on temperature, so if you took a warm room at 50% humidity and cooled it down the humidity would rise – not because more water appeared but because the water that’s already there is getting closer to the maximum as the maximum is decreasing.
If you have a room at 100% humidity and cool it down, the extra water that can no longer be held gets dropped and becomes a liquid. When this happens outside, it forms dew. For any amount of water in the air, there’s a temperature where that would be 100% humidity and further cooling would cause liquid to form. This temperature is the dew point.
Humidity is a percentage or how much water is in the air, relative to how much it can handle. At 100% it is as moist as it can get. At 0% there’s no water at all.
The trick is, how much water fits in the air varies by temperature. The hotter it is, the more water (as measured by counting water molecules or whatever, in a given amount of space) you can have in the air. So at 70 degrees it might be 100% humid… but as the temperature rises, the humidity percent goes down since the warmer air can tolerate more water.
Which leads us to the opposite effect – when the air *cools*. The dew point is just the temperature when humidity reaches/might exceed 100%.. obviously that can’t happen, and it forces water out of the air. You see things like the grass and your car are wet even though it didn’t rain. From the previous example, the dew point would simply be 69-70 degrees.
On any day that isn’t *dry*, grab a cold beverage out of the fridge and just let it sit. The can/bottle/container gets wet all on its own. That’s dew, because the temperature of said beverage is lower than the dew point, and so water forms on it. It’s also why air conditioners often drip water.
Your body sweats as a means of cooling itself. Sweat evaporates, which naturally cools the body from the evaporation itself, but it can only evaporate if the air is dry enough to accept that sweat as more humidity. On a hot day, or if you’re out in the sun exercising with 100% humidity, sweating doesn’t work. With a humidity of 90% it works very slowly. If you’re in a situation of high humidity and you’re sweating, yeah, it’s a problem and you’re gonna get soaked, but more to the point it means you’re not cooling yourself properly – take precautions as heat stroke is a real threat.
Humidity measures the amount of water vapor in the air; how humid it feels also depends on temperature and dew point, which is the temperature at which the air becomes saturated with moisture, making higher temperatures feel more humid even with the same humidity percentage.
Lets take an example of a bathroom sponge which will represent the air in this example. If the sponge is completely dry, it can be said to have zero percent humidity. If you dip it in water, some of the water ‘evaporates’ into the sponge, raising it’s humidity. Eventually after repeated dippings the sponge is completely full, having 100% humidity.
Now, go ahead and squeeze that sponge. If the sponge is at 100% humidity any squeeze will release water back as liquid. However, if the sponge is only half full of water, squeezing it a little might not release any water. Further squeezing is required until it is dense enough for water to condense out.
Air works in a similar way as the sponge, where the dew point is the temperature ‘squeeze’ where the air can’t hold any liquid any more. As air cools it becomes more dense, thus squeezing the water out just like the bathroom sponge.
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