What Is Acid Rain?

No, it’s not the unknown, never-released follow-up album to “Purple Rain” by the late, great Prince.

For a while in the 1970s and 80s, one could say that it was the only precipitation that fell from the sky in the industrialized world – at least, that was much of the belief in some circles during that time. There has been much progress in the last 40 years in regulating industry for the sake of the environment to reduce the amount of acid rain that falls from the sky in that it is less prevalent now that it has been.

But what is acid rain, exactly? To explain it, we’ll have to go back to your high-school chemistry class. Why? Because acid rain is, scientifically, not about any toxic rain, but precipitation that is impacted by certain specific gases. Anything else is just an impostor.

Acid rain is also not just rain; acid rain is the name given to any kind of precipitation that is impacted by either sulfur oxide (SO2) or any of the nitrogen-oxygen mixtures. There is such a thing as acid snow, sleet, hail, fog or dew. It all gets grouped under the “acid rain” terminology.

We do need to be clear, though. The air we all breathe does have some natural levels of these gases contained in it, so it doesn’t mean that any rain that falls in our everyday air is called acid rain. What constitutes acid rain is that precipitation that has a higher-than-normal concentration of sulfur oxide or a nitrous gas that causes the water in the atmosphere to have a lower pH than normal.  Normal pH for distilled water (with natural carbon dioxide left out) is 7.0, so any precipitation that has a pH lower than that is considered acidic.

What does acid rain do? What’s the big deal if it’s a little acidic?

Again, let’s go back to chemistry class. Do you remember creating an acid and seeing its effects? Acid has corrosive properties, and it can wear away all kinds of materials, from paper to wood to metal to rock. This can be especially the case with acid rain.

Over the years, acid rain (which was first reported on by scientists in the 1850s) has been known to make paint peel, kill insects and water life, adversely affect forests and freshwater sites, plus soil and even corrode steel, rock and brick on buildings.

The atmosphere does have these acidic gases naturally, but high concentrations mix with water cause damage. The high concentrations come from various sources, such as electricity generation, burning of fossil fuels, volcanic eruptions and heavy equipment or vehicles. Wind plays a large role in making acid rain a much larger concern than just in a region of the country where there are volcanoes or a lot of oil refineries.

Acid rain is still a thing, but it’s not as prevalent as it was 30 and 40 year ago before environmental regulations were put in place that restricted emissions from man-made sources.