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Comment by wyager | Hacker News Reader

A bunch of people here in CT have been posting pictures of weird white deposits on their cars from rain (which, apparently, is currently carrying stuff from OH). Seems like there's a pretty high chance that this ends up as one of those things where we may not be fully aware of the fallout (no pun intended) until years from now, if ever.

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This makes me think of the https://en.wikipedia.org/wiki/Seattle_windshield_pitting_epi...

Those “weird white deposits” are normal and have always been a thing. The rainwater evaporates but leaves some minerals behind

Yeah, isn't that normal precipitate?

I'd be worried about if there's ash from the burn off that then mixes with water to become lye. Not sure if there's more of a chemical reaction necessary than that.

I had a vinyl wrap on part of my car and some ash from California brushfires fell on it, and then it rained a month or so after (I was procrastinating on properly washing it off) and the lye produced ate through the clear coat of the vinyl.

There are minerals in rainwater? It's effectively distilled, no? How does it get minerals?

Rain is normally quite clean, but in certain circumstances can also pick up various other materials [1].

[1] https://en.wikipedia.org/wiki/Rain_dust

Maybe it picks up dirt particles from the air. In my experience, stuff that gets rained on can sometimes acquire dirt that it wouldn't otherwise have. If ky clothes are drenched from the rain, I throw them in the laundry instead of considering them clean.

Yes, but as with acid rain, rain can contain some non-waterthings, I think.

No doubt, but presumably those non water things are all things that evaporate, so wouldn't get left behind then the rain dries. The rain would have to pick up something up on the way down for it to contain something that precipitates out. That could be dust or soot, I'm not sure what else, but any minerals would have to come in that way

The water vapor will precipitate around airborne particles causing them to drop out of the sky.

The fact that I'm referring to them as "weird" means that they are not, in fact, normal. Presumably if any of these people had seen such a thing before, they wouldn't be so concerned about it.

Fair enough. I recently moved out of CT but talked to some people ik there after posting that and agree it is pretty unusual

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