Corrosive Precipitation: A Review on Acid Rain

If you have played Roblox before, you may have encountered “acid rain” in one of the rounds of your Natural Disasters game mode. In this game, your objective is to remain indoors with a roof above your head in order to stay away from the hazardous rain that falls from the sky. When the rain comes in contact with your avatar, it immediately causes damage to your health bar. From this game, some movies, and the name “acid rain” itself, you may believe that during acid rain, actual toxins and dangerous chemicals rain down from the sky. You might believe that the rain is deadly pure acid that melts straight through anything it comes in contact with. However, these demonstrations of acid rain couldn’t be further from the truth.

So what is acid rain? The acidity of acid rain actually refers to its pH. Acid rain is any form of precipitation that has been mixed with elements to cause it to become more acidic. While pure water rainfall has a neutral pH of 7.00, acid rain consists of precipitation with a pH of around 6.00 or less, generally between 4.20 and 4.40. The substances that make acid rain this acidic are the high levels of nitric and sulfuric acids contained in the precipitation.

What is pH? pH is a term used in chemistry to quantitatively measure the acidity or basicity of a substance. More specifically, it refers to the measurement of the concentrations of hydrogen ions (H+) and hydroxide ions (OH-) within a substance. pH is measured on a scale from 0.00 to 14.00. When a substance is referred to as acidic, its pH is closer to 0.00. Acidic substances contain higher concentrations of hydrogen ions and low concentrations of hydroxide ions. When a substance is referred to as basic, its pH is closer to 14.00. Basic substances contain lower concentrations of hydrogen ions but higher concentrations of hydroxide ions. When a substance has a pH of 7.00, it is considered neutral, neither acidic nor basic. A substance that is considered neutral is pure water.

Source: Environment Protection Agency

Why is this dangerous? While direct contact with acidic precipitation might not cause immediate harm, its long-term effects on the environment could be detrimental. All living organisms maintain homeostasis—a state of equilibrium in physical and chemical conditions that is essential for proper functioning. This means that organisms must adapt to environmental changes, such as shifts in pH levels, temperature, and water content. However, there are limits to this adaptability. Organisms can only survive within specific ranges of environmental factors, including pH and temperature. If an organism is exposed to conditions outside its optimal range, its internal processes can fail, leading to death. 

This is particularly relevant to pH levels. When an organism is placed in an environment where the pH is outside its tolerable range, the proteins in its cells may denature and cease to function, causing the organism's systems to shut down. 

In the context of acid rain: Acid rain significantly impacts aquatic environments like lakes and streams by increasing their acidity. This disrupts the aquatic ecosystem because the organisms within it cannot function properly in more acidic conditions. Moreover, acid rain releases gaseous acids into the atmosphere, further contributing to environmental stress. These air pollutants may also contribute to global warming, the main cause of climate change.

As a disclaimer though, the environment can naturally adapt to certain amounts of acid rain because of the basicity of some elements within the environment. For example, soil is often slightly basic because of the naturally occurring limestone within it, making it able to counteract the acids, neutralizing the acidity of the precipitation. However, most other environments with no limestone are affected by acid rain.

Acid rain can also affect structural monuments and statues. Because most of these structures are made from limestone, sandstone, marble, or granite, they are susceptible to corrosions when they come in contact with acid rain. To exemplify, when airborne sulfur dioxide mixes with water, it produces sulfuric acid (H2SO3). When the sulfuric acid precipitation comes in contact with one of the materials, for example limestone, which is made out of calcium carbonate (CaCO3), these chemical compounds react with one another through a double replacement reaction, producing calcium sulfate (CaSO4). Calcium sulfate is soluble, which causes the structures to slowly crumble and erosion.

Ultimately, acid rain is a human-induced environmental disaster. While it may not appear as dramatic as portrayed in games and movies, its long-term impact on the environment is significant. As a society, we must remain aware of the consequences of our actions and work to mitigate the lasting effects on our planet. I hope you learned something new! Keep a lookout for the next post!

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References

Let’s Talk Science. (2019 Aug. 21). What is Acid Rain?. Let’s Talk Science. Retrieved February 27, 2023, from https://letstalkscience.ca/educational-resources/stem-in-context/what-acid-rain

Nunez, C. (2019 Feb. 28). Acid rain, explained. National Geographic. Retrieved February 27, 2023, from https://www.nationalgeographic.com/environment/article/acid-rain

Water Science School. (2019 Aug. 2). Acid Rain and Water. USGS. Retrieved February 27, 2023, from https://www.usgs.gov/special-topics/water-science-school/science/acid-rain-and-water’