Where I live now there can be significantly acidic rain. The government posts measurements for many cities and there can be stretches for days or longer with reported pH of 3.2 or 3.1. I even saw 2.9 reported once.

While this can have quite serious environmental effects depending on a number of factors including total rainfall, geology, geography, soil composition just to name a few, my question is about the direct effect of rainfall this acidic on people and their possessions.

Just how dangerous or deleterious to people and their immediate possessions (e.g. clothing, other objects) would getting a bit of pH 3.1 rain on oneself actually be? Would it sting at all if it got in the eye? Discolor hair? Is there any basis at all to being collectively phobic of being touched by this rain specifically because of its pH?

I've tried searching the internet but there is a jumble of information there. As far as I can tell, pH 3.1 seems to be somewhere between a soft drink, and tomato juice, but this is from unreliable sources.

So I thought I would ask in Chemistry SE for a solid, scientific answer. I'm not looking for an opinion, or a reasoned answer (e.g. "if it was that dangerous, then..."). I'd prefer factual data, or references related to safety and effects of topical exposure to (mildly) acidic water.

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    $\begingroup$ Well I guess rain falls on you from time to time and it seems you didn't notice anything... And comparisons with juice or drink are OK $\endgroup$ – Mithoron Apr 10 '16 at 18:58
  • $\begingroup$ If you google "pH of common substances site:.gov" (no quotes), you'll get several reliable(ish) links that confirm your understanding that 3.1 is about as acidic as a soft drink, and much less acidic than lemon juice. 3.1 seems really acidic because it's closer to pH 0 than to pH 7, but pH is a logarithmic measurement, so it's really not as bad as it seems. $\endgroup$ – user28114 Oct 23 '16 at 18:57
  • $\begingroup$ @barrycarter I have heard of logarithmic scales before, thanks. pH of 3.1 means there is almost one H${}^+$ (or H${}_3$O${}^+$) ion for every thousand water molecules, and I think that's a lot. But my question here is rather specific - I'm asking about the chemical effect of said pH on people or personal belongings, not if it sounds big to them or not. $\endgroup$ – uhoh Oct 23 '16 at 22:57

According to a United States Environmental Protection Agency report on the effects of acid rain on human health:

Walking in acid rain, or even swimming in a lake affected by acid rain, is no more dangerous to humans than walking in normal rain or swimming in non-acidic lakes. However, when the pollutants that cause acid rain $\ce{—SO2}$ and $\ce{NOx}$, as well assulfate and nitrate particles— are in the air, they can be harmful to humans.

$\ce{SO2}$ and $\ce{NOx}$ react in the atmosphere to form fine sulfate and nitrate particles that people can inhale into their lungs. Many scientific studies have shown a relationship between these particles and effects on heart and lung function, such as asthma and bronchitis.

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  • $\begingroup$ Thank you for the attention to my question and the EPA link! I noticed that the EPA page What is acid rain? puts the pH of acid rain in the general area of 4.3 plus "Acid rain usually has a pH between 4.2 and 4.4." - I've seen values as low 2.9 reported by the national weather service here, and 3.1 much more often, thus the title of the question. I hadn't known about the serious risks associated with breathing sulfate and nitrate particles (as opposed to gas) and I'll read further about that. Thanks! $\endgroup$ – uhoh Mar 4 '17 at 4:46
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    $\begingroup$ No problem. As an aside, I did come across a story about acid rain after volcanic events that had rain with pH ~2 that would irritate people's eyes. But that's some really acid rain! $\endgroup$ – airhuff Mar 4 '17 at 4:53

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