I remember the first time I ever saw that white vapor coming down from the vents above me – you know the one I’m talking about, right? – I had no idea of what it was and it scared the crap out of me – I figured the plane was on fire and why wasn’t anyone doing anything about it?
(Note: yes, I know the video is upside down. My phone is doing weird stuff and capturing photos and video backwards. I uploaded it to YouTube without editing it because I thought YT had a video editor onboard. But it turns out they ended that about a year ago. Go figure. But really…it’s 6 seconds and it’s vapor. You get the gist, even if it is upside down. It’s just not worth pulling out the iMovie software for…)
Have you ever wondered what it is? Why it is? I did. So I went and found out…
It turns out it all has to do with water vapor and dew points and condensation and other stuff that I memorized in high school for a Science class and then promptly forgot when the test was over.
Essentially, the cabin was filled with warm, moist (humid) air from the outside (because the cabin door was open, because people were loading onto the plane) and the dew point (science class: the atmospheric temperature [varying according to pressure and humidity] below which water droplets begin to condense and dew can form) was close to the air temperature inside the plane. However the air conditioner was on, so the temperature around the AC vents lowered the dew point, which caused the invisible water vapor (gas) condensation to turn into visible water droplets (liquid) – that’s the vapor/fog/etc. you’re seeing.
As the water droplets are blown further away from the AC vents, the air is once again warmer and the water vapor turns into a(n invisible) gas again. That’s why you usually only see the smoke/mist near the AC vents and not throughout the cabin (although that can happen too, if the cabin is that hot and humid and the AC is that cold).
Because the cabin air will be recirculated throughout the flight and the water separators in the AC system will take out most of the moisture from the air with time, you generally only see this phenomenon at the beginning of the flight, when the cabin door is open.
Oh, this generally only happens in the summertime, when the air outside is warm and (wait for it) moist (sorry not sorry, for those of you who don’t like that word).
Here’s a better video that I found on YouTube, and this one is even right-side up.
So yeah, that’s my (been a really long time since I took a science class) understanding of it. You can also click here, if you’d like, for what might be a better explanation.
And now you know 🙂
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This post first appeared on Your Mileage May Vary